{"gene":"STIP1","run_date":"2026-06-10T07:46:43","timeline":{"discoveries":[{"year":1989,"finding":"STI1 (yeast ortholog of STIP1) was identified as a stress-inducible gene encoding a ~66 kDa protein; disruption caused impaired growth at high and low temperatures, and overexpression trans-activated the SSA4 (HSP70) promoter, indicating a role in mediating the heat shock response.","method":"Gene disruption, overexpression with reporter gene fusion, two-dimensional gel electrophoresis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO phenotype and reporter assay, single lab, multiple orthogonal methods","pmids":["2674681"],"is_preprint":false},{"year":1997,"finding":"Yeast Sti1 acts as a general co-chaperone at an intermediate step in the Hsp90-dependent maturation of client proteins (glucocorticoid receptor, v-Src); deletion of STI1 reduces GR and v-Src activity in vivo and increases GR-Ydj1 complexes, placing Sti1 downstream of Hsp70 (Ydj1) and upstream of mature Hsp90-client complexes.","method":"Genetic epistasis (sti1Δ combined with hsp90ts mutations, GR/v-Src activity assays), co-immunoprecipitation of client complexes in yeast","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic interactions, multiple client proteins tested, epistasis with Hsp70 and Hsp90 mutants, replicated across clients","pmids":["8972212"],"is_preprint":false},{"year":2000,"finding":"Human STIP1 (StIP1) preferentially associates with unphosphorylated (inactive) Stat3 and also binds members of the Janus kinase (JAK) family; overexpression of the Stat3-binding domain of STIP1 blocks Stat3 activation, nuclear translocation, and Stat3-dependent transcription, suggesting STIP1 acts as a scaffold promoting JAK–Stat3 interaction.","method":"Co-immunoprecipitation, overexpression dominant-negative domain, reporter gene assay, nuclear translocation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and functional reporter, single lab","pmids":["10954736"],"is_preprint":false},{"year":2003,"finding":"Sti1 is a non-competitive inhibitor of the Hsp90 ATPase; it binds both the N- and C-terminal domains of Hsp90 and prevents the N-terminal dimerization reaction required for efficient ATP hydrolysis, with the first 24 amino acids of Hsp90 being important for this interaction.","method":"In vitro ATPase assay, binding analysis with truncated Hsp90 constructs, kinetic inhibition analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro ATPase inhibition, defined binding domains, mechanism confirmed","pmids":["12525481"],"is_preprint":false},{"year":2005,"finding":"Sti1p regulates Hsp70 and Hsp90 independently via distinct TPR domains: TPR1 mutations impair Hsp70 regulation (without affecting Hsp90), while TPR2A/TPR2B mutations impair Hsp90 regulation (without affecting Hsp70); Hsp90 is implicated as a TPR2B ligand; client folding requires Sti1p to bridge both chaperones simultaneously.","method":"Site-directed mutagenesis of TPR domains, yeast [PSI+] prion assay for Hsp70 activity, Hsp90-inhibitor assay for Hsp90 activity, client folding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal genetic/functional assays, domain-specific mutations, two chaperone systems tested independently","pmids":["16100115"],"is_preprint":false},{"year":2005,"finding":"STIP1/STI1 interacts with cellular prion protein (PrPC) via immunoprecipitation; the OR and N-terminal hydrophobic region of PrPC are required for PrPC-STI1-mediated activation of superoxide dismutase (SOD) activity and cell survival signaling.","method":"Co-immunoprecipitation, inhibitory peptide competition assays, SOD activity assay in PrP-null and PrP-expressing neuronal cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and functional assay with inhibitory peptides, single lab","pmids":["15670743"],"is_preprint":false},{"year":2005,"finding":"In yeast, mutations in Sti1 DP2 domain completely disrupt Sti1 function in vivo, while TPR1 and TPR2B have redundant roles in Hsp70 binding; a single amino acid alteration in TPR2A disrupts Hsp90 interaction but does not significantly affect function alone.","method":"Site-directed mutagenesis, genetic screen, co-immunoprecipitation in yeast","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-directed mutagenesis combined with genetic screen and Co-IP, single lab","pmids":["16219779"],"is_preprint":false},{"year":2006,"finding":"Wild-type Hsp90 binds Sti1 in a nucleotide-independent manner in yeast cell extracts, while Sba1 and Cpr6 interact with Hsp90 specifically in the presence of the non-hydrolyzable ATP analog AMP-PNP; Hsp90 mutations altering ATP binding reduce Sti1 interaction in the presence of nucleotide.","method":"Co-immunoprecipitation from yeast extracts with wild-type and mutant Hsp90 forms, AMP-PNP competition","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean Co-IP with multiple Hsp90 mutants, single lab","pmids":["17101799"],"is_preprint":false},{"year":2007,"finding":"Both TPR1 and TPR2B of Sti1 contribute redundantly to Hsp70 binding in vivo; TPR2A is required for Hsp90 interaction but requires TPR2B for full Hsp90 binding in isolation; TPR2A is sufficient for Sti1 dimerization; the DP2 domain is essential for in vivo function but dispensable for Hsp70/Hsp90 interaction or dimerization; Sti1 mutants with reduced Hsp70 interaction show reduced recovery of Hsp70 in Hsp90 complexes.","method":"Truncation mutagenesis, in vivo co-immunoprecipitation, in vitro binding assays with purified proteins","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution combined with in vivo Co-IP and multiple truncation mutants, single lab","pmids":["17300223"],"is_preprint":false},{"year":2007,"finding":"Extracellular/secreted STI1 induces proliferation of human glioblastoma cells (A172) via MAPK (ERK) and PI3K signaling pathways, and this effect involves cellular prion protein (PrPC).","method":"Thymidine incorporation assay, pathway inhibitor experiments, extracellular STI1 application","journal":"Glia","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pharmacological inhibitors only, no direct binding assay reported","pmids":["17886292"],"is_preprint":false},{"year":2009,"finding":"Interaction of PrPC with hop/STI1 induces loss of PrP helical structures (perturbation of PrP helix 143–153) and a C-terminal compaction of hop/STI1, as revealed by CD, fluorescence spectroscopy, and SAXS; free murine hop/STI1 is monomeric by both SAXS and size-exclusion chromatography.","method":"Circular dichroism (CD), fluorescence spectroscopy, small angle X-ray scattering (SAXS), size-exclusion chromatography","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple biophysical methods (CD, SAXS) on recombinant proteins, single lab","pmids":["19703931"],"is_preprint":false},{"year":2010,"finding":"Deletion of STI1 in yeast both suppresses Ssa1-21 (Hsp70 mutant)-mediated impairment of [PSI+] and blocks Hsp104-mediated curing of [PSI+] prions; Sti1 variants defective in Hsp70 or Hsp90 interaction cure less efficiently, and Hsp90 inhibitor abolishes curing, demonstrating Sti1 acts in prion curing through both Hsp70 and Hsp90 interactions.","method":"Genetic epistasis, STI1 deletion, domain-specific mutations, Hsp90 inhibitor treatment, prion-curing assays in yeast","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic epistasis experiments with Hsp70, Hsp90, and Sti1 mutants, replicated across conditions","pmids":["20479121"],"is_preprint":false},{"year":2012,"finding":"Sti1/Hop has a modular architecture: TPR2A is the high-affinity Hsp90-binding site; TPR1 and TPR2B bind Hsp70 with moderate affinity; DP1 and DP2 have homologous α-helical folds (determined by NMR); the TPR2A–TPR2B segment is the core Hsp90 inhibitory module; TPR2A and TPR2B are connected by a rigid linker orienting their binding sites in opposite directions, allowing simultaneous binding of TPR2A to Hsp90 C-terminal domain and TPR2B to Hsp70; DP2 is important for client activation in vivo.","method":"NMR structure determination of DP domains, crystal structure of TPR2A–TPR2B segment, in vitro binding assays, in vivo client activation assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure, NMR, and functional validation in one study, multiple orthogonal methods","pmids":["22227520"],"is_preprint":false},{"year":2012,"finding":"Sti1 stabilizes multiple regions in all three domains of Hsp90 and slows dimer dissociation; it inhibits Hsp90 ATPase by preventing N-terminal dimerization and docking of the N-terminal with the middle domain; crosslinking-MS identified Sti1 segments in close proximity to the Hsp90 N-terminal domain; the linker length between Hsp90 C-terminal dimerization domain and MEEVD motif is important for Sti1 association rates.","method":"Hydrogen exchange mass spectrometry (HX-MS), crosslinking mass spectrometry, mutant Hsp90 analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — HX-MS and crosslinking-MS provide conformational dynamics data, two orthogonal biophysical methods, single lab","pmids":["22354036"],"is_preprint":false},{"year":2013,"finding":"Sti1 modulates spatial quality control of