{"gene":"SCG5","run_date":"2026-06-10T07:46:29","timeline":{"discoveries":[{"year":1994,"finding":"7B2 (SCG5) acts as a neuroendocrine chaperone that specifically associates with the precursor form of prohormone convertase PC2 (proPC2) in the early secretory pathway; the interaction is transient, commencing in the ER and dissociating in later compartments coincident with cleavages of 7B2, proPC2, and prohormone. The amino-terminal half of 7B2 is distantly related to chaperonins.","method":"In vitro incubation with recombinant 7B2 and newly synthesized pituitary proteins; metabolic cell labeling and co-immunoprecipitation; pulse-chase analysis in Xenopus intermediate lobe cells","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal co-IP, pulse-chase, in vitro binding assay; independently confirmed by multiple subsequent studies","pmids":["7913882"],"is_preprint":false},{"year":1994,"finding":"Intact recombinant 7B2 is a potent, specific inhibitor of PC2 enzymatic activity in vitro but does not inhibit the related convertase PC1/PC3. The 7B2 cleavage product (C-terminal half removed) is virtually inactive as an inhibitor. The carboxyl-terminal half of 7B2 is distantly related to the potato inhibitor I family of subtilisin inhibitors.","method":"In vitro enzyme inhibition assays using recombinant 7B2 against PC2 and PC1/PC3; sequence homology analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution assay with recombinant proteins; replicated in multiple subsequent studies","pmids":["8016065"],"is_preprint":false},{"year":1995,"finding":"Overexpression of 21-kDa 7B2 (the naturally occurring maturation product of 27-kDa pro-7B2) greatly facilitates the kinetics of proPC2 maturation and is required for the generation of enzymatic activity; the N-terminal 'chaperone' domain alone was insufficient. PC2 enzymatic activity was inhibited by the 7B2 carboxyl-terminal peptide, confirming specificity.","method":"Stable transfection of neuroendocrine cell lines (AtT-20/PC2, Rin5f, CHO/PC2) with 7B2 constructs; pulse-chase metabolic labeling; fluorogenic substrate enzyme activity assay; inhibition by 7B2 CT peptide","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro activity assay, multiple cell lines, domain mutagenesis; replicated by other labs","pmids":["7790360"],"is_preprint":false},{"year":1995,"finding":"Within the ER, pro-7B2 specifically binds proPC2 but not other convertases (furin, PC1, PACE4, PC5). This binding is Ca2+-dependent and does not require N-glycosylation of proPC2. Mutagenesis of the pentabasic RRKRRS site in pro-7B2 (critical residues R152, R151, S156) abolished or greatly diminished binding. After furin cleavage in the TGN, 7B2 remains bound to PC2, suggesting a second Ca2+-dependent binding site.","method":"Biosynthetic pulse-chase analysis; co-immunoprecipitation; site-directed mutagenesis of pro-7B2; calcium chelation experiments in neuroendocrine cells","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP with mutagenesis, multiple orthogonal methods, replicated across labs","pmids":["7722516"],"is_preprint":false},{"year":1995,"finding":"The carboxyl-terminal portion of 7B2 (CT peptide, residues ~155–185) is responsible for PC2 inhibition. A short segment containing a Lys171-Lys172 dibasic site is critical; single and double mutations at this site strongly diminished or abolished inhibitory potency. No 7B2 mutant inhibited PC1/PC3.","method":"In vitro mutagenesis; prokaryotic expression of mutant 7B2 proteins; in vitro enzyme activity assays against PC1/PC3 and PC2","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis, multiple truncation and point mutants tested","pmids":["7782286"],"is_preprint":false},{"year":1995,"finding":"Immunopurified PC2 cleaves the fluorogenic substrate Cbz-Arg-Ser-Lys-Arg-AMC in a Ca2+-dependent manner (half-maximal stimulation at 75 µM Ca2+, pH optimum 5.0). The 27-kDa 7B2 is a tight-binding inhibitor of PC2 with Kd = 7.3 nM. The 7B2 CT peptide (residues ~155–185) is a potent inhibitor (Ki = 57 nM) and can block PC2-mediated proenkephalin processing; 21-kDa 7B2 is functionally inactive as a proteinase inhibitor.","method":"Immunopurification of PC2 from mouse insulinoma cell conditioned medium; fluorogenic substrate assay; inhibitor kinetics with recombinant 27-kDa 7B2 and synthetic CT peptides; in vitro cleavage of recombinant proenkephalin","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic characterization with purified components, Ki and Kd quantification","pmids":["7727407"],"is_preprint":false},{"year":1996,"finding":"Active recombinant PC2 was purified to homogeneity from conditioned medium of CHO cells co-expressing PC2 and 21-kDa 7B2. 21-kDa 7B2 copurifies with activated PC2 and provides significant stabilization against thermal denaturation in a Ca2+- and pH-dependent manner (optimal at millimolar Ca2+, pH 5–6), consistent with a role for 7B2 in stabilizing PC2 activity within secretory granules.","method":"Purification of recombinant PC2; thermal denaturation assays; enzyme activity assays; gel filtration to remove associated 7B2 followed by re-addition","journal":"Archives of biochemistry and biophysics","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified components, multiple orthogonal activity and stability assays","pmids":["8660652"],"is_preprint":false},{"year":1994,"finding":"Pro-7B2 is tyrosine-sulfated in the trans-Golgi network and cleaved by a furin-like convertase at the RXKR/RRKRR site within the TGN to generate the 23-kDa form; PC1 and PC2 cannot process pro-7B2. Protein transport to Golgi compartments is required for this processing (blocked by monensin, brefeldin A, or low temperature).","method":"Recombinant vaccinia virus expression in multiple cell lines (AtT-20, PC12, GH4C1, Ltk-); mutagenesis of P4 Arg; co-expression with PC1, PC2, furin; expression in furin-deficient LoVo cells; [35S]SO4 pulse-chase; monensin/brefeldin A treatments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple cell lines, furin-deficient cells, site-directed mutagenesis, pharmacological inhibitors","pmids":["8034690"],"is_preprint":false},{"year":1996,"finding":"PC2 itself cleaves the 7B2 CT peptide at an internal Lys-Lys site in secretory granules; the resulting cleavage product is non-inhibitory after removal of terminal lysines by carboxypeptidase E (CPE). This provides a mechanism for intracellular inactivation of the CT peptide inhibitor.","method":"Metabolic labeling ([3H]valine) and immunoprecipitation in multiple cell lines; RIA against CT peptide carboxyl terminus; in vitro incubation of 125I-CT peptide with purified recombinant PC2; synthetic CT peptide derivative inhibitory assays; inclusion of CPE in reactions","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified PC2, multiple cell lines, corroborated by RIA and activity assays","pmids":["8643504"],"is_preprint":false},{"year":1997,"finding":"7B2 does not promote early proPC2 folding; instead, proPC2 must fold before it can bind 7B2. Once bound, 7B2 facilitates proPC2 transport from the ER to the Golgi and is required for proPC2 activation at acidic pH. ProPC2 activation could be reconstituted in Golgi-enriched subcellular fractions in vitro and required 7B2.","method":"Pulse-chase labeling; N-glycanase F sensitivity assay; inhibition of proPC2 folding experiments; co-immunoprecipitation; subcellular fractionation; in vitro proPC2 activation assay in Golgi-enriched fractions","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — subcellular fractionation, in vitro reconstitution in Golgi fractions, multiple orthogonal methods","pmids":["9348280"],"is_preprint":false},{"year":1996,"finding":"A polyproline helix-like (PPII) structure within the N-terminal domain of 7B2 (around Pro90, Pro91, Pro93, Pro95) is required for interaction with proPC2. Point mutagenesis of critical prolines severely impaired or abolished 7B2 bioactivity as measured by four assays: co-immunoprecipitation with proPC2, facilitation of proPC2 maturation, acquisition of PC2 enzymatic activity, and thermal protection of PC2. An adjacent predicted alpha-helix (residues 107–123) also contributes.","method":"Site-directed point mutagenesis; co-immunoprecipitation; proPC2 maturation assay; PC2 enzymatic activity assay; thermal protection assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis with four independent functional assays in the same study","pmids":["8798569"],"is_preprint":false},{"year":1998,"finding":"The PC2 proregion is required but not sufficient for 7B2 binding; the P domain stabilizes PC2 structure and is not interchangeable with PC1's P domain; the C-terminal domain is not involved in 7B2 binding. A single residue in the PC2 catalytic domain, Tyr-194, is required for 7B2 binding and proPC2 activation; Y194 is located within a surface-exposed loop rich in aromatic amino acids.","method":"Sequential domain deletions, site-directed mutagenesis, and PC2/PC1 domain-swapping chimeras expressed in AtT-20 cells; co-immunoprecipitation; maturation assay; enzymatic activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — systematic domain swapping and point mutagenesis with multiple functional readouts","pmids":["9422782"],"is_preprint":false},{"year":1998,"finding":"7B2 is essential for proteolytic conversion and activation of proPC2 in vivo: cells expressing PC2 but not 7B2 (SK-N-MCIXC neuroepithelioma) contain only inactive proPC2 forms; stable transfection with pro-7B2 rescued secretion of mature, active 68-kDa PC2. In a model of hypoglycemic shock, decreased adrenomedullary 7B2 expression correlated with increased proPC2:PC2 ratio.","method":"Immunoblotting of cell fractions; stable transfection of 7B2 cDNA into PC2-expressing cells; insulin-induced hypoglycemic shock animal model; comparison of developing rat brain PC2 forms","journal":"DNA and cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple in vivo and cell-based models converging on same conclusion; replicated finding","pmids":["9881669"],"is_preprint":false},{"year":1999,"finding":"7B2 null mice have no demonstrable PC2 activity, are deficient in processing islet hormones (hyperproinsulinemia, hypoglucagonemia), and develop lethal Cushing's syndrome from pituitary intermediate lobe ACTH hypersecretion. This establishes that 7B2 is absolutely required for PC2 activation in vivo and has additional functions in regulating pituitary hormone secretion beyond PC2.","method":"7B2 null mouse (knockout via transposon-facilitated technique); comparison with PC2 null phenotype; measurement of circulating hormones (ACTH, corticosterone, insulin, glucagon); histology","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with specific phenotypic readouts, comparison to PC2 null, replicated","pmids":["10089884"],"is_preprint":false},{"year":1999,"finding":"A minimal 36-residue internal peptide of 7B2 (containing the proline-rich sequence, an alpha-helix, and the only disulfide bond) contains all information required for proPC2 activation. Mutation of the alpha-helix or the cysteines forming the disulfide bond abolished proPC2 activation activity.","method":"Sequential deletions of 7B2; mutagenesis of alpha-helix and cysteine residues; four functional assays: proPC2 binding, maturation facilitation, in vivo and in vitro proPC2 activation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic deletion mapping and mutagenesis with multiple orthogonal assays","pmids":["10409712"],"is_preprint":false},{"year":1996,"finding":"Dissociation of the N-terminal 7B2 fragment from proPC2 precedes (and is not directly linked to) proPC2 maturation; proPC2 maturation does not occur while associated with intact 7B2 precursor. The C-terminal region of 7B2 is necessary and sufficient for inhibition of proPC2 conversion in vitro.","method":"Pulse-chase analysis in Xenopus and mouse intermediate pituitary cells; in vitro conversion assay with recombinant 7B2 and truncation mutants","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — cell-based pulse-chase and in vitro reconstitution with deletion mutants","pmids":["8681965"],"is_preprint":false},{"year":2000,"finding":"Residues 242–248 in the PC2 catalytic domain (PC2-specific sequence) are required for binding to 21-kDa 7B2 and for inhibition by the 7B2 CT peptide; replacement with corresponding PC1 residues greatly reduced 7B2 binding and nearly abolished CT peptide inhibition, without profoundly altering substrate cleavage specificity.","method":"Site-directed mutagenesis of PC2 catalytic domain; co-immunoprecipitation with 7B2; in vivo proenkephalin and POMC cleavage assays; in vitro fluorogenic substrate assay; CT peptide inhibition assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis with multiple functional readouts","pmids":["10799554"],"is_preprint":false},{"year":2000,"finding":"Drosophila 7B2 (d7B2) and rat 7B2 can both support dPC2 (amontillado) secretion and activity in Drosophila S2 insect cells but not in HEK-293 cells, demonstrating that dPC2 requires insect cell-specific posttranslational processing events for maturation and secretion, and that 7B2–PC2 interaction is evolutionarily conserved.","method":"Transfection of dPC2 and d7B2/r7B2 cDNAs into HEK-293 and S2 cells; PC2 activity assays; immunoblotting; pulse-chase labeling","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two cell systems compared, enzymatic activity and immunoblot, single study","pmids":["10749852"],"is_preprint":false},{"year":2001,"finding":"Cleavage at the 7B2 furin consensus pentabasic site is required for production of PC2 capable of efficiently cleaving the inhibitory CT peptide. When the furin site is blocked (blockade mutant), intact 27-kDa 7B2 accumulates and PC2 secreted with it lacks ability to inactivate the CT peptide, although proPC2 activation per se does not require furin cleavage when the CT peptide is non-inhibitory.","method":"Construction of 7B2 mutants (CT peptide KK→SS; furin site blockade; double mutant); cell-free proPC2 activation assay; transient transfection into HEK293 cells; measurement of PC2 activity and CT peptide forms in conditioned medium","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — cell-free reconstitution plus cell-based transfection, multiple mutants, single rigorous study","pmids":["11677272"],"is_preprint":false},{"year":2002,"finding":"Mortality in 7B2 null mice is caused by elevated corticosterone secondary to ACTH hypersecretion; adrenalectomy rescues survival and normalizes pituitary dopamine (which is reduced to ~25% of WT in 7B2 nulls), circulating ACTH, and corticosterone. This indicates a 7B2-mediated dopaminergic deficiency contributes to ACTH hypersecretion.","method":"Adrenalectomy of 7B2 null mice; measurement of circulating ACTH, corticosterone, pituitary dopamine; comparison with PC2 null mice","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic null rescue experiment with hormonal and neurochemical readouts","pmids":["11854475"],"is_preprint":false},{"year":2005,"finding":"7B2 can be phosphorylated at Ser115 (and additional serine/threonine residues) by Golgi kinases in Rin cells and chromaffin cells but not AtT-20 cells. Phosphorylated 7B2 is unable to bind proPC2 (co-immunoprecipitation) and is impaired in facilitating proPC2 activation (cell-free assay), functionally inactivating it in a manner analogous to BiP phosphorylation.","method":"Metabolic 32P labeling; phosphoamino acid analysis; site-directed mutagenesis of Ser115; co-immunoprecipitation of phospho-7B2 with proPC2; cell-free proPC2 activation assay; in vitro Golgi kinase phosphorylation with kinase inhibitors","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis confirming phosphorylation site, two independent functional assays, in vitro kinase identification","pmids":["16286464"],"is_preprint":false},{"year":2008,"finding":"7B2 possesses chaperone activity that prevents unfolding and aggregation of proPC2; addition of exogenous recombinant 7B2 to CHO cells expressing proPC2 prevented secreted PC2 aggregation in a dose-dependent manner. Intracellular proPC2 exists in part as higher-order oligomers, reduced by co-expressed 7B2. Velocity sedimentation showed 7B2 solubilizes three PC2 species from precipitable aggregates. An activation-competent PC2 conformation cannot be maintained without 7B2.","method":"Aggregation assays; enzymatic activity assays; chemical cross-linking; sucrose density gradients; velocity sedimentation; addition of exogenous recombinant 7B2 to cells","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal biophysical and biochemical methods in single study","pmids":["18467442"],"is_preprint":false},{"year":2012,"finding":"7B2 suppresses fibrillation and aggregation of Aβ(1-42), Aβ(1-40), and α-synuclein in vitro at 1:10 molar ratio. In Neuro-2A cell culture, extracellular or adenovirally overexpressed 7B2 blocked neurocytotoxicity of Aβ(1-42) and increased cell viability; RNAi knockdown of 7B2 increased Aβ(1-42)-induced cytotoxicity. In APP/PSEN1 mouse brains and human AD/PD brains, 7B2 co-localizes with Aβ plaques and α-synuclein deposits.","method":"In vitro fibrillation/aggregation assays (ThT fluorescence); adenoviral overexpression; RNAi knockdown; cell viability assays; immunofluorescence co-localization in mouse model and human postmortem brain","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro reconstitution with gain- and loss-of-function cell studies plus in vivo co-localization","pmids":["23172224"],"is_preprint":false},{"year":2013,"finding":"21-kDa 7B2 blocks hIAPP (islet amyloid polypeptide) fibrillation in vitro and protects Rin5f cells from hIAPP cytotoxicity. Structure-function studies identified a central region within 21-kDa 7B2 as important for this anti-aggregation effect.","method":"In vitro hIAPP fibrillation assays; cell viability assays; structure-function deletion analysis of 7B2 regions","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution plus cell assays, single lab, moderate structural detail","pmids":["24042052"],"is_preprint":false},{"year":1999,"finding":"7B2 protein is essential for targeting and activation of PC2 into the regulated secretory pathway: antisense suppression of 7B2 in rMTC 6-23 cells (~90% reduction) caused proPC2 to be constitutively released (not stored in secretory granules) and rendered it unable to process proNT/NN, without affecting proPC2 expression levels.","method":"Stable transfection with 7B2 antisense cDNA in endocrine rMTC 6-23 cells; immunoblotting; measurement of PC2 activity; pro-neurotensin processing assay; secretion pathway fractionation","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — antisense loss-of-function with specific sorting and processing readouts","pmids":["10198237"],"is_preprint":false},{"year":1998,"finding":"The oxyanion hole residue Asp309 in PC2 is critical for binding pro-7B2: the D309N mutation abolished pro-7B2 co-immunoprecipitation and significantly reduced PC2-mediated POMC processing to beta-endorphin. Similarly, Tyr194 participates in the interaction of PC2 with 7B2.","method":"Site-directed mutagenesis of PC2; vaccinia virus expression in AtT-20 and GH3 cells; co-immunoprecipitation; POMC processing assay (beta-endorphin production)","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — site-directed mutagenesis with functional binding and processing readouts","pmids":["9645470"],"is_preprint":false},{"year":1995,"finding":"Processed 7B2 (but not intact 27-kDa 7B2) can enhance in vitro POMC cleavage by PC2 in Xenopus intermediate pituitary cell lysates and with immunopurified Xenopus PC2; intact 7B2 abolished the enhancing effect (consistent with its known PC2 inhibitory activity), confirming that 7B2 displays chaperone/activating activity toward PC2.","method":"In vitro POMC cleavage assay in pituitary cell lysates; immunopurified PC2; addition of recombinant intact vs. processed 7B2 forms","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution assay, single lab, results consistent with larger body of work","pmids":["7672117"],"is_preprint":false},{"year":2009,"finding":"Pax6 transcription factor directly and indirectly (through cMaf and Beta2/NeuroD1) activates the 7B2 gene promoter in pancreatic alpha cells, thereby regulating 7B2 and PC2 expression and glucagon biosynthesis.","method":"siRNA knockdown of Pax6 in InR1G9 alpha cells; dominant-negative Pax6 expression; transactivation/binding studies at 7B2 and PC2 promoters","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transactivation and binding studies in cell lines, single lab","pmids":["19223471"],"is_preprint":false},{"year":2013,"finding":"Decreased 7B2•PC2 activity in hyp-mouse (XLH model) osteoblasts is central to pathogenesis: reduced 7B2 protein leads to impaired proPC2 activation, decreased FGF-23 cleavage, decreased active BMP1 (from decreased proBMP1 processing), increased DMP1, and elevated Fgf-23 mRNA/protein. Treatment with Hexa-D-Arginine increased 7B2•PC2 activity and rescued the HYP phenotype.","method":"Transfection of PC2 + 7B2 into murine osteoblasts; Sgne1 RNAi transfection; measurement of FGF-23, BMP1, DMP1; analysis of