amyloid-like proteins (Htt103Q, Rnq1) in yeast cytosol: loss of Sti1 exacerbates Htt toxicity and hinders foci formation; elevation of Sti1 suppresses toxicity and organizes small Htt103Q foci into larger perinuclear assemblies containing thioflavin-T-positive amyloid-like material.","method":"High-copy suppressor screen in yeast, fluorescence microscopy, thioflavin-T staining, toxicity assays","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic screen plus multiple functional readouts and imaging, single lab","pmids":["24109600"],"is_preprint":false},{"year":2014,"finding":"Sti1/Hop is a dynamic elongated protein with a flexible N-terminal module and rigid C-terminal module; without Hsp90, Sti1 is more compact and TPR2B is the high-affinity Hsp70-binding site; in the presence of Hsp90, Hsp70 shifts its preference away from TPR2B; the linker connecting the two modules is crucial for Hsp70 interaction and client activation in vivo.","method":"Single-molecule fluorescence (FRET), NMR, truncation mutants, in vivo client activation assays, fluorescence cross-correlation spectroscopy","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — single-molecule FRET plus NMR plus functional assays, multiple orthogonal methods","pmids":["25851214"],"is_preprint":false},{"year":2014,"finding":"Cytoplasmic STI1 directly interacts with the small GTPase Rnd1; this interaction is specific for Rnd1 (not other Rnd family members); STI1 overexpression prevents Rnd1-plexin-A1-mediated cytoskeleton retraction in COS collapse assay and enhances neurite outgrowth in PC-12 cells.","method":"Co-immunoprecipitation, COS cell collapse assay, PC-12 neurite outgrowth assay, specificity tests with Rnd family members","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus two functional assays with specificity controls, single lab","pmids":["24690281"],"is_preprint":false},{"year":2014,"finding":"Yeast Sti1 is phosphorylated at inhibitory sites; human Hop is also subject to inhibitory phosphorylation; phospho-mimetic variants of Hop have reduced ability to activate clients in vivo, reduced affinity for Hsp70, and reduced interaction with Hsp90 (for human Hop), inducing structural rearrangements in the protein core.","method":"Phospho-mimetic mutagenesis, in vivo client activation assays, affinity binding assays, structural analysis","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phospho-mimetic mutations plus functional and binding assays, both yeast and human proteins tested, single lab","pmids":["25504578"],"is_preprint":false},{"year":2016,"finding":"STIP1 co-immunoprecipitates with actin from HEK293T cells and directly interacts with actin in vitro via its C-terminal TPR2AB-DP2 domain; STIP1 can stimulate actin ATPase activity in vitro; STIP1 depletion leads to increased nuclear actin accumulation, F-actin disorganization, and altered cofilin/profilin levels.","method":"Co-immunoprecipitation from HEK293T cells, in vitro direct binding/ATPase assay, STIP1 knockdown with fluorescence imaging of actin structures, western blot for cofilin and profilin","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro binding and ATPase assay plus cellular imaging and Co-IP, single lab","pmids":["32365744"],"is_preprint":false},{"year":2016,"finding":"STIP1 interacts with the Axin scaffold protein, enhances the Axin–DVL2 interaction, and thereby activates β-catenin/TCF (Wnt) signaling in hepatocellular carcinoma cells.","method":"Co-immunoprecipitation, STIP1 knockdown/overexpression with downstream Wnt reporter","journal":"Gene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP and KD/OE functional assay, single lab","pmids":["29596884"],"is_preprint":false},{"year":2016,"finding":"STIP1 domains DP1, TPR1, and TPR2A all contribute to PrPC binding: DP1 binds the N-terminal region of PrP (residues 23–95), TPR1 and TPR2A bind the C-terminal region (residues 90–231); only TPR1 and TPR2A directly inhibit AβO binding to PrPC and AβO-induced neuronal cell death; the TPR2A–PrP interface is extensive and partially overlaps with the Hsp90-binding site, suggesting a PrP–STIP1–Hsp90 ternary complex.","method":"NMR chemical shift mapping, binding domain mapping with truncated STIP1 constructs, cell death assays, amyloid-beta oligomer competition binding assays","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — NMR structural mapping plus functional cell death assays, single lab","pmids":["27208175"],"is_preprint":false},{"year":2016,"finding":"Deletion of STI1 in yeast causes alterations in mitochondrial morphology and lower steady-state levels of a subset of mitochondrial proteins; double deletion of STI1 with mitochondrial import factors MIM1 or TOM20 shows synthetic growth phenotype; recombinant cytosolic domains of Tom20 and Tom70 bind Sti1 in vitro, suggesting Sti1 plays a direct or indirect role in mitochondrial protein import.","method":"Site-directed photo-crosslinking in yeast, genetic epistasis (double deletion growth assays), in vitro binding assay with Tom receptor domains, mitochondrial morphology imaging","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — photo-crosslinking, genetic epistasis, and in vitro binding assays, single lab","pmids":["27412066"],"is_preprint":false},{"year":2017,"finding":"Three S100A1 dimers associate with one STIP1 molecule in a calcium-dependent manner; each STIP1 TPR domain (TPR1, TPR2A, TPR2B) binds one S100A1 dimer with different affinities (TPR2B highest); S100A1 binds each TPR domain through a common interface (α-helices III and IV) accessible only after calcium-induced conformational change; TPR2B binding involves insertion of S100A1 into its hydrophobic cleft.","method":"Isothermal titration calorimetry (ITC), domain-specific binding assays with isolated TPR domains, calcium-dependence studies","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — ITC quantitative binding with multiple domain constructs, stoichiometry defined, single lab with rigorous controls","pmids":["28408431"],"is_preprint":false},{"year":2018,"finding":"Hop/STIP1 depletion or overexpression reduces emerin protein levels via proteasomal and lysosomal pathways; Hop and emerin co-immunoprecipitate in a complex that also contains Hsp70 but not Hsp90; TPR2AB domain of Hop is required for the Hop-emerin association; loss of Hop or emerin causes nuclear deformation and decreased nuclear size; nuclear defects from Hop loss are rescued by emerin overexpression.","method":"Co-immunoprecipitation, STIP1 depletion/overexpression, proteasome/lysosome inhibitor experiments, nuclear morphology imaging, rescue experiment","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus domain mapping and phenotypic rescue, single lab","pmids":["30449594"],"is_preprint":false},{"year":2020,"finding":"Human cell lines and budding yeast with deletion of STIP1/STI1 display reduced proteasome activity due to inefficient capping of the 20S core particle with regulatory particles; unexpectedly, knockout cells are more proficient at preventing protein aggregation and promoting protein refolding, because a more efficient prokaryote-like Hsp70–Hsp90 binary complex (without Hop restraint) compensates; this was also demonstrated in vitro.","method":"Gene knockout in human cells and yeast, in vitro reconstitution of Hsp70–Hsp90 chaperone activity, proteasome activity assays, protein aggregation/refolding assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution plus KO in two organisms, multiple orthogonal assays, significant mechanistic insight","pmids":["33239621"],"is_preprint":false},{"year":2021,"finding":"STI1 co-immunoprecipitates α-synuclein; NMR analyses show direct interaction of α-synuclein with the TPR2A domain (but not TPR1 or TPR2B) of STI1, involving the C-terminal domain of α-synuclein; the STI1 TPR2A domain facilitates S129 phosphorylation of α-synuclein by Polo-like kinase 3 in vitro; mice over-expressing STI1 and Hsp90β show elevated S129 α-synuclein phosphorylation and inclusion formation; reduced STI1 function decreases inclusion formation and phosphorylation while mitigating motor and cognitive deficits.","method":"Co-immunoprecipitation, NMR interaction mapping, in vitro phosphorylation assay with PLK3, mouse model with altered STI1 expression","journal":"Acta neuropathologica","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — NMR direct interaction mapping plus in vitro kinase assay plus in vivo mouse models, multiple orthogonal methods","pmids":["36121476"],"is_preprint":false},{"year":2021,"finding":"Hsp90 and its co-chaperone Sti1 modulate TDP-43 misfolding, inclusion formation, aggregation, and cellular toxicity; Sti1 specifically interacts with TDP-43 and strongly modulates TDP-43 toxicity in a dose-dependent manner in yeast and mammalian neuronal cells.","method":"Co-immunoprecipitation, TDP-43 aggregation assay, toxicity assays in yeast and mammalian neuronal cells, genetic manipulations of STI1/Hsp90","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional toxicity and aggregation assays in two systems, single lab","pmids":["33908654"],"is_preprint":false},{"year":2021,"finding":"STIP1 