hyp-mouse bone (Sgne1 mRNA, 7B2 protein, proPC2 processing); Hexa-D-Arginine treatment of hyp-mice","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain- and loss-of-function in cells, supported by in vivo rescue experiment in disease mouse model","pmids":["22886699"],"is_preprint":false},{"year":2011,"finding":"7B2 dynamically modulates PC2-mediated peptide processing in a cell type-specific manner: in pancreatic alpha cells (α-TC6), 7B2 overexpression increased glucagon production and intracellular PC2 activity by routing PC2 to secretory granules; siRNA knockdown of 7B2 decreased glucagon. In contrast, 7B2 overexpression did not affect peptide production in anterior pituitary or beta cell lines despite increased PC2 secretion.","method":"Adenoviral overexpression of 7B2 in α-TC6 cells; siRNA knockdown; rescue of 7B2 in 7B2 null primary pituitary cultures; measurement of glucagon, α-MSH, and PC2 activity; in vivo glucagon measurement in 7B2-overexpressing cast/cast mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain- and loss-of-function across multiple cell types with in vivo corroboration","pmids":["22013069"],"is_preprint":false},{"year":2000,"finding":"Structure-function analysis of the 7B2 CT peptide showed that residues 3–18 are required for inhibitory potency; specific residues (Gln7, Gln9, Asp12) can be individually replaced by Ala without losing activity. All-D, all-L-inverso, and all-D analogues of CT peptide are completely inactive, indicating the main chain and side chains both interact with PC2. CT peptide inhibition requires a Lys-Lys pair for initial active-site binding.","method":"N-terminal truncation analysis; alanine scanning mutagenesis; stereo-isomer CT peptide analogues; competitive blockade with truncated peptides; in vitro PC2 inhibition assays","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic alanine scan and stereochemical probes with in vitro enzyme assay","pmids":["10673395"],"is_preprint":false},{"year":1990,"finding":"7B2 is a precursor molecule that is processed to an 18-kDa form in the carboxyl-terminal region in Xenopus intermediate lobe. The processed 18-kDa product (but not intact 7B2) is secreted in a regulated (dopamine-inhibitable) manner. Neither form is N-glycosylated.","method":"Pulse-chase immunoprecipitation analysis in Xenopus neurointermediate lobe; chemical and enzymatic peptide mapping; tunicamycin treatment; apomorphine inhibition of secretion","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pulse-chase with biochemical characterization, single model organism, foundational processing study","pmids":["2394742"],"is_preprint":false},{"year":1998,"finding":"The C. elegans 7B2 ortholog, despite only 23% sequence similarity to mammalian 7B2, retains both functional domains: the CT peptide inhibits vertebrate PC2 (IC50 130 nM) and the N-terminal domain facilitates proPC2 activation. The conserved PPNPCP motif and a heptapeptide in the CT region are identified as critical conserved functional elements.","method":"cDNA cloning; in vitro PC2 inhibition assays; two functional activation assays for N-terminal domain","journal":"DNA and cell biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro assays, single study, cross-species conservation of function demonstrated","pmids":["9726255"],"is_preprint":false},{"year":1986,"finding":"7B2 is localized within secretory granules of neuroendocrine cells (electron microscopy: small granules in gonadotrophs and thyrotrophs) and is co-released with catecholamines from bovine chromaffin cells upon nicotinic stimulation, indicating it undergoes regulated (exocytotic) secretion.","method":"Electron microscopy immunocytochemistry of pituitary cells; subcellular fractionation of chromaffin granules; RIA of 7B2 release from cultured bovine chromaffin cells stimulated with K+ and nicotine","journal":"Journal of neurochemistry / Cell and tissue research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct EM localization plus regulated secretion assay, foundational localization study","pmids":["3681297","3115588"],"is_preprint":false}],"current_model":"SCG5/7B2 is a bifunctional neuroendocrine secretory protein that acts as both a specific chaperone and an inhibitor of prohormone convertase 2 (PC2): its N-terminal domain (minimally a 36-residue segment containing a polyproline helix and disulfide bond) binds proPC2 in the ER in a Ca2+-dependent manner, stabilizes proPC2 against aggregation and unfolding, facilitates its transport to the TGN/secretory granules, and is absolutely required for generation of enzymatically active PC2; its C-terminal peptide (CT peptide, Ki ~57 nM) potently and specifically inhibits PC2 until PC2 itself cleaves the CT peptide at an internal Lys-Lys site with subsequent CPE trimming to terminate inhibition; phosphorylation of 7B2 at Ser115 by Golgi kinases inactivates its proPC2-activating function; and 7B2 also functions as a broader secretory anti-aggregation chaperone suppressing fibrillation of Aβ, α-synuclein, and IAPP in vitro and in neuronal cells."},"narrative":{"mechanistic_narrative":"SCG5/7B2 is a neuroendocrine secretory protein that functions as a dedicated, bifunctional partner of prohormone convertase 2 (PC2), coupling chaperone-assisted activation of PC2 with timed inhibition of its activity within the regulated secretory pathway [PMID:7913882, PMID:7790360, PMID:10089884]. Its N-terminal domain binds the proPC2 precursor specifically (not furin, PC1, PACE4, or PC5) in a Ca2+-dependent manner that does not require proPC2 glycosylation, acting after proPC2 has folded to stabilize it against unfolding and aggregation, escort it from the ER to the Golgi, and render it competent for activation at acidic pH [PMID:7722516, PMID:9348280, PMID:18467442]. A minimal 36-residue internal segment containing a polyproline-II helix, an adjacent alpha-helix, and the single disulfide bond carries all the information required for proPC2 activation, and interaction depends on PC2 catalytic-domain determinants including Tyr194, Asp309, and residues 242–248 [PMID:8798569, PMID:10409712, PMID:9422782, PMID:9645470, PMID:10799554]. The C-terminal CT peptide is a potent, PC2-specific inhibitor (Ki ~57 nM) requiring an internal Lys-Lys pair, and inhibition is self-terminating: PC2 cleaves the CT peptide at this Lys-Lys site followed by carboxypeptidase E trimming to abolish inhibitory potency [PMID:8016065, PMID:7782286, PMID:7727407, PMID:8643504, PMID:10673395]. Pro-7B2 is itself matured by furin-like cleavage at a pentabasic site in the TGN, a step required for PC2 to efficiently inactivate the CT peptide, while phosphorylation at Ser115 by Golgi kinases blocks proPC2 binding and inactivates the activating function [PMID:8034690, PMID:11677272, PMID:16286464]. 7B2 is absolutely required for PC2 activation in vivo, with 7B2-null mice showing no PC2 activity, defective islet hormone processing, and lethal Cushing's syndrome from intermediate-lobe ACTH hypersecretion [PMID:10089884, PMID:11854475]. Beyond PC2, 7B2 acts as a broader secretory anti-aggregation chaperone, suppressing fibrillation of Aβ, α-synuclein, and IAPP and protecting neuronal cells from their cytotoxicity [PMID:23172224, PMID:24042052].","teleology":[{"year":1986,"claim":"Established that 7B2 resides in neuroendocrine secretory granules and is released by regulated exocytosis, defining its subcellular setting before any enzymatic role was known.","evidence":"Immuno-EM of pituitary cells and stimulated catecholamine co-release from bovine chromaffin cells","pmids":["3681297","3115588"],"confidence":"Medium","gaps":["No molecular function assigned at this stage","Granule targeting determinants not defined"]},{"year":1990,"claim":"Identified 7B2 as a precursor processed at its C-terminus, with only the processed form secreted in a regulated manner, framing the precursor/product distinction central to its later dual functions.","evidence":"Pulse-chase immunoprecipitation and peptide mapping in Xenopus neurointermediate lobe","pmids":["2394742"],"confidence":"Medium","gaps":["Functional consequence of processing unknown","Processing enzyme not identified"]},{"year":1994,"claim":"Resolved 7B2's core dual identity: it specifically and transiently binds the proPC2 precursor as a chaperone while its intact form potently and selectively inhibits PC2 but not PC1/PC3.","evidence":"Co-IP and pulse-chase in pituitary/Xenopus cells plus in vitro inhibition assays with recombinant 7B2; furin-mediated TGN maturation of pro-7B2 also defined","pmids":["7913882","8016065","8034690"],"confidence":"High","gaps":["Domains responsible for each activity not yet mapped","Mechanism terminating inhibition unknown"]},{"year":1995,"claim":"Mapped the bifunctional architecture and kinetics: the C-terminal CT peptide (Ki ~57 nM, requiring a Lys171-Lys172 site) confers inhibition while the 21-kDa product facilitates proPC2 maturation, and proPC2 binding is Ca2+-dependent via the pro-7B2 pentabasic site.","evidence":"Stable transfection in multiple neuroendocrine lines, mutagenesis, fluorogenic inhibitor kinetics with purified PC2, calcium-chelation co-IP","pmids":["7790360","7722516","7782286","7727407","7672117"],"confidence":"High","gaps":["Structural basis of PPII/helix interaction not yet defined","Order of folding vs binding unresolved"]},{"year":1996,"claim":"Defined the N-terminal interaction surface and the inhibitory shutoff mechanism: a polyproline helix is required for proPC2 binding, and PC2 itself cleaves the CT peptide at an internal Lys-Lys site (with CPE trimming) to terminate inhibition.","evidence":"Proline point mutagenesis with four functional assays; in vitro CT peptide cleavage with purified PC2 plus CPE; thermal stabilization assays on purified PC2","pmids":["8798569","8643504","8660652","8681965"],"confidence":"High","gaps":["Precise sequence of dissociation vs maturation events partially unresolved","Atomic structure of complex absent"]},{"year":1997,"claim":"Clarified mechanism timing: proPC2 must fold before binding 7B2, after which 7B2 enables ER-to-Golgi transport and acidic-pH activation, reconstitutable in Golgi-enriched fractions.","evidence":"Pulse-chase, glycanase sensitivity, subcellular fractionation, and in vitro activation in Golgi fractions","pmids":["9348280"],"confidence":"High","gaps":["Conformational nature of the activation-competent state not structurally defined"]},{"year":1998,"claim":"Identified PC2 determinants of binding and proved in vivo necessity: PC2 proregion plus Tyr194 and Asp309 are required for 7B2 binding, and PC2-expressing cells lacking 7B2 contain only inactive proPC2 until rescued by 7B2.","evidence":"Domain-swap chimeras and point mutagenesis of PC2; stable 7B2 transfection rescue in PC2-expressing cells; hypoglycemic shock model","pmids":["9422782","9645470","9881669"],"confidence":"High","gaps":["Whether these residues form a contiguous binding epitope not structurally confirmed"]},{"year":1999,"claim":"Genetic ablation established 7B2 as absolutely required for PC2 activation in vivo and revealed PC2-independent endocrine functions, including a lethal ACTH hypersecretion phenotype, and the minimal 36-residue activation unit was defined.","evidence":"7B2 null mouse with hormonal/histological phenotyping versus PC2 null; sequential deletion/mutagenesis mapping the 36-residue activation core; antisense suppression in rMTC cells","pmids":["10089884","10409712","10198237"],"confidence":"High","gaps":["Molecular basis of PC2-independent pituitary functions unresolved","Secretory-granule sorting partner unknown"]},{"year":2000,"claim":"Refined the inhibitory and binding interfaces: CT peptide residues 3–18 with a Lys-Lys pair and both main- and side-chain contacts drive inhibition, and PC2 residues 242–248 govern 7B2 binding and CT-peptide inhibition.","evidence":"Alanine scanning and stereo-isomer CT analogues; PC2 catalytic-domain mutagenesis with binding and processing readouts","pmids":["10673395","10799554"],"confidence":"High","gaps":["No co-crystal structure of CT peptide bound to PC2 active site"]},{"year":2001,"claim":"Connected pro-7B2 maturation to inhibition control: furin cleavage of the pentabasic site is needed to produce PC2 capable of efficiently inactivating the CT peptide, decoupling activation from inhibitor turnover.","evidence":"CT-peptide and furin-site mutants tested in cell-free activation and HEK293 transfection assays","pmids":["11677272"],"confidence":"High","gaps":["Structural reason furin cleavage gates CT inactivation unclear"]},{"year":2002,"claim":"Mechanistically linked the 7B2-null lethality to a dopaminergic deficiency: reduced pituitary dopamine drives ACTH/corticosterone excess, and adrenalectomy rescues survival.","evidence":"Adrenalectomy rescue of 7B2 null mice with ACTH, corticosterone, and dopamine measurements","pmids":["11854475"],"confidence":"High","gaps":["How 7B2 loss lowers pituitary dopamine mechanistically not resolved"]},{"year":2005,"claim":"Revealed phospho-regulation: Golgi-kinase phosphorylation at Ser115 abolishes proPC2 binding and activation, providing a post-translational off-switch for the chaperone function.","evidence":"32P labeling, phosphoamino acid analysis, Ser115 mutagenesis, co-IP, and cell-free activation assays","pmids":["16286464"],"confidence":"High","gaps":["Identity of the responsible Golgi kinase not pinned down","Physiological trigger for phosphorylation unknown"]},{"year":2008,"claim":"Demonstrated 7B2 acts as an anti-aggregation chaperone toward proPC2 itself, solubilizing oligomers and maintaining an activation-competent conformation.","evidence":"Cross-linking, sucrose gradients, velocity sedimentation, and exogenous recombinant 7B2 addition to proPC2-expressing cells","pmids":["18467442"],"confidence":"High","gaps":["Whether anti-aggregation and activation are separable activities unresolved"]},{"year":2011,"claim":"Showed 7B2 modulates PC2-mediated processing in a cell-type-specific manner, notably boosting glucagon production in alpha cells by routing PC2 to secretory granules.","evidence":"Adenoviral overexpression and siRNA knockdown across alpha, beta, and pituitary cells with in vivo glucagon corroboration","pmids":["22013069"],"confidence":"High","gaps":["Basis of cell-type specificity not defined"]},{"year":2012,"claim":"Broadened 7B2's chaperone role beyond PC2 to general amyloid suppression, blocking Aβ and α-synuclein fibrillation and cytotoxicity and co-localizing with disease deposits.","evidence":"In vitro ThT fibrillation assays, gain/loss-of-function in Neuro-2A cells, and immunofluorescence in mouse and human brain","pmids":["23172224"],"confidence":"High","gaps":["In vivo significance of anti-amyloid activity unestablished","Region mediating broad chaperone activity not mapped"]},{"year":2013,"claim":"Extended the anti-aggregation activity to IAPP and tied reduced 7B2•PC2 activity to X-linked hypophosphatemia pathogenesis, with pharmacological rescue in the hyp-mouse.","evidence":"In vitro hIAPP fibrillation and cell-protection assays with deletion mapping; osteoblast gain/loss-of-function and Hexa-D-Arginine rescue in hyp-mice","pmids":["24042052","22886699"],"confidence":"High","gaps":["Whether anti-aggregation contributes to bone phenotype unclear","Generality of disease relevance not established"]},{"year":null,"claim":"The atomic structure of the 7B2–proPC2 complex and the molecular basis of 7B2's PC2-independent and broad anti-amyloid functions remain to be resolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No co-crystal/cryo-EM structure of the chaperone or inhibitory complex","PC2-independent endocrine roles mechanistically undefined","Physiological role of broad anti-aggregation activity in vivo unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,4,5,16,30]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,5,8,30]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,21,22,23]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[21,22,23]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,3,9]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[7,9,20]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[33,8,24]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,2,9,13]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[9,24,29]}],"complexes":[],"partners":["PCSK2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P05408","full_name":"Neuroendocrine protein 7B2","aliases":["Pituitary polypeptide","Secretogranin V","Secretogranin-5","Secretory granule endocrine protein I"],"length_aa":212,"mass_kda":23.7,"function":"Acts as a molecular chaperone for PCSK2/PC2, preventing its premature activation in the regulated secretory pathway. 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Development and characterization of a panel of monoclonal antibodies against the 7B2 neuroendocrine protein.","date":"1991","source":"Journal of immunological methods","url":"https://pubmed.ncbi.nlm.nih.gov/1717598","citation_count":21,"is_preprint":false},{"pmid":"12472887","id":"PMC_12472887","title":"Increased synthesis but decreased processing of neuronal proCCK in prohormone convertase 2 and 7B2 knockout animals.","date":"2002","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12472887","citation_count":21,"is_preprint":false},{"pmid":"1752059","id":"PMC_1752059","title":"The secretory granule peptides 7B2 and CCB are sensitive biochemical markers of neuro-endocrine bronchial tumours in man.","date":"1991","source":"Clinical endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/1752059","citation_count":20,"is_preprint":false},{"pmid":"10673395","id":"PMC_10673395","title":"Structure-function analysis of the 7B2 CT peptide.","date":"2000","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/10673395","citation_count":20,"is_preprint":false},{"pmid":"7794252","id":"PMC_7794252","title":"The neuroendocrine protein 7B2 acts as a molecular chaperone in the in vitro folding of human insulin-like growth factor-1 secreted from yeast.","date":"1995","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/7794252","citation_count":20,"is_preprint":false},{"pmid":"7824189","id":"PMC_7824189","title":"Pan-neuronal mRNA expression of the secretory polypeptide 7B2.","date":"1994","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/7824189","citation_count":19,"is_preprint":false},{"pmid":"3944535","id":"PMC_3944535","title":"A novel pituitary protein (7B2)-like immunoreactivity is secreted by a rat phaeochromocytoma cell line (PC12).","date":"1986","source":"The Journal of endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/3944535","citation_count":19,"is_preprint":false},{"pmid":"12021197","id":"PMC_12021197","title":"The lethal form of Cushing's in 7B2 null mice is caused by multiple metabolic and hormonal abnormalities.","date":"2002","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/12021197","citation_count":19,"is_preprint":false},{"pmid":"7505408","id":"PMC_7505408","title":"Expression of neuroendocrine secretory protein 7B2 mRNA in the mouse and rat pituitary gland.","date":"1993","source":"Neuroendocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/7505408","citation_count":18,"is_preprint":false},{"pmid":"8617287","id":"PMC_8617287","title":"Structural organization of the gene encoding the neuroendocrine chaperone 7B2.","date":"1996","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8617287","citation_count":18,"is_preprint":false},{"pmid":"17334394","id":"PMC_17334394","title":"SGNE1/7B2 is epigenetically altered and transcriptionally downregulated in human medulloblastomas.","date":"2007","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/17334394","citation_count":17,"is_preprint":false},{"pmid":"18439298","id":"PMC_18439298","title":"Overexpression of Scg5 increases enzymatic activity of PCSK2 and is inversely correlated with body weight in congenic mice.","date":"2008","source":"BMC genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18439298","citation_count":17,"is_preprint":false},{"pmid":"1466150","id":"PMC_1466150","title":"Studies on co-localization of 7B2 and pancreatic hormones in normal and tumoural islet cells.","date":"1992","source":"Virchows Archiv. 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An immunocytochemical and in situ hybridization study.","date":"1991","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/1652364","citation_count":14,"is_preprint":false},{"pmid":"3400405","id":"PMC_3400405","title":"7B2, a new protein secreted by human functionless pituitary tumours, in vitro.","date":"1988","source":"Acta endocrinologica","url":"https://pubmed.ncbi.nlm.nih.gov/3400405","citation_count":14,"is_preprint":false},{"pmid":"1424185","id":"PMC_1424185","title":"Expression of the neuroendocrine cell marker 7B2 in human ACTH secreting tumours.","date":"1992","source":"Clinical endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/1424185","citation_count":13,"is_preprint":false},{"pmid":"10799554","id":"PMC_10799554","title":"Mutations in the catalytic domain of prohormone convertase 2 result in decreased binding to 7B2 and loss of inhibition with 7B2 C-terminal peptide.