can be isolated in a complex with actin and Hsp90 from HEK293T cells; STIP1 directly interacts with actin via the C-terminal TPR2AB-DP2 domain in vitro; STIP1 can stimulate the in vitro ATPase activity of actin.","method":"Co-immunoprecipitation, in vitro direct binding assay, in vitro ATPase stimulation assay","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro assay plus Co-IP, single lab","pmids":["32365744"],"is_preprint":false},{"year":2022,"finding":"JAK2 phosphorylates STIP1 at tyrosine residues Y134 and Y152, promoting STIP1 protein stability, inducing nuclear-cytoplasmic shuttling, and promoting STIP1 secretion into the extracellular space; JAK2-mediated STIP1 phosphorylation enhances cell viability and increases resistance to cisplatin-induced cell death; disrupting STIP1–JAK2 interaction decreases JAK2 protein levels.","method":"Site-directed mutagenesis of phosphorylation sites, cell-penetrating inhibitory peptides, immunoblotting for stability, nuclear-cytoplasmic fractionation, ELISA for secretion, cell viability assays","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-directed mutagenesis plus functional assays (viability, localization, secretion), single lab","pmids":["35269562"],"is_preprint":false},{"year":2023,"finding":"STIP1 binds to HSP40, HSP70, and HSP90 in rat H9c2 cardiomyocytes; overexpression of STIP1 promotes the transition of Cx43 from Cx43-HSP70 to Cx43-HSP90 complexes and inhibits Cx43 ubiquitination; knockdown of STIP1 has the opposite effect; HSP90 inhibition counteracts the inhibitory effect of STIP1 overexpression on Cx43 ubiquitination.","method":"Co-immunoprecipitation, STIP1 overexpression/knockdown, HSP90 inhibitor treatment, ubiquitination assays in H9c2 cardiomyocytes","journal":"Cytotechnology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional ubiquitination assay with gain/loss-of-function and HSP90 inhibitor, single lab","pmids":["37187948"],"is_preprint":false},{"year":2023,"finding":"The lncRNA LINC01226 binds STIP1 protein, leads to disassembly of the STIP1–HSP90 complex, elevates HSP90–β-catenin interactions, stabilizes β-catenin protein, and activates Wnt/β-catenin signaling to promote gastric cancer progression.","method":"RNA-protein pulldown, co-immunoprecipitation, LINC01226 overexpression/knockdown with downstream β-catenin/TCF assays","journal":"Cancer letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — RNA-protein interaction and Co-IP, but mechanistic evidence for complex disassembly is indirect, single lab","pmids":["37806517"],"is_preprint":false},{"year":2024,"finding":"During proteostatic stress, Sti1 forms cytoplasmic inclusions in yeast and mammalian cells that overlap with misfolded proteins; deletion of STI1 causes accumulation of soluble misfolded ubiquitinated proteins and activates the heat shock response; Sti1 sequesters misfolded proteins during stress independently of its Hsp90 ATPase regulatory function.","method":"Fluorescence imaging of inclusions in yeast and mammalian cells, soluble/insoluble protein fractionation, ubiquitin accumulation assay, heat shock reporter assay, STI1 deletion","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cellular imaging plus biochemical fractionation and reporter assay, two organisms tested, single lab","pmids":["39739753"],"is_preprint":false},{"year":2025,"finding":"The mitochondrial targeting signal (MTS) directly engages the co-chaperones of Hsc70 including Stip1/HOP via site-specific photo-crosslinking; STIP1/Hop and St13 facilitate chaperone retention on the mature domain of mitochondrial precursor proteins; during acute import stress, this Hsp90 co-chaperone interaction (requiring the MTS) buffers precursor degradation and maintains import competence.","method":"Site-specific photo-crosslinking in cells, biochemical reconstitution, import stress experiments","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — photo-crosslinking and biochemical reconstitution in single preprint study","pmids":["bio_10.1101_2025.01.18.633710"],"is_preprint":true},{"year":2025,"finding":"STIP1/HOP directly interacts with α-synuclein via two binding motifs in the C-terminus of α-synuclein that dynamically compete for the TPR2A domain of STIP1; STIP1 binding attenuates α-synuclein fibril formation while promoting accumulation of high-molecular-weight amorphous and A11-positive oligomeric species that are more cytotoxic to neuronal cells.","method":"NMR interaction mapping, in vitro aggregation assays, A11 oligomer dot-blot, neuronal cell viability assays","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — NMR mapping plus in vitro aggregation and cytotoxicity assays, single preprint","pmids":["bio_10.1101_2025.03.26.645247"],"is_preprint":true},{"year":2025,"finding":"STIP1 interacts with adenosylhomocysteinase (AHCY/SAHH) and changes AHCY conformation; STIP1 facilitates AHCY binding to lactate dehydrogenase A (LDHA), stimulating glycolysis; AHCY then recruits PRMT3 to methylate LDHA at R106, inhibiting ubiquitination-mediated AHCY degradation; STIP1 knockout in mice inhibits 4NQO-induced esophageal tumorigenesis.","method":"Co-immunoprecipitation, conformational assay, in vivo mouse knockout, glycolysis assays, methylation assays","journal":"Exploration (Beijing, China)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — Co-IP plus in vivo KO, but pathway mechanism is complex and reported in a single study with limited mechanistic reconstitution","pmids":["41163796"],"is_preprint":false}],"current_model":"STIP1/Hop/Sti1 is a modular co-chaperone that simultaneously bridges Hsp70 (via TPR1 and TPR2B) and Hsp90 (via TPR2A) to facilitate client protein transfer between these chaperones; it non-competitively inhibits the Hsp90 ATPase by blocking N-terminal Hsp90 dimerization; its activity is negatively regulated by phosphorylation at species-specific inhibitory sites; beyond its canonical chaperone scaffolding role, STIP1 can independently sequester misfolded proteins during acute stress, regulates proteasome assembly, directly interacts with cellular prion protein (PrPC) to modulate neuronal signaling and neuroprotection, directly binds α-synuclein via its TPR2A domain to promote formation of cytotoxic oligomers, interacts with actin to regulate cytoskeletal dynamics, and can act as a scaffold for signaling complexes including JAK/STAT3 pathways."},"narrative":{"mechanistic_narrative":"STIP1 (Hop/Sti1) is a modular co-chaperone adaptor that physically bridges the Hsp70 and Hsp90 chaperone machines to coordinate the maturation of client proteins, a role first established genetically in yeast where Sti1 acts at an intermediate step downstream of Hsp70 (Ydj1) and upstream of mature Hsp90-client complexes [PMID:8972212]. It engages the two chaperones through distinct tetratricopeptide repeat (TPR) domains: TPR2A is the high-affinity Hsp90-binding site while TPR1 and TPR2B bind Hsp70, and client folding requires Sti1 to bridge both chaperones simultaneously [PMID:16100115, PMID:22227520]. Structurally, Sti1/Hop is an elongated, conformationally dynamic protein in which a rigid TPR2A–TPR2B linker orients the two binding sites in opposite directions to permit concurrent Hsp70 and Hsp90 engagement, with Hsp90 binding shifting Hsp70 away from TPR2B [PMID:22227520, PMID:25851214]. Functionally, STIP1 acts as a non-competitive inhibitor of the Hsp90 ATPase, binding both N- and C-terminal regions of Hsp90, stabilizing its domains, and preventing the N-terminal dimerization and N–middle domain docking required for ATP hydrolysis [PMID:12525481, PMID:22354036]; this restraining activity is itself negatively regulated by inhibitory phosphorylation that reduces chaperone affinity and client activation [PMID:25504578]. By restraining Hsp70–Hsp90 complex formation, STIP1 also governs downstream proteostasis outcomes — its loss reduces 20S proteasome capping and proteasome activity yet paradoxically improves aggregation prevention and refolding via a more efficient Hsp70–Hsp90 binary complex [PMID:33239621] — and during proteostatic stress STIP1 independently sequesters misfolded ubiquitinated proteins into cytoplasmic inclusions in a manner separable from its Hsp90 ATPase regulatory function [PMID:39739753]. Beyond canonical chaperoning, STIP1 directly binds cellular prion protein (PrPC) through DP1, TPR1, and TPR2A to support neuroprotective signaling and to block amyloid-β oligomer binding [PMID:15670743, PMID:27208175], and it directly engages α-synuclein via its TPR2A domain, facilitating PLK3-mediated S129 phosphorylation and promoting cytotoxic oligomeric species in vivo [PMID:36121476]. STIP1 additionally functions as a scaffold in JAK–STAT3 signaling [PMID:10954736], binds actin and stimulates its ATPase to regulate cytoskeletal organization [PMID:32365744], and contributes to mitochondrial precursor import [PMID:27412066].","teleology":[{"year":1989,"claim":"Established STIP1's founding identity as a stress-inducible factor before any chaperone role was known, linking it to the heat shock response.","evidence":"Gene disruption and overexpression with HSP70 promoter reporter in yeast","pmids":["2674681"],"confidence":"Medium","gaps":["No molecular mechanism for HSP70 promoter trans-activation defined","Direct chaperone partners not yet identified"]},{"year":1997,"claim":"Placed Sti1 mechanistically within the Hsp70-to-Hsp90 client maturation pathway, defining it as an intermediate co-chaperone rather than an independent factor.","evidence":"Genetic epistasis with hsp90ts mutants and client (GR, v-Src) activity/Co-IP assays in yeast","pmids":["8972212"],"confidence":"High","gaps":["Domain basis for dual chaperone engagement not yet resolved","Biochemical effect on Hsp90 enzymatic activity unknown"]},{"year":2000,"claim":"Identified a chaperone-independent scaffolding role linking STIP1 to JAK–STAT3 signaling, broadening its functional scope.","evidence":"Co-IP, dominant-negative domain overexpression, and STAT3 reporter/translocation assays","pmids":["10954736"],"confidence":"Medium","gaps":["Whether scaffolding requires chaperone activity not addressed","Single lab, no structural mapping of the STAT3-binding region"]},{"year":2003,"claim":"Defined the biochemical mechanism of Hsp90 regulation, showing STIP1 non-competitively inhibits the ATPase by blocking N-terminal dimerization.","evidence":"Reconstituted in vitro ATPase assays and binding to truncated Hsp90 constructs","pmids":["12525481"],"confidence":"High","gaps":["High-resolution structure of the inhibitory module not yet available","Coupling to client transfer not directly shown"]},{"year":2005,"claim":"Assigned division of labor among Sti1 TPR domains, showing TPR1 governs Hsp70 and TPR2A/TPR2B govern Hsp90 regulation independently.","evidence":"Domain-specific mutagenesis with [PSI+] prion and Hsp90-inhibitor functional assays in yeast","pmids":["16100115","16219779"],"confidence":"High","gaps":["DP2 essential function mechanistically unexplained","Redundancy vs specialization of TPR1/TPR2B not fully resolved"]},{"year":2005,"claim":"Extended STIP1 function to extracellular neuronal signaling by demonstrating direct PrPC interaction driving neuroprotection.","evidence":"Co-IP, inhibitory peptide competition, and SOD/cell survival assays in neuronal cells","pmids":["15670743"],"confidence":"Medium","gaps":["Binding interface not mapped at residue level","Downstream signaling cascade incompletely defined"]},{"year":2007,"claim":"Refined the domain model, showing TPR1/TPR2B redundancy for Hsp70 and that TPR2A drives both Hsp90 binding and Sti1 dimerization while DP2 is dispensable for interactions but essential in vivo.","evidence":"Truncation mutagenesis with in vivo Co-IP and in vitro binding; nucleotide-dependence Co-IP with Hsp90 mutants","pmids":["17300223","17101799"],"confidence":"High","gaps":["In vivo essential role of DP2 still mechanistically unexplained","Conformational coupling between domains not yet visualized"]},{"year":2010,"claim":"Demonstrated that Sti1 acts in prion propagation/curing through both its Hsp70 and Hsp90 interactions, integrating its dual-chaperone role into amyloid handling.","evidence":"Genetic epistasis, domain mutants, and Hsp90 inhibitor in yeast [PSI+] curing assays","pmids":["20479121"],"confidence":"High","gaps":["Direct action on prion substrate vs chaperone modulation not separated","Relevance to mammalian amyloids not tested here"]},{"year":2012,"claim":"Provided the structural basis for simultaneous dual-chaperone bridging and the core Hsp90 inhibitory module, unifying earlier domain genetics.","evidence":"Crystal structure of TPR2A–TPR2B, NMR of DP domains, binding and client activation assays; HX-MS and crosslinking-MS of the Hsp90 complex","pmids":["22227520","22354036"],"confidence":"High","gaps":["Full-length Hop–Hsp70–Hsp90 ternary structure not solved","Dynamics of client handoff not captured"]},{"year":2014,"claim":"Revealed STIP1 as a conformationally dynamic adaptor whose Hsp70 preference is allosterically reset by Hsp90 binding, and expanded its roles to spatial protein quality control, cytoskeletal regulation, and inhibitory phosphorylation.","evidence":"Single-molecule FRET and NMR; yeast Htt/Rnq1 suppressor and imaging assays; Rnd1 Co-IP with collapse/neurite assays; phospho-mimetic mutagenesis","pmids":["25851214","24109600","24690281","25504578"],"confidence":"High","gaps":["Physiological kinases for inhibitory sites not identified here","Mechanistic link between adaptor dynamics and quality-control function unclear"]},{"year":2016,"claim":"Mapped the PrPC-binding architecture and showed STIP1 blocks amyloid-β oligomer toxicity, while uncovering additional partners in cytoskeleton, nuclear envelope, mitochondrial import, and Wnt signaling.","evidence":"NMR chemical-shift mapping with PrP/AβO assays; actin Co-IP/ATPase and imaging; emerin Co-IP, domain mapping and rescue; Tom20/Tom70 binding and yeast genetics; Axin Co-IP/Wnt reporter","pmids":["27208175","32365744","30449594","27412066","29596884"],"confidence":"Medium","gaps":["Whether non-chaperone partners require Hsp70/Hsp90 engagement not resolved","Several interactions rest on single-lab Co-IP without reciprocal structural validation"]},{"year":2017,"claim":"Quantified calcium-dependent S100A1 engagement of all three TPR domains, defining STIP1 as a calcium-responsive multivalent TPR hub.","evidence":"Isothermal titration calorimetry with isolated TPR domains and calcium-dependence studies","pmids":["28408431"],"confidence":"High","gaps":["Functional consequence of S100A1 binding for chaperone cycle untested","Cellular context of the interaction undefined"]},{"year":2020,"claim":"Resolved how loss of STIP1 reshapes proteostasis, showing it is required for proteasome capping yet restrains an intrinsically efficient Hsp70–Hsp90 binary complex.","evidence":"Knockout in human cells and yeast plus in vitro reconstitution of chaperone activity and proteasome/refolding assays","pmids":["33239621"],"confidence":"High","gaps":["Mechanism of proteasome capping defect not detailed","When the binary complex is advantageous in vivo unclear"]},{"year":2021,"claim":"Established direct, TPR2A-specific engagement of disease-associated aggregating proteins, mechanistically linking STIP1 to synucleinopathy and TDP-43 proteinopathy.","evidence":"Co-IP, NMR mapping, in vitro PLK3 kinase assay and STI1-altered mouse models for α-synuclein; Co-IP and aggregation/toxicity assays for TDP-43","pmids":["36121476","33908654"],"confidence":"High","gaps":["Whether STIP1 promotes or detoxifies aggregates context-dependent and not fully reconciled","TDP-43 binding interface not mapped"]},{"year":2023,"claim":"Linked STIP1-directed Hsp70-to-Hsp90 client handoff to substrate stabilization in disease-relevant contexts and to oncogenic Wnt signaling.","evidence":"Co-IP, gain/loss-of-function and Hsp90 inhibitor with Cx43 ubiquitination in cardiomyocytes; lncRNA pulldown/Co-IP with β-catenin assays","pmids":["37187948","37806517"],"confidence":"Medium","gaps":["LINC01226-driven complex disassembly evidence is indirect","Generality across substrates not established"]},{"year":2025,"claim":"Sharpened the mechanistic picture of STIP1 in mitochondrial import buffering, α-synuclein oligomer toxicity, and a metabolic AHCY/LDHA axis driving tumorigenesis.","evidence":"Photo-crosslinking and reconstitution for MTS-driven import (preprint); NMR/aggregation/cytotoxicity for α-synuclein (preprint); 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stress-inducible gene encoding a ~66 kDa protein; disruption caused impaired growth at high and low temperatures, and overexpression trans-activated the SSA4 (HSP70) promoter, indicating a role in mediating the heat shock response.\",\n      \"method\": \"Gene disruption, overexpression with reporter gene fusion, two-dimensional gel electrophoresis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO phenotype and reporter assay, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"2674681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Yeast Sti1 acts as a general co-chaperone at an intermediate step in the Hsp90-dependent maturation of client proteins (glucocorticoid receptor, v-Src); deletion of STI1 reduces GR and v-Src activity in vivo and increases GR-Ydj1 complexes, placing Sti1 downstream of Hsp70 (Ydj1) and upstream of mature Hsp90-client complexes.\",\n      \"method\": \"Genetic epistasis (sti1Δ combined with hsp90ts mutations, GR/v-Src activity assays), co-immunoprecipitation of client complexes in yeast\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic interactions, multiple client proteins tested, epistasis with Hsp70 and Hsp90 mutants, replicated across clients\",\n      \"pmids\": [\"8972212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human STIP1 (StIP1) preferentially associates with unphosphorylated (inactive) Stat3 and also binds members of the Janus kinase (JAK) family; overexpression of the Stat3-binding domain of STIP1 blocks Stat3 activation, nuclear translocation, and Stat3-dependent transcription, suggesting STIP1 acts as a scaffold promoting JAK–Stat3 interaction.