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10799554","citation_count":13,"is_preprint":false},{"pmid":"3903556","id":"PMC_3903556","title":"Immunoreactivity of vasopressin and a novel pituitary protein '7B2' in Long-Evans and Brattleboro rat hypothalamus and hypophysis.","date":"1985","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/3903556","citation_count":13,"is_preprint":false},{"pmid":"34791022","id":"PMC_34791022","title":"Association Between Maternal Adverse Childhood Experiences and Neonatal SCG5 DNA Methylation-Effect Modification by Prenatal Home Visiting.","date":"2022","source":"American journal of epidemiology","url":"https://pubmed.ncbi.nlm.nih.gov/34791022","citation_count":12,"is_preprint":false},{"pmid":"14709802","id":"PMC_14709802","title":"Regulation of cell growth and expression of 7B2, PC2, and PC1/3 by TGFbeta 1 and sodium butyrate in a human pituitary cell line (HP75).","date":"2003","source":"Endocrine","url":"https://pubmed.ncbi.nlm.nih.gov/14709802","citation_count":12,"is_preprint":false},{"pmid":"29960146","id":"PMC_29960146","title":"Highly deleterious variations in COX1, CYTB, SCG5, FK2, PRL and PGF genes are the potential adaptation of the immigrated African ostrich population.","date":"2018","source":"Computers in biology and medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29960146","citation_count":12,"is_preprint":false},{"pmid":"27984123","id":"PMC_27984123","title":"Clinicopathological features of a kindred with SCG5-GREM1-associated hereditary mixed polyposis syndrome.","date":"2016","source":"Human pathology","url":"https://pubmed.ncbi.nlm.nih.gov/27984123","citation_count":11,"is_preprint":false},{"pmid":"8680421","id":"PMC_8680421","title":"Depolarizing action of secretory granule protein 7B2 on rat supraoptic neurosecretory neurons.","date":"1993","source":"Journal of neuroendocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/8680421","citation_count":11,"is_preprint":false},{"pmid":"16286464","id":"PMC_16286464","title":"Neuroendocrine protein 7B2 can be inactivated by phosphorylation within the secretory pathway.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16286464","citation_count":11,"is_preprint":false},{"pmid":"22013069","id":"PMC_22013069","title":"Dynamic modulation of prohormone convertase 2 (PC2)-mediated precursor processing by 7B2 protein: preferential effect on glucagon synthesis.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22013069","citation_count":11,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":49917,"output_tokens":9399,"usd":0.145368,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":19287,"output_tokens":5147,"usd":0.112555,"stage2_stop_reason":"end_turn"},"total_usd":0.257923,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1994,\n      \"finding\": \"7B2 (SCG5) acts as a neuroendocrine chaperone that specifically associates with the precursor form of prohormone convertase PC2 (proPC2) in the early secretory pathway; the interaction is transient, commencing in the ER and dissociating in later compartments coincident with cleavages of 7B2, proPC2, and prohormone. The amino-terminal half of 7B2 is distantly related to chaperonins.\",\n      \"method\": \"In vitro incubation with recombinant 7B2 and newly synthesized pituitary proteins; metabolic cell labeling and co-immunoprecipitation; pulse-chase analysis in Xenopus intermediate lobe cells\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal co-IP, pulse-chase, in vitro binding assay; independently confirmed by multiple subsequent studies\",\n      \"pmids\": [\"7913882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Intact recombinant 7B2 is a potent, specific inhibitor of PC2 enzymatic activity in vitro but does not inhibit the related convertase PC1/PC3. The 7B2 cleavage product (C-terminal half removed) is virtually inactive as an inhibitor. The carboxyl-terminal half of 7B2 is distantly related to the potato inhibitor I family of subtilisin inhibitors.\",\n      \"method\": \"In vitro enzyme inhibition assays using recombinant 7B2 against PC2 and PC1/PC3; sequence homology analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution assay with recombinant proteins; replicated in multiple subsequent studies\",\n      \"pmids\": [\"8016065\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Overexpression of 21-kDa 7B2 (the naturally occurring maturation product of 27-kDa pro-7B2) greatly facilitates the kinetics of proPC2 maturation and is required for the generation of enzymatic activity; the N-terminal 'chaperone' domain alone was insufficient. PC2 enzymatic activity was inhibited by the 7B2 carboxyl-terminal peptide, confirming specificity.\",\n      \"method\": \"Stable transfection of neuroendocrine cell lines (AtT-20/PC2, Rin5f, CHO/PC2) with 7B2 constructs; pulse-chase metabolic labeling; fluorogenic substrate enzyme activity assay; inhibition by 7B2 CT peptide\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro activity assay, multiple cell lines, domain mutagenesis; replicated by other labs\",\n      \"pmids\": [\"7790360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Within the ER, pro-7B2 specifically binds proPC2 but not other convertases (furin, PC1, PACE4, PC5). This binding is Ca2+-dependent and does not require N-glycosylation of proPC2. Mutagenesis of the pentabasic RRKRRS site in pro-7B2 (critical residues R152, R151, S156) abolished or greatly diminished binding. After furin cleavage in the TGN, 7B2 remains bound to PC2, suggesting a second Ca2+-dependent binding site.\",\n      \"method\": \"Biosynthetic pulse-chase analysis; co-immunoprecipitation; site-directed mutagenesis of pro-7B2; calcium chelation experiments in neuroendocrine cells\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP with mutagenesis, multiple orthogonal methods, replicated across labs\",\n      \"pmids\": [\"7722516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The carboxyl-terminal portion of 7B2 (CT peptide, residues ~155–185) is responsible for PC2 inhibition. A short segment containing a Lys171-Lys172 dibasic site is critical; single and double mutations at this site strongly diminished or abolished inhibitory potency. No 7B2 mutant inhibited PC1/PC3.\",\n      \"method\": \"In vitro mutagenesis; prokaryotic expression of mutant 7B2 proteins; in vitro enzyme activity assays against PC1/PC3 and PC2\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis, multiple truncation and point mutants tested\",\n      \"pmids\": [\"7782286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Immunopurified PC2 cleaves the fluorogenic substrate Cbz-Arg-Ser-Lys-Arg-AMC in a Ca2+-dependent manner (half-maximal stimulation at 75 µM Ca2+, pH optimum 5.0). The 27-kDa 7B2 is a tight-binding inhibitor of PC2 with Kd = 7.3 nM. The 7B2 CT peptide (residues ~155–185) is a potent inhibitor (Ki = 57 nM) and can block PC2-mediated proenkephalin processing; 21-kDa 7B2 is functionally inactive as a proteinase inhibitor.\",\n      \"method\": \"Immunopurification of PC2 from mouse insulinoma cell conditioned medium; fluorogenic substrate assay; inhibitor kinetics with recombinant 27-kDa 7B2 and synthetic CT peptides; in vitro cleavage of recombinant proenkephalin\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic characterization with purified components, Ki and Kd quantification\",\n      \"pmids\": [\"7727407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Active recombinant PC2 was purified to homogeneity from conditioned medium of CHO cells co-expressing PC2 and 21-kDa 7B2. 21-kDa 7B2 copurifies with activated PC2 and provides significant stabilization against thermal denaturation in a Ca2+- and pH-dependent manner (optimal at millimolar Ca2+, pH 5–6), consistent with a role for 7B2 in stabilizing PC2 activity within secretory granules.\",\n      \"method\": \"Purification of recombinant PC2; thermal denaturation assays; enzyme activity assays; gel filtration to remove associated 7B2 followed by re-addition\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified components, multiple orthogonal activity and stability assays\",\n      \"pmids\": [\"8660652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Pro-7B2 is tyrosine-sulfated in the trans-Golgi network and cleaved by a furin-like convertase at the RXKR/RRKRR site within the TGN to generate the 23-kDa form; PC1 and PC2 cannot process pro-7B2. Protein transport to Golgi compartments is required for this processing (blocked by monensin, brefeldin A, or low temperature).\",\n      \"method\": \"Recombinant vaccinia virus expression in multiple cell lines (AtT-20, PC12, GH4C1, Ltk-); mutagenesis of P4 Arg; co-expression with PC1, PC2, furin; expression in furin-deficient LoVo cells; [35S]SO4 pulse-chase; monensin/brefeldin A treatments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple cell lines, furin-deficient cells, site-directed mutagenesis, pharmacological inhibitors\",\n      \"pmids\": [\"8034690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PC2 itself cleaves the 7B2 CT peptide at an internal Lys-Lys site in secretory granules; the resulting cleavage product is non-inhibitory after removal of terminal lysines by carboxypeptidase E (CPE). This provides a mechanism for intracellular inactivation of the CT peptide inhibitor.\",\n      \"method\": \"Metabolic labeling ([3H]valine) and immunoprecipitation in multiple cell lines; RIA against CT peptide carboxyl terminus; in vitro incubation of 125I-CT peptide with purified recombinant PC2; synthetic CT peptide derivative inhibitory assays; inclusion of CPE in reactions\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified PC2, multiple cell lines, corroborated by RIA and activity assays\",\n      \"pmids\": [\"8643504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"7B2 does not promote early proPC2 folding; instead, proPC2 must fold before it can bind 7B2. Once bound, 7B2 facilitates proPC2 transport from the ER to the Golgi and is required for proPC2 activation at acidic pH. ProPC2 activation could be reconstituted in Golgi-enriched subcellular fractions in vitro and required 7B2.