\",\n      \"method\": \"Co-immunoprecipitation, overexpression dominant-negative domain, reporter gene assay, nuclear translocation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and functional reporter, single lab\",\n      \"pmids\": [\"10954736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Sti1 is a non-competitive inhibitor of the Hsp90 ATPase; it binds both the N- and C-terminal domains of Hsp90 and prevents the N-terminal dimerization reaction required for efficient ATP hydrolysis, with the first 24 amino acids of Hsp90 being important for this interaction.\",\n      \"method\": \"In vitro ATPase assay, binding analysis with truncated Hsp90 constructs, kinetic inhibition analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro ATPase inhibition, defined binding domains, mechanism confirmed\",\n      \"pmids\": [\"12525481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Sti1p regulates Hsp70 and Hsp90 independently via distinct TPR domains: TPR1 mutations impair Hsp70 regulation (without affecting Hsp90), while TPR2A/TPR2B mutations impair Hsp90 regulation (without affecting Hsp70); Hsp90 is implicated as a TPR2B ligand; client folding requires Sti1p to bridge both chaperones simultaneously.\",\n      \"method\": \"Site-directed mutagenesis of TPR domains, yeast [PSI+] prion assay for Hsp70 activity, Hsp90-inhibitor assay for Hsp90 activity, client folding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal genetic/functional assays, domain-specific mutations, two chaperone systems tested independently\",\n      \"pmids\": [\"16100115\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"STIP1/STI1 interacts with cellular prion protein (PrPC) via immunoprecipitation; the OR and N-terminal hydrophobic region of PrPC are required for PrPC-STI1-mediated activation of superoxide dismutase (SOD) activity and cell survival signaling.\",\n      \"method\": \"Co-immunoprecipitation, inhibitory peptide competition assays, SOD activity assay in PrP-null and PrP-expressing neuronal cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and functional assay with inhibitory peptides, single lab\",\n      \"pmids\": [\"15670743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In yeast, mutations in Sti1 DP2 domain completely disrupt Sti1 function in vivo, while TPR1 and TPR2B have redundant roles in Hsp70 binding; a single amino acid alteration in TPR2A disrupts Hsp90 interaction but does not significantly affect function alone.\",\n      \"method\": \"Site-directed mutagenesis, genetic screen, co-immunoprecipitation in yeast\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-directed mutagenesis combined with genetic screen and Co-IP, single lab\",\n      \"pmids\": [\"16219779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Wild-type Hsp90 binds Sti1 in a nucleotide-independent manner in yeast cell extracts, while Sba1 and Cpr6 interact with Hsp90 specifically in the presence of the non-hydrolyzable ATP analog AMP-PNP; Hsp90 mutations altering ATP binding reduce Sti1 interaction in the presence of nucleotide.\",\n      \"method\": \"Co-immunoprecipitation from yeast extracts with wild-type and mutant Hsp90 forms, AMP-PNP competition\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean Co-IP with multiple Hsp90 mutants, single lab\",\n      \"pmids\": [\"17101799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Both TPR1 and TPR2B of Sti1 contribute redundantly to Hsp70 binding in vivo; TPR2A is required for Hsp90 interaction but requires TPR2B for full Hsp90 binding in isolation; TPR2A is sufficient for Sti1 dimerization; the DP2 domain is essential for in vivo function but dispensable for Hsp70/Hsp90 interaction or dimerization; Sti1 mutants with reduced Hsp70 interaction show reduced recovery of Hsp70 in Hsp90 complexes.\",\n      \"method\": \"Truncation mutagenesis, in vivo co-immunoprecipitation, in vitro binding assays with purified proteins\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution combined with in vivo Co-IP and multiple truncation mutants, single lab\",\n      \"pmids\": [\"17300223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Extracellular/secreted STI1 induces proliferation of human glioblastoma cells (A172) via MAPK (ERK) and PI3K signaling pathways, and this effect involves cellular prion protein (PrPC).\",\n      \"method\": \"Thymidine incorporation assay, pathway inhibitor experiments, extracellular STI1 application\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pharmacological inhibitors only, no direct binding assay reported\",\n      \"pmids\": [\"17886292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Interaction of PrPC with hop/STI1 induces loss of PrP helical structures (perturbation of PrP helix 143–153) and a C-terminal compaction of hop/STI1, as revealed by CD, fluorescence spectroscopy, and SAXS; free murine hop/STI1 is monomeric by both SAXS and size-exclusion chromatography.\",\n      \"method\": \"Circular dichroism (CD), fluorescence spectroscopy, small angle X-ray scattering (SAXS), size-exclusion chromatography\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple biophysical methods (CD, SAXS) on recombinant proteins, single lab\",\n      \"pmids\": [\"19703931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Deletion of STI1 in yeast both suppresses Ssa1-21 (Hsp70 mutant)-mediated impairment of [PSI+] and blocks Hsp104-mediated curing of [PSI+] prions; Sti1 variants defective in Hsp70 or Hsp90 interaction cure less efficiently, and Hsp90 inhibitor abolishes curing, demonstrating Sti1 acts in prion curing through both Hsp70 and Hsp90 interactions.\",\n      \"method\": \"Genetic epistasis, STI1 deletion, domain-specific mutations, Hsp90 inhibitor treatment, prion-curing assays in yeast\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic epistasis experiments with Hsp70, Hsp90, and Sti1 mutants, replicated across conditions\",\n      \"pmids\": [\"20479121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Sti1/Hop has a modular architecture: TPR2A is the high-affinity Hsp90-binding site; TPR1 and TPR2B bind Hsp70 with moderate affinity; DP1 and DP2 have homologous α-helical folds (determined by NMR); the TPR2A–TPR2B segment is the core Hsp90 inhibitory module; TPR2A and TPR2B are connected by a rigid linker orienting their binding sites in opposite directions, allowing simultaneous binding of TPR2A to Hsp90 C-terminal domain and TPR2B to Hsp70; DP2 is important for client activation in vivo.\",\n      \"method\": \"NMR structure determination of DP domains, crystal structure of TPR2A–TPR2B segment, in vitro binding assays, in vivo client activation assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure, NMR, and functional validation in one study, multiple orthogonal methods\",\n      \"pmids\": [\"22227520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Sti1 stabilizes multiple regions in all three domains of Hsp90 and slows dimer dissociation; it inhibits Hsp90 ATPase by preventing N-terminal dimerization and docking of the N-terminal with the middle domain; crosslinking-MS identified Sti1 segments in close proximity to the Hsp90 N-terminal domain; the linker length between Hsp90 C-terminal dimerization domain and MEEVD motif is important for Sti1 association rates.\",\n      \"method\": \"Hydrogen exchange mass spectrometry (HX-MS), crosslinking mass spectrometry, mutant Hsp90 analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — HX-MS and crosslinking-MS provide conformational dynamics data, two orthogonal biophysical methods, single lab\",\n      \"pmids\": [\"22354036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Sti1 modulates spatial quality control of amyloid-like proteins (Htt103Q, Rnq1) in yeast cytosol: loss of Sti1 exacerbates Htt toxicity and hinders foci formation; elevation of Sti1 suppresses toxicity and organizes small Htt103Q foci into larger perinuclear assemblies containing thioflavin-T-positive amyloid-like material.\",\n      \"method\": \"High-copy suppressor screen in yeast, fluorescence microscopy, thioflavin-T staining, toxicity assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic screen plus multiple functional readouts and imaging, single lab\",\n      \"pmids\": [\"24109600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Sti1/Hop is a dynamic elongated protein with a flexible N-terminal module and rigid C-terminal module; without Hsp90, Sti1 is more compact and TPR2B is the high-affinity Hsp70-binding site; in the presence of Hsp90, Hsp70 shifts its preference away from TPR2B; the linker connecting the two modules is crucial for Hsp70 interaction and client activation in vivo.\",\n      \"method\": \"Single-molecule fluorescence (FRET), NMR, truncation mutants, in vivo client activation assays, fluorescence cross-correlation spectroscopy\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — single-molecule FRET plus NMR plus functional assays, multiple orthogonal methods\",\n      \"pmids\": [\"25851214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Cytoplasmic STI1 directly interacts with the small GTPase Rnd1; this interaction is specific for Rnd1 (not other Rnd family members); STI1 overexpression prevents Rnd1-plexin-A1-mediated cytoskeleton retraction in COS collapse assay and enhances neurite outgrowth in PC-12 cells.