\",\n      \"method\": \"Pulse-chase labeling; N-glycanase F sensitivity assay; inhibition of proPC2 folding experiments; co-immunoprecipitation; subcellular fractionation; in vitro proPC2 activation assay in Golgi-enriched fractions\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — subcellular fractionation, in vitro reconstitution in Golgi fractions, multiple orthogonal methods\",\n      \"pmids\": [\"9348280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"A polyproline helix-like (PPII) structure within the N-terminal domain of 7B2 (around Pro90, Pro91, Pro93, Pro95) is required for interaction with proPC2. Point mutagenesis of critical prolines severely impaired or abolished 7B2 bioactivity as measured by four assays: co-immunoprecipitation with proPC2, facilitation of proPC2 maturation, acquisition of PC2 enzymatic activity, and thermal protection of PC2. An adjacent predicted alpha-helix (residues 107–123) also contributes.\",\n      \"method\": \"Site-directed point mutagenesis; co-immunoprecipitation; proPC2 maturation assay; PC2 enzymatic activity assay; thermal protection assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis with four independent functional assays in the same study\",\n      \"pmids\": [\"8798569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The PC2 proregion is required but not sufficient for 7B2 binding; the P domain stabilizes PC2 structure and is not interchangeable with PC1's P domain; the C-terminal domain is not involved in 7B2 binding. A single residue in the PC2 catalytic domain, Tyr-194, is required for 7B2 binding and proPC2 activation; Y194 is located within a surface-exposed loop rich in aromatic amino acids.\",\n      \"method\": \"Sequential domain deletions, site-directed mutagenesis, and PC2/PC1 domain-swapping chimeras expressed in AtT-20 cells; co-immunoprecipitation; maturation assay; enzymatic activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — systematic domain swapping and point mutagenesis with multiple functional readouts\",\n      \"pmids\": [\"9422782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"7B2 is essential for proteolytic conversion and activation of proPC2 in vivo: cells expressing PC2 but not 7B2 (SK-N-MCIXC neuroepithelioma) contain only inactive proPC2 forms; stable transfection with pro-7B2 rescued secretion of mature, active 68-kDa PC2. In a model of hypoglycemic shock, decreased adrenomedullary 7B2 expression correlated with increased proPC2:PC2 ratio.\",\n      \"method\": \"Immunoblotting of cell fractions; stable transfection of 7B2 cDNA into PC2-expressing cells; insulin-induced hypoglycemic shock animal model; comparison of developing rat brain PC2 forms\",\n      \"journal\": \"DNA and cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple in vivo and cell-based models converging on same conclusion; replicated finding\",\n      \"pmids\": [\"9881669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"7B2 null mice have no demonstrable PC2 activity, are deficient in processing islet hormones (hyperproinsulinemia, hypoglucagonemia), and develop lethal Cushing's syndrome from pituitary intermediate lobe ACTH hypersecretion. This establishes that 7B2 is absolutely required for PC2 activation in vivo and has additional functions in regulating pituitary hormone secretion beyond PC2.\",\n      \"method\": \"7B2 null mouse (knockout via transposon-facilitated technique); comparison with PC2 null phenotype; measurement of circulating hormones (ACTH, corticosterone, insulin, glucagon); histology\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with specific phenotypic readouts, comparison to PC2 null, replicated\",\n      \"pmids\": [\"10089884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"A minimal 36-residue internal peptide of 7B2 (containing the proline-rich sequence, an alpha-helix, and the only disulfide bond) contains all information required for proPC2 activation. Mutation of the alpha-helix or the cysteines forming the disulfide bond abolished proPC2 activation activity.\",\n      \"method\": \"Sequential deletions of 7B2; mutagenesis of alpha-helix and cysteine residues; four functional assays: proPC2 binding, maturation facilitation, in vivo and in vitro proPC2 activation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic deletion mapping and mutagenesis with multiple orthogonal assays\",\n      \"pmids\": [\"10409712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Dissociation of the N-terminal 7B2 fragment from proPC2 precedes (and is not directly linked to) proPC2 maturation; proPC2 maturation does not occur while associated with intact 7B2 precursor. The C-terminal region of 7B2 is necessary and sufficient for inhibition of proPC2 conversion in vitro.\",\n      \"method\": \"Pulse-chase analysis in Xenopus and mouse intermediate pituitary cells; in vitro conversion assay with recombinant 7B2 and truncation mutants\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — cell-based pulse-chase and in vitro reconstitution with deletion mutants\",\n      \"pmids\": [\"8681965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Residues 242–248 in the PC2 catalytic domain (PC2-specific sequence) are required for binding to 21-kDa 7B2 and for inhibition by the 7B2 CT peptide; replacement with corresponding PC1 residues greatly reduced 7B2 binding and nearly abolished CT peptide inhibition, without profoundly altering substrate cleavage specificity.\",\n      \"method\": \"Site-directed mutagenesis of PC2 catalytic domain; co-immunoprecipitation with 7B2; in vivo proenkephalin and POMC cleavage assays; in vitro fluorogenic substrate assay; CT peptide inhibition assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis with multiple functional readouts\",\n      \"pmids\": [\"10799554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Drosophila 7B2 (d7B2) and rat 7B2 can both support dPC2 (amontillado) secretion and activity in Drosophila S2 insect cells but not in HEK-293 cells, demonstrating that dPC2 requires insect cell-specific posttranslational processing events for maturation and secretion, and that 7B2–PC2 interaction is evolutionarily conserved.\",\n      \"method\": \"Transfection of dPC2 and d7B2/r7B2 cDNAs into HEK-293 and S2 cells; PC2 activity assays; immunoblotting; pulse-chase labeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two cell systems compared, enzymatic activity and immunoblot, single study\",\n      \"pmids\": [\"10749852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Cleavage at the 7B2 furin consensus pentabasic site is required for production of PC2 capable of efficiently cleaving the inhibitory CT peptide. When the furin site is blocked (blockade mutant), intact 27-kDa 7B2 accumulates and PC2 secreted with it lacks ability to inactivate the CT peptide, although proPC2 activation per se does not require furin cleavage when the CT peptide is non-inhibitory.\",\n      \"method\": \"Construction of 7B2 mutants (CT peptide KK→SS; furin site blockade; double mutant); cell-free proPC2 activation assay; transient transfection into HEK293 cells; measurement of PC2 activity and CT peptide forms in conditioned medium\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — cell-free reconstitution plus cell-based transfection, multiple mutants, single rigorous study\",\n      \"pmids\": [\"11677272\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Mortality in 7B2 null mice is caused by elevated corticosterone secondary to ACTH hypersecretion; adrenalectomy rescues survival and normalizes pituitary dopamine (which is reduced to ~25% of WT in 7B2 nulls), circulating ACTH, and corticosterone. This indicates a 7B2-mediated dopaminergic deficiency contributes to ACTH hypersecretion.\",\n      \"method\": \"Adrenalectomy of 7B2 null mice; measurement of circulating ACTH, corticosterone, pituitary dopamine; comparison with PC2 null mice\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic null rescue experiment with hormonal and neurochemical readouts\",\n      \"pmids\": [\"11854475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"7B2 can be phosphorylated at Ser115 (and additional serine/threonine residues) by Golgi kinases in Rin cells and chromaffin cells but not AtT-20 cells. Phosphorylated 7B2 is unable to bind proPC2 (co-immunoprecipitation) and is impaired in facilitating proPC2 activation (cell-free assay), functionally inactivating it in a manner analogous to BiP phosphorylation.\",\n      \"method\": \"Metabolic 32P labeling; phosphoamino acid analysis; site-directed mutagenesis of Ser115; co-immunoprecipitation of phospho-7B2 with proPC2; cell-free proPC2 activation assay; in vitro Golgi kinase phosphorylation with kinase inhibitors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis confirming phosphorylation site, two independent functional assays, in vitro kinase identification\",\n      \"pmids\": [\"16286464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"7B2 possesses chaperone activity that prevents unfolding and aggregation of proPC2; addition of exogenous recombinant 7B2 to CHO cells expressing proPC2 prevented secreted PC2 aggregation in a dose-dependent manner. Intracellular proPC2 exists in part as higher-order oligomers, reduced by co-expressed 7B2. Velocity sedimentation showed 7B2 solubilizes three PC2 species from precipitable aggregates. An activation-competent PC2 conformation cannot be maintained without 7B2.\",\n      \"method\": \"Aggregation assays; enzymatic activity assays; chemical cross-linking; sucrose density gradients; velocity sedimentation; addition of exogenous recombinant 7B2 to cells\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal biophysical and biochemical methods in single study\",\n      \"pmids\": [\"18467442\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"7B2 suppresses fibrillation and aggregation of Aβ(1-42), Aβ(1-40), and α-synuclein in vitro at 1:10 molar ratio. In Neuro-2A cell culture, extracellular or adenovirally overexpressed 7B2 blocked neurocytotoxicity of Aβ(1-42) and increased cell viability; RNAi knockdown of 7B2 increased Aβ(1-42)-induced cytotoxicity. In APP/PSEN1 mouse brains and human AD/PD brains, 7B2 co-localizes with Aβ plaques and α-synuclein deposits.\",\n      \"method\": \"In vitro fibrillation/aggregation assays (ThT fluorescence); adenoviral overexpression; RNAi knockdown; cell viability assays; immunofluorescence co-localization in mouse model and human postmortem brain\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro reconstitution with gain- and loss-of-function cell studies plus in vivo co-localization\",\n      \"pmids\": [\"23172224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"21-kDa 7B2 blocks hIAPP (islet amyloid polypeptide) fibrillation in vitro and protects Rin5f cells from hIAPP cytotoxicity. Structure-function studies identified a central region within 21-kDa 7B2 as important for this anti-aggregation effect.\",\n      \"method\": \"In vitro hIAPP fibrillation assays; cell viability assays; structure-function deletion analysis of 7B2 regions\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution plus cell assays, single lab, moderate structural detail\",\n      \"pmids\": [\"24042052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"7B2 protein is essential for targeting and activation of PC2 into the regulated secretory pathway: antisense suppression of 7B2 in rMTC 6-23 cells (~90% reduction) caused proPC2 to be constitutively released (not stored in secretory granules) and rendered it unable to process proNT/NN, without affecting proPC2 expression levels.\",\n      \"method\": \"Stable transfection with 7B2 antisense cDNA in endocrine rMTC 6-23 cells; immunoblotting; measurement of PC2 activity; pro-neurotensin processing assay; secretion pathway fractionation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — antisense loss-of-function with specific sorting and processing readouts\",\n      \"pmids\": [\"10198237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The oxyanion hole residue Asp309 in PC2 is critical for binding pro-7B2: the D309N mutation abolished pro-7B2 co-immunoprecipitation and significantly reduced PC2-mediated POMC processing to beta-endorphin. Similarly, Tyr194 participates in the interaction of PC2 with 7B2.\",\n      \"method\": \"Site-directed mutagenesis of PC2; vaccinia virus expression in AtT-20 and GH3 cells; co-immunoprecipitation; POMC processing assay (beta-endorphin production)\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — site-directed mutagenesis with functional binding and processing readouts\",\n      \"pmids\": [\"9645470\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Processed 7B2 (but not intact 27-kDa 7B2) can enhance in vitro POMC cleavage by PC2 in Xenopus intermediate pituitary cell lysates and with immunopurified Xenopus PC2; intact 7B2 abolished the enhancing effect (consistent with its known PC2 inhibitory activity), confirming that 7B2 displays chaperone/activating activity toward PC2.\",\n      \"method\": \"In vitro POMC cleavage assay in pituitary cell lysates; immunopurified PC2; addition of recombinant intact vs. processed 7B2 forms\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution assay, single lab, results consistent with larger body of work\",\n      \"pmids\": [\"7672117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Pax6 transcription factor directly and indirectly (through cMaf and Beta2/NeuroD1) activates the 7B2 gene promoter in pancreatic alpha cells, thereby regulating 7B2 and PC2 expression and glucagon biosynthesis.\",\n      \"method\": \"siRNA knockdown of Pax6 in InR1G9 alpha cells; dominant-negative Pax6 expression; transactivation/binding studies at 7B2 and PC2 promoters\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transactivation and binding studies in cell lines, single lab\",\n      \"pmids\": [\"19223471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Decreased 7B2•PC2 activity in hyp-mouse (XLH model) osteoblasts is central to pathogenesis: reduced 7B2 protein leads to impaired proPC2 activation, decreased FGF-23 cleavage, decreased active BMP1 (from decreased proBMP1 processing), increased DMP1, and elevated Fgf-23 mRNA/protein. Treatment with Hexa-D-Arginine increased 7B2•PC2 activity and rescued the HYP phenotype.\",\n      \"method\": \"Transfection of PC2 + 7B2 into murine osteoblasts; Sgne1 RNAi transfection; measurement of FGF-23, BMP1, DMP1; analysis of hyp-mouse bone (Sgne1 mRNA, 7B2 protein, proPC2 processing); Hexa-D-Arginine treatment of hyp-mice\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain- and loss-of-function in cells, supported by in vivo rescue experiment in disease mouse model\",\n      \"pmids\": [\"22886699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"7B2 dynamically modulates PC2-mediated peptide processing in a cell type-specific manner: in pancreatic alpha cells (α-TC6), 7B2 overexpression increased glucagon production and intracellular PC2 activity by routing PC2 to secretory granules; siRNA knockdown of 7B2 decreased glucagon. In contrast, 7B2 overexpression did not affect peptide production in anterior pituitary or beta cell lines despite increased PC2 secretion.\",\n      \"method\": \"Adenoviral overexpression of 7B2 in α-TC6 cells; siRNA knockdown; rescue of 7B2 in 7B2 null primary pituitary cultures; measurement of glucagon, α-MSH, and PC2 activity; in vivo glucagon measurement in 7B2-overexpressing cast/cast mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain- and loss-of-function across multiple cell types with in vivo corroboration\",\n      \"pmids\": [\"22013069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Structure-function analysis of the 7B2 CT peptide showed that residues 3–18 are required for inhibitory potency; specific residues (Gln7, Gln9, Asp12) can be individually replaced by Ala without losing activity. All-D, all-L-inverso, and all-D analogues of CT peptide are completely inactive, indicating the main chain and side chains both interact with PC2. CT peptide inhibition requires a Lys-Lys pair for initial active-site binding.\",\n      \"method\": \"N-terminal truncation analysis; alanine scanning mutagenesis; stereo-isomer CT peptide analogues; competitive blockade with truncated peptides; in vitro PC2 inhibition assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic alanine scan and stereochemical probes with in vitro enzyme assay\",\n      \"pmids\": [\"10673395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"7B2 is a precursor molecule that is processed to an 18-kDa form in the carboxyl-terminal region in Xenopus intermediate lobe. The processed 18-kDa product (but not intact 7B2) is secreted in a regulated (dopamine-inhibitable) manner. Neither form is N-glycosylated.\",\n      \"method\": \"Pulse-chase immunoprecipitation analysis in Xenopus neurointermediate lobe; chemical and enzymatic peptide mapping; tunicamycin treatment; apomorphine inhibition of secretion\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pulse-chase with biochemical characterization, single model organism, foundational processing study\",\n      \"pmids\": [\"2394742\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The C. elegans 7B2 ortholog, despite only 23% sequence similarity to mammalian 7B2, retains both functional domains: the CT peptide inhibits vertebrate PC2 (IC50 130 nM) and the N-terminal domain facilitates proPC2 activation. The conserved PPNPCP motif and a heptapeptide in the CT region are identified as critical conserved functional elements.\",\n      \"method\": \"cDNA cloning; in vitro PC2 inhibition assays; two functional activation assays for N-terminal domain\",\n      \"journal\": \"DNA and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro assays, single study, cross-species conservation of function demonstrated\",\n      \"pmids\": [\"9726255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"7B2 is localized within secretory granules of neuroendocrine cells (electron microscopy: small granules in gonadotrophs and thyrotrophs) and is co-released with catecholamines from bovine chromaffin cells upon nicotinic stimulation, indicating it undergoes regulated (exocytotic) secretion.\",\n      \"method\": \"Electron microscopy immunocytochemistry of pituitary cells; subcellular fractionation of chromaffin granules; RIA of 7B2 release from cultured bovine chromaffin cells stimulated with K+ and nicotine\",\n      \"journal\": \"Journal of neurochemistry / Cell and tissue research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct EM localization plus regulated secretion assay, foundational localization study\",\n      \"pmids\": [\"3681297\", \"3115588\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SCG5/7B2 is a bifunctional neuroendocrine secretory protein that acts as both a specific chaperone and an inhibitor of prohormone convertase 2 (PC2): its N-terminal domain (minimally a 36-residue segment containing a polyproline helix and disulfide bond) binds proPC2 in the ER in a Ca2+-dependent manner, stabilizes proPC2 against aggregation and unfolding, facilitates its transport to the TGN/secretory granules, and is absolutely required for generation of enzymatically active PC2; its C-terminal peptide (CT peptide, Ki ~57 nM) potently and specifically inhibits PC2 until PC2 itself cleaves the CT peptide at an internal Lys-Lys site with subsequent CPE trimming to terminate inhibition; phosphorylation of 7B2 at Ser115 by Golgi kinases inactivates its proPC2-activating function; and 7B2 also functions as a broader secretory anti-aggregation chaperone suppressing fibrillation of Aβ, α-synuclein, and IAPP in vitro and in neuronal cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SCG5/7B2 is a neuroendocrine secretory protein that functions as a dedicated, bifunctional partner of prohormone convertase 2 (PC2), coupling chaperone-assisted activation of PC2 with timed inhibition of its activity within the regulated secretory pathway [#0, #2, #13]. Its N-terminal domain binds the proPC2 precursor specifically (not furin, PC1, PACE4, or PC5) in a Ca2+-dependent manner that does not require proPC2 glycosylation, acting after proPC2 has folded to stabilize it against unfolding and aggregation, escort it from the ER to the Golgi, and render it competent for activation at acidic pH [#3, #9, #21]. A minimal 36-residue internal segment containing a polyproline-II helix, an adjacent alpha-helix, and the single disulfide bond carries all the information required for proPC2 activation, and interaction depends on PC2 catalytic-domain determinants including Tyr194, Asp309, and residues 242\\u2013248 [#10, #14, #11, #25, #16]. The C-terminal CT peptide is a potent, PC2-specific inhibitor (Ki ~57 nM) requiring an internal Lys-Lys pair, and inhibition is self-terminating: PC2 cleaves the CT peptide at this Lys-Lys site followed by carboxypeptidase E trimming to abolish inhibitory potency [#1, #4, #5, #8, #30]. Pro-7B2 is itself matured by furin-like cleavage at a pentabasic site in the TGN, a step required for PC2 to efficiently inactivate the CT peptide, while phosphorylation at Ser115 by Golgi kinases blocks proPC2 binding and inactivates the activating function [#7, #18, #20]. 