\",\n      \"method\": \"Co-immunoprecipitation, COS cell collapse assay, PC-12 neurite outgrowth assay, specificity tests with Rnd family members\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus two functional assays with specificity controls, single lab\",\n      \"pmids\": [\"24690281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Yeast Sti1 is phosphorylated at inhibitory sites; human Hop is also subject to inhibitory phosphorylation; phospho-mimetic variants of Hop have reduced ability to activate clients in vivo, reduced affinity for Hsp70, and reduced interaction with Hsp90 (for human Hop), inducing structural rearrangements in the protein core.\",\n      \"method\": \"Phospho-mimetic mutagenesis, in vivo client activation assays, affinity binding assays, structural analysis\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phospho-mimetic mutations plus functional and binding assays, both yeast and human proteins tested, single lab\",\n      \"pmids\": [\"25504578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"STIP1 co-immunoprecipitates with actin from HEK293T cells and directly interacts with actin in vitro via its C-terminal TPR2AB-DP2 domain; STIP1 can stimulate actin ATPase activity in vitro; STIP1 depletion leads to increased nuclear actin accumulation, F-actin disorganization, and altered cofilin/profilin levels.\",\n      \"method\": \"Co-immunoprecipitation from HEK293T cells, in vitro direct binding/ATPase assay, STIP1 knockdown with fluorescence imaging of actin structures, western blot for cofilin and profilin\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding and ATPase assay plus cellular imaging and Co-IP, single lab\",\n      \"pmids\": [\"32365744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"STIP1 interacts with the Axin scaffold protein, enhances the Axin–DVL2 interaction, and thereby activates β-catenin/TCF (Wnt) signaling in hepatocellular carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation, STIP1 knockdown/overexpression with downstream Wnt reporter\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP and KD/OE functional assay, single lab\",\n      \"pmids\": [\"29596884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"STIP1 domains DP1, TPR1, and TPR2A all contribute to PrPC binding: DP1 binds the N-terminal region of PrP (residues 23–95), TPR1 and TPR2A bind the C-terminal region (residues 90–231); only TPR1 and TPR2A directly inhibit AβO binding to PrPC and AβO-induced neuronal cell death; the TPR2A–PrP interface is extensive and partially overlaps with the Hsp90-binding site, suggesting a PrP–STIP1–Hsp90 ternary complex.\",\n      \"method\": \"NMR chemical shift mapping, binding domain mapping with truncated STIP1 constructs, cell death assays, amyloid-beta oligomer competition binding assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structural mapping plus functional cell death assays, single lab\",\n      \"pmids\": [\"27208175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Deletion of STI1 in yeast causes alterations in mitochondrial morphology and lower steady-state levels of a subset of mitochondrial proteins; double deletion of STI1 with mitochondrial import factors MIM1 or TOM20 shows synthetic growth phenotype; recombinant cytosolic domains of Tom20 and Tom70 bind Sti1 in vitro, suggesting Sti1 plays a direct or indirect role in mitochondrial protein import.\",\n      \"method\": \"Site-directed photo-crosslinking in yeast, genetic epistasis (double deletion growth assays), in vitro binding assay with Tom receptor domains, mitochondrial morphology imaging\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — photo-crosslinking, genetic epistasis, and in vitro binding assays, single lab\",\n      \"pmids\": [\"27412066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Three S100A1 dimers associate with one STIP1 molecule in a calcium-dependent manner; each STIP1 TPR domain (TPR1, TPR2A, TPR2B) binds one S100A1 dimer with different affinities (TPR2B highest); S100A1 binds each TPR domain through a common interface (α-helices III and IV) accessible only after calcium-induced conformational change; TPR2B binding involves insertion of S100A1 into its hydrophobic cleft.\",\n      \"method\": \"Isothermal titration calorimetry (ITC), domain-specific binding assays with isolated TPR domains, calcium-dependence studies\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — ITC quantitative binding with multiple domain constructs, stoichiometry defined, single lab with rigorous controls\",\n      \"pmids\": [\"28408431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Hop/STIP1 depletion or overexpression reduces emerin protein levels via proteasomal and lysosomal pathways; Hop and emerin co-immunoprecipitate in a complex that also contains Hsp70 but not Hsp90; TPR2AB domain of Hop is required for the Hop-emerin association; loss of Hop or emerin causes nuclear deformation and decreased nuclear size; nuclear defects from Hop loss are rescued by emerin overexpression.\",\n      \"method\": \"Co-immunoprecipitation, STIP1 depletion/overexpression, proteasome/lysosome inhibitor experiments, nuclear morphology imaging, rescue experiment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus domain mapping and phenotypic rescue, single lab\",\n      \"pmids\": [\"30449594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Human cell lines and budding yeast with deletion of STIP1/STI1 display reduced proteasome activity due to inefficient capping of the 20S core particle with regulatory particles; unexpectedly, knockout cells are more proficient at preventing protein aggregation and promoting protein refolding, because a more efficient prokaryote-like Hsp70–Hsp90 binary complex (without Hop restraint) compensates; this was also demonstrated in vitro.\",\n      \"method\": \"Gene knockout in human cells and yeast, in vitro reconstitution of Hsp70–Hsp90 chaperone activity, proteasome activity assays, protein aggregation/refolding assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution plus KO in two organisms, multiple orthogonal assays, significant mechanistic insight\",\n      \"pmids\": [\"33239621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"STI1 co-immunoprecipitates α-synuclein; NMR analyses show direct interaction of α-synuclein with the TPR2A domain (but not TPR1 or TPR2B) of STI1, involving the C-terminal domain of α-synuclein; the STI1 TPR2A domain facilitates S129 phosphorylation of α-synuclein by Polo-like kinase 3 in vitro; mice over-expressing STI1 and Hsp90β show elevated S129 α-synuclein phosphorylation and inclusion formation; reduced STI1 function decreases inclusion formation and phosphorylation while mitigating motor and cognitive deficits.\",\n      \"method\": \"Co-immunoprecipitation, NMR interaction mapping, in vitro phosphorylation assay with PLK3, mouse model with altered STI1 expression\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — NMR direct interaction mapping plus in vitro kinase assay plus in vivo mouse models, multiple orthogonal methods\",\n      \"pmids\": [\"36121476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Hsp90 and its co-chaperone Sti1 modulate TDP-43 misfolding, inclusion formation, aggregation, and cellular toxicity; Sti1 specifically interacts with TDP-43 and strongly modulates TDP-43 toxicity in a dose-dependent manner in yeast and mammalian neuronal cells.\",\n      \"method\": \"Co-immunoprecipitation, TDP-43 aggregation assay, toxicity assays in yeast and mammalian neuronal cells, genetic manipulations of STI1/Hsp90\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional toxicity and aggregation assays in two systems, single lab\",\n      \"pmids\": [\"33908654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"STIP1 can be isolated in a complex with actin and Hsp90 from HEK293T cells; STIP1 directly interacts with actin via the C-terminal TPR2AB-DP2 domain in vitro; STIP1 can stimulate the in vitro ATPase activity of actin.\",\n      \"method\": \"Co-immunoprecipitation, in vitro direct binding assay, in vitro ATPase stimulation assay\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro assay plus Co-IP, single lab\",\n      \"pmids\": [\"32365744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"JAK2 phosphorylates STIP1 at tyrosine residues Y134 and Y152, promoting STIP1 protein stability, inducing nuclear-cytoplasmic shuttling, and promoting STIP1 secretion into the extracellular space; JAK2-mediated STIP1 phosphorylation enhances cell viability and increases resistance to cisplatin-induced cell death; disrupting STIP1–JAK2 interaction decreases JAK2 protein levels.