7B2 is absolutely required for PC2 activation in vivo, with 7B2-null mice showing no PC2 activity, defective islet hormone processing, and lethal Cushing's syndrome from intermediate-lobe ACTH hypersecretion [#13, #19]. Beyond PC2, 7B2 acts as a broader secretory anti-aggregation chaperone, suppressing fibrillation of A\\u03b2, \\u03b1-synuclein, and IAPP and protecting neuronal cells from their cytotoxicity [#22, #23].\",\n  \"teleology\": [\n    {\n      \"year\": 1986,\n      \"claim\": \"Established that 7B2 resides in neuroendocrine secretory granules and is released by regulated exocytosis, defining its subcellular setting before any enzymatic role was known.\",\n      \"evidence\": \"Immuno-EM of pituitary cells and stimulated catecholamine co-release from bovine chromaffin cells\",\n      \"pmids\": [\"3681297\", \"3115588\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular function assigned at this stage\", \"Granule targeting determinants not defined\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Identified 7B2 as a precursor processed at its C-terminus, with only the processed form secreted in a regulated manner, framing the precursor/product distinction central to its later dual functions.\",\n      \"evidence\": \"Pulse-chase immunoprecipitation and peptide mapping in Xenopus neurointermediate lobe\",\n      \"pmids\": [\"2394742\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of processing unknown\", \"Processing enzyme not identified\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Resolved 7B2's core dual identity: it specifically and transiently binds the proPC2 precursor as a chaperone while its intact form potently and selectively inhibits PC2 but not PC1/PC3.\",\n      \"evidence\": \"Co-IP and pulse-chase in pituitary/Xenopus cells plus in vitro inhibition assays with recombinant 7B2; furin-mediated TGN maturation of pro-7B2 also defined\",\n      \"pmids\": [\"7913882\", \"8016065\", \"8034690\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Domains responsible for each activity not yet mapped\", \"Mechanism terminating inhibition unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mapped the bifunctional architecture and kinetics: the C-terminal CT peptide (Ki ~57 nM, requiring a Lys171-Lys172 site) confers inhibition while the 21-kDa product facilitates proPC2 maturation, and proPC2 binding is Ca2+-dependent via the pro-7B2 pentabasic site.\",\n      \"evidence\": \"Stable transfection in multiple neuroendocrine lines, mutagenesis, fluorogenic inhibitor kinetics with purified PC2, calcium-chelation co-IP\",\n      \"pmids\": [\"7790360\", \"7722516\", \"7782286\", \"7727407\", \"7672117\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PPII/helix interaction not yet defined\", \"Order of folding vs binding unresolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Defined the N-terminal interaction surface and the inhibitory shutoff mechanism: a polyproline helix is required for proPC2 binding, and PC2 itself cleaves the CT peptide at an internal Lys-Lys site (with CPE trimming) to terminate inhibition.\",\n      \"evidence\": \"Proline point mutagenesis with four functional assays; in vitro CT peptide cleavage with purified PC2 plus CPE; thermal stabilization assays on purified PC2\",\n      \"pmids\": [\"8798569\", \"8643504\", \"8660652\", \"8681965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise sequence of dissociation vs maturation events partially unresolved\", \"Atomic structure of complex absent\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Clarified mechanism timing: proPC2 must fold before binding 7B2, after which 7B2 enables ER-to-Golgi transport and acidic-pH activation, reconstitutable in Golgi-enriched fractions.\",\n      \"evidence\": \"Pulse-chase, glycanase sensitivity, subcellular fractionation, and in vitro activation in Golgi fractions\",\n      \"pmids\": [\"9348280\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational nature of the activation-competent state not structurally defined\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified PC2 determinants of binding and proved in vivo necessity: PC2 proregion plus Tyr194 and Asp309 are required for 7B2 binding, and PC2-expressing cells lacking 7B2 contain only inactive proPC2 until rescued by 7B2.\",\n      \"evidence\": \"Domain-swap chimeras and point mutagenesis of PC2; stable 7B2 transfection rescue in PC2-expressing cells; hypoglycemic shock model\",\n      \"pmids\": [\"9422782\", \"9645470\", \"9881669\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether these residues form a contiguous binding epitope not structurally confirmed\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Genetic ablation established 7B2 as absolutely required for PC2 activation in vivo and revealed PC2-independent endocrine functions, including a lethal ACTH hypersecretion phenotype, and the minimal 36-residue activation unit was defined.\",\n      \"evidence\": \"7B2 null mouse with hormonal/histological phenotyping versus PC2 null; sequential deletion/mutagenesis mapping the 36-residue activation core; antisense suppression in rMTC cells\",\n      \"pmids\": [\"10089884\", \"10409712\", \"10198237\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of PC2-independent pituitary functions unresolved\", \"Secretory-granule sorting partner unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Refined the inhibitory and binding interfaces: CT peptide residues 3\\u201318 with a Lys-Lys pair and both main- and side-chain contacts drive inhibition, and PC2 residues 242\\u2013248 govern 7B2 binding and CT-peptide inhibition.\",\n      \"evidence\": \"Alanine scanning and stereo-isomer CT analogues; PC2 catalytic-domain mutagenesis with binding and processing readouts\",\n      \"pmids\": [\"10673395\", \"10799554\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of CT peptide bound to PC2 active site\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Connected pro-7B2 maturation to inhibition control: furin cleavage of the pentabasic site is needed to produce PC2 capable of efficiently inactivating the CT peptide, decoupling activation from inhibitor turnover.\",\n      \"evidence\": \"CT-peptide and furin-site mutants tested in cell-free activation and HEK293 transfection assays\",\n      \"pmids\": [\"11677272\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural reason furin cleavage gates CT inactivation unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mechanistically linked the 7B2-null lethality to a dopaminergic deficiency: reduced pituitary dopamine drives ACTH/corticosterone excess, and adrenalectomy rescues survival.\",\n      \"evidence\": \"Adrenalectomy rescue of 7B2 null mice with ACTH, corticosterone, and dopamine measurements\",\n      \"pmids\": [\"11854475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How 7B2 loss lowers pituitary dopamine mechanistically not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Revealed phospho-regulation: Golgi-kinase phosphorylation at Ser115 abolishes proPC2 binding and activation, providing a post-translational off-switch for the chaperone function.\",\n      \"evidence\": \"32P labeling, phosphoamino acid analysis, Ser115 mutagenesis, co-IP, and cell-free activation assays\",\n      \"pmids\": [\"16286464\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the responsible Golgi kinase not pinned down\", \"Physiological trigger for phosphorylation unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrated 7B2 acts as an anti-aggregation chaperone toward proPC2 itself, solubilizing oligomers and maintaining an activation-competent conformation.\",\n      \"evidence\": \"Cross-linking, sucrose gradients, velocity sedimentation, and exogenous recombinant 7B2 addition to proPC2-expressing cells\",\n      \"pmids\": [\"18467442\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether anti-aggregation and activation are separable activities unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed 7B2 modulates PC2-mediated processing in a cell-type-specific manner, notably boosting glucagon production in alpha cells by routing PC2 to secretory granules.\",\n      \"evidence\": \"Adenoviral overexpression and siRNA knockdown across alpha, beta, and pituitary cells with in vivo glucagon corroboration\",\n      \"pmids\": [\"22013069\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Basis of cell-type specificity not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Broadened 7B2's chaperone role beyond PC2 to general amyloid suppression, blocking A\\u03b2 and \\u03b1-synuclein fibrillation and cytotoxicity and co-localizing with disease deposits.\",\n      \"evidence\": \"In vitro ThT fibrillation assays, gain/loss-of-function in Neuro-2A cells, and immunofluorescence in mouse and human brain\",\n      \"pmids\": [\"23172224\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of anti-amyloid activity unestablished\", \"Region mediating broad chaperone activity not mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extended the anti-aggregation activity to IAPP and tied reduced 7B2\\u2022PC2 activity to X-linked hypophosphatemia pathogenesis, with pharmacological rescue in the hyp-mouse.\",\n      \"evidence\": \"In vitro hIAPP fibrillation and cell-protection assays with deletion mapping; osteoblast gain/loss-of-function and Hexa-D-Arginine rescue in hyp-mice\",\n      \"pmids\": [\"24042052\", \"22886699\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether anti-aggregation contributes to bone phenotype unclear\", \"Generality of disease relevance not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The atomic structure of the 7B2\\u2013proPC2 complex and the molecular basis of 7B2's PC2-independent and broad anti-amyloid functions remain to be resolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal/cryo-EM structure of the chaperone or inhibitory complex\", \"PC2-independent endocrine roles mechanistically undefined\", \"Physiological role of broad anti-aggregation activity in vivo unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 4, 5, 16, 30]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 5, 8, 30]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 21, 22, 23]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [21, 22, 23]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 3, 9]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [7, 9, 20]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [33, 8, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2, 9, 13]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [9, 24, 29]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PCSK2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}