\",\n      \"method\": \"Site-directed mutagenesis of phosphorylation sites, cell-penetrating inhibitory peptides, immunoblotting for stability, nuclear-cytoplasmic fractionation, ELISA for secretion, cell viability assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-directed mutagenesis plus functional assays (viability, localization, secretion), single lab\",\n      \"pmids\": [\"35269562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"STIP1 binds to HSP40, HSP70, and HSP90 in rat H9c2 cardiomyocytes; overexpression of STIP1 promotes the transition of Cx43 from Cx43-HSP70 to Cx43-HSP90 complexes and inhibits Cx43 ubiquitination; knockdown of STIP1 has the opposite effect; HSP90 inhibition counteracts the inhibitory effect of STIP1 overexpression on Cx43 ubiquitination.\",\n      \"method\": \"Co-immunoprecipitation, STIP1 overexpression/knockdown, HSP90 inhibitor treatment, ubiquitination assays in H9c2 cardiomyocytes\",\n      \"journal\": \"Cytotechnology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional ubiquitination assay with gain/loss-of-function and HSP90 inhibitor, single lab\",\n      \"pmids\": [\"37187948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The lncRNA LINC01226 binds STIP1 protein, leads to disassembly of the STIP1–HSP90 complex, elevates HSP90–β-catenin interactions, stabilizes β-catenin protein, and activates Wnt/β-catenin signaling to promote gastric cancer progression.\",\n      \"method\": \"RNA-protein pulldown, co-immunoprecipitation, LINC01226 overexpression/knockdown with downstream β-catenin/TCF assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — RNA-protein interaction and Co-IP, but mechanistic evidence for complex disassembly is indirect, single lab\",\n      \"pmids\": [\"37806517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"During proteostatic stress, Sti1 forms cytoplasmic inclusions in yeast and mammalian cells that overlap with misfolded proteins; deletion of STI1 causes accumulation of soluble misfolded ubiquitinated proteins and activates the heat shock response; Sti1 sequesters misfolded proteins during stress independently of its Hsp90 ATPase regulatory function.\",\n      \"method\": \"Fluorescence imaging of inclusions in yeast and mammalian cells, soluble/insoluble protein fractionation, ubiquitin accumulation assay, heat shock reporter assay, STI1 deletion\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cellular imaging plus biochemical fractionation and reporter assay, two organisms tested, single lab\",\n      \"pmids\": [\"39739753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The mitochondrial targeting signal (MTS) directly engages the co-chaperones of Hsc70 including Stip1/HOP via site-specific photo-crosslinking; STIP1/Hop and St13 facilitate chaperone retention on the mature domain of mitochondrial precursor proteins; during acute import stress, this Hsp90 co-chaperone interaction (requiring the MTS) buffers precursor degradation and maintains import competence.\",\n      \"method\": \"Site-specific photo-crosslinking in cells, biochemical reconstitution, import stress experiments\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — photo-crosslinking and biochemical reconstitution in single preprint study\",\n      \"pmids\": [\"bio_10.1101_2025.01.18.633710\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"STIP1/HOP directly interacts with α-synuclein via two binding motifs in the C-terminus of α-synuclein that dynamically compete for the TPR2A domain of STIP1; STIP1 binding attenuates α-synuclein fibril formation while promoting accumulation of high-molecular-weight amorphous and A11-positive oligomeric species that are more cytotoxic to neuronal cells.\",\n      \"method\": \"NMR interaction mapping, in vitro aggregation assays, A11 oligomer dot-blot, neuronal cell viability assays\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR mapping plus in vitro aggregation and cytotoxicity assays, single preprint\",\n      \"pmids\": [\"bio_10.1101_2025.03.26.645247\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"STIP1 interacts with adenosylhomocysteinase (AHCY/SAHH) and changes AHCY conformation; STIP1 facilitates AHCY binding to lactate dehydrogenase A (LDHA), stimulating glycolysis; AHCY then recruits PRMT3 to methylate LDHA at R106, inhibiting ubiquitination-mediated AHCY degradation; STIP1 knockout in mice inhibits 4NQO-induced esophageal tumorigenesis.\",\n      \"method\": \"Co-immunoprecipitation, conformational assay, in vivo mouse knockout, glycolysis assays, methylation assays\",\n      \"journal\": \"Exploration (Beijing, China)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Co-IP plus in vivo KO, but pathway mechanism is complex and reported in a single study with limited mechanistic reconstitution\",\n      \"pmids\": [\"41163796\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"STIP1/Hop/Sti1 is a modular co-chaperone that simultaneously bridges Hsp70 (via TPR1 and TPR2B) and Hsp90 (via TPR2A) to facilitate client protein transfer between these chaperones; it non-competitively inhibits the Hsp90 ATPase by blocking N-terminal Hsp90 dimerization; its activity is negatively regulated by phosphorylation at species-specific inhibitory sites; beyond its canonical chaperone scaffolding role, STIP1 can independently sequester misfolded proteins during acute stress, regulates proteasome assembly, directly interacts with cellular prion protein (PrPC) to modulate neuronal signaling and neuroprotection, directly binds α-synuclein via its TPR2A domain to promote formation of cytotoxic oligomers, interacts with actin to regulate cytoskeletal dynamics, and can act as a scaffold for signaling complexes including JAK/STAT3 pathways.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"STIP1 (Hop/Sti1) is a modular co-chaperone adaptor that physically bridges the Hsp70 and Hsp90 chaperone machines to coordinate the maturation of client proteins, a role first established genetically in yeast where Sti1 acts at an intermediate step downstream of Hsp70 (Ydj1) and upstream of mature Hsp90-client complexes [#1]. It engages the two chaperones through distinct tetratricopeptide repeat (TPR) domains: TPR2A is the high-affinity Hsp90-binding site while TPR1 and TPR2B bind Hsp70, and client folding requires Sti1 to bridge both chaperones simultaneously [#4, #12]. Structurally, Sti1/Hop is an elongated, conformationally dynamic protein in which a rigid TPR2A–TPR2B linker orients the two binding sites in opposite directions to permit concurrent Hsp70 and Hsp90 engagement, with Hsp90 binding shifting Hsp70 away from TPR2B [#12, #15]. Functionally, STIP1 acts as a non-competitive inhibitor of the Hsp90 ATPase, binding both N- and C-terminal regions of Hsp90, stabilizing its domains, and preventing the N-terminal dimerization and N–middle domain docking required for ATP hydrolysis [#3, #13]; this restraining activity is itself negatively regulated by inhibitory phosphorylation that reduces chaperone affinity and client activation [#17]. By restraining Hsp70–Hsp90 complex formation, STIP1 also governs downstream proteostasis outcomes — its loss reduces 20S proteasome capping and proteasome activity yet paradoxically improves aggregation prevention and refolding via a more efficient Hsp70–Hsp90 binary complex [#24] — and during proteostatic stress STIP1 independently sequesters misfolded ubiquitinated proteins into cytoplasmic inclusions in a manner separable from its Hsp90 ATPase regulatory function [#31]. Beyond canonical chaperoning, STIP1 directly binds cellular prion protein (PrPC) through DP1, TPR1, and TPR2A to support neuroprotective signaling and to block amyloid-β oligomer binding [#5, #20], and it directly engages α-synuclein via its TPR2A domain, facilitating PLK3-mediated S129 phosphorylation and promoting cytotoxic oligomeric species in vivo [#25]. STIP1 additionally functions as a scaffold in JAK–STAT3 signaling [#2], binds actin and stimulates its ATPase to regulate cytoskeletal organization [#18], and contributes to mitochondrial precursor import [#21].\",\n  \"teleology\": [\n    {\n      \"year\": 1989,\n      \"claim\": \"Established STIP1's founding identity as a stress-inducible factor before any chaperone role was known, linking it to the heat shock response.\",\n      \"evidence\": \"Gene disruption and overexpression with HSP70 promoter reporter in yeast\",\n      \"pmids\": [\"2674681\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular mechanism for HSP70 promoter trans-activation defined\", \"Direct chaperone partners not yet identified\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Placed Sti1 mechanistically within the Hsp70-to-Hsp90 client maturation pathway, defining it as an intermediate co-chaperone rather than an independent factor.\",\n      \"evidence\": \"Genetic epistasis with hsp90ts mutants and client (GR, v-Src) activity/Co-IP assays in yeast\",\n      \"pmids\": [\"8972212\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Domain basis for dual chaperone engagement not yet resolved\", \"Biochemical effect on Hsp90 enzymatic activity unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified a chaperone-independent scaffolding role linking STIP1 to JAK–STAT3 signaling, broadening its functional scope.\",\n      \"evidence\": \"Co-IP, dominant-negative domain overexpression, and STAT3 reporter/translocation assays\",\n      \"pmids\": [\"10954736\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether scaffolding requires chaperone activity not addressed\", \"Single lab, no structural mapping of the STAT3-binding region\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined the biochemical mechanism of Hsp90 regulation, showing STIP1 non-competitively inhibits the ATPase by blocking N-terminal dimerization.\",\n      \"evidence\": \"Reconstituted in vitro ATPase assays and binding to truncated Hsp90 constructs\",\n      \"pmids\": [\"12525481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the inhibitory module not yet available\", \"Coupling to client transfer not directly shown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Assigned division of labor among Sti1 TPR domains, showing TPR1 governs Hsp70 and TPR2A/TPR2B govern Hsp90 regulation independently.\",\n      \"evidence\": \"Domain-specific mutagenesis with [PSI+] prion and Hsp90-inhibitor functional assays in yeast\",\n      \"pmids\": [\"16100115\", \"16219779\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"DP2 essential function mechanistically unexplained\", \"Redundancy vs specialization of TPR1/TPR2B not fully resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Extended STIP1 function to extracellular neuronal signaling by demonstrating direct PrPC interaction driving neuroprotection.\",\n      \"evidence\": \"Co-IP, inhibitory peptide competition, and SOD/cell survival assays in neuronal cells\",\n      \"pmids\": [\"15670743\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding interface not mapped at residue level\", \"Downstream signaling cascade incompletely defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Refined the domain model, showing TPR1/TPR2B redundancy for Hsp70 and that TPR2A drives both Hsp90 binding and Sti1 dimerization while DP2 is dispensable for interactions but essential in vivo.\",\n      \"evidence\": \"Truncation mutagenesis with in vivo Co-IP and in vitro binding; nucleotide-dependence Co-IP with Hsp90 mutants\",\n      \"pmids\": [\"17300223\", \"17101799\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo essential role of DP2 still mechanistically unexplained\", \"Conformational coupling between domains not yet visualized\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated that Sti1 acts in prion propagation/curing through both its Hsp70 and Hsp90 interactions, integrating its dual-chaperone role into amyloid handling.\",\n      \"evidence\": \"Genetic epistasis, domain mutants, and Hsp90 inhibitor in yeast [PSI+] curing assays\",\n      \"pmids\": [\"20479121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct action on prion substrate vs chaperone modulation not separated\", \"Relevance to mammalian amyloids not tested here\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Provided the structural basis for simultaneous dual-chaperone bridging and the core Hsp90 inhibitory module, unifying earlier domain genetics.\",\n      \"evidence\": \"Crystal structure of TPR2A–TPR2B, NMR of DP domains, binding and client activation assays; HX-MS and crosslinking-MS of the Hsp90 complex\",\n      \"pmids\": [\"22227520\", \"22354036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length Hop–Hsp70–Hsp90 ternary structure not solved\", \"Dynamics of client handoff not captured\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed STIP1 as a conformationally dynamic adaptor whose Hsp70 preference is allosterically reset by Hsp90 binding, and expanded its roles to spatial protein quality control, cytoskeletal regulation, and inhibitory phosphorylation.\",\n      \"evidence\": \"Single-molecule FRET and NMR; yeast Htt/Rnq1 suppressor and imaging assays; Rnd1 Co-IP with collapse/neurite assays; phospho-mimetic mutagenesis\",\n      \"pmids\": [\"25851214\", \"24109600\", \"24690281\", \"25504578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological kinases for inhibitory sites not identified here\", \"Mechanistic link between adaptor dynamics and quality-control function unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Mapped the PrPC-binding architecture and showed STIP1 blocks amyloid-β oligomer toxicity, while uncovering additional partners in cytoskeleton, nuclear envelope, mitochondrial import, and Wnt signaling.\",\n      \"evidence\": \"NMR chemical-shift mapping with PrP/AβO assays; actin Co-IP/ATPase and imaging; emerin Co-IP, domain mapping and rescue; Tom20/Tom70 binding and yeast genetics; Axin Co-IP/Wnt reporter\",\n      \"pmids\": [\"27208175\", \"32365744\", \"30449594\", \"27412066\", \"29596884\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether non-chaperone partners require Hsp70/Hsp90 engagement not resolved\", \"Several interactions rest on single-lab Co-IP without reciprocal structural validation\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Quantified calcium-dependent S100A1 engagement of all three TPR domains, defining STIP1 as a calcium-responsive multivalent TPR hub.\",\n      \"evidence\": \"Isothermal titration calorimetry with isolated TPR domains and calcium-dependence studies\",\n      \"pmids\": [\"28408431\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of S100A1 binding for chaperone cycle untested\", \"Cellular context of the interaction undefined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved how loss of STIP1 reshapes proteostasis, showing it is required for proteasome capping yet restrains an intrinsically efficient Hsp70–Hsp90 binary complex.\",\n      \"evidence\": \"Knockout in human cells and yeast plus in vitro reconstitution of chaperone activity and proteasome/refolding assays\",\n      \"pmids\": [\"33239621\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of proteasome capping defect not detailed\", \"When the binary complex is advantageous in vivo unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established direct, TPR2A-specific engagement of disease-associated aggregating proteins, mechanistically linking STIP1 to synucleinopathy and TDP-43 proteinopathy.\",\n      \"evidence\": \"Co-IP, NMR mapping, in vitro PLK3 kinase assay and STI1-altered mouse models for α-synuclein; Co-IP and aggregation/toxicity assays for TDP-43\",\n      \"pmids\": [\"36121476\", \"33908654\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether STIP1 promotes or detoxifies aggregates context-dependent and not fully reconciled\", \"TDP-43 binding interface not mapped\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Linked STIP1-directed Hsp70-to-Hsp90 client handoff to substrate stabilization in disease-relevant contexts and to oncogenic Wnt signaling.\",\n      \"evidence\": \"Co-IP, gain/loss-of-function and Hsp90 inhibitor with Cx43 ubiquitination in cardiomyocytes; lncRNA pulldown/Co-IP with β-catenin assays\",\n      \"pmids\": [\"37187948\", \"37806517\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"LINC01226-driven complex disassembly evidence is indirect\", \"Generality across substrates not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Sharpened the mechanistic picture of STIP1 in mitochondrial import buffering, α-synuclein oligomer toxicity, and a metabolic AHCY/LDHA axis driving tumorigenesis.\",\n      \"evidence\": \"Photo-crosslinking and reconstitution for MTS-driven import (preprint); NMR/aggregation/cytotoxicity for α-synuclein (preprint); Co-IP, glycolysis/methylation assays and mouse KO for AHCY/LDHA\",\n      \"pmids\": [\"bio_10.1101_2025.01.18.633710\", \"bio_10.1101_2025.03.26.645247\", \"41163796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Two findings are preprints awaiting peer review\", \"AHCY/LDHA metabolic pathway rests on a single low-confidence study with limited reconstitution\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How STIP1's many non-canonical activities (cytoskeletal, signaling, metabolic, mitochondrial) mechanistically relate to its core Hsp70/Hsp90 bridging function remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model distinguishing chaperone-dependent from chaperone-independent functions\", \"Physiological kinases regulating inhibitory phosphorylation in vivo not defined\", \"Full-length structure of the Hop–Hsp70–Hsp90 client complex not solved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 4, 12, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 13, 24]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [1, 4, 24]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3, 13]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [18, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [16, 18, 31]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [9, 28]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [28]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0008953897\", \"supporting_discovery_ids\": []}\n    ],\n    \"complexes\": [\n      \"Hsp70-Hop-Hsp90 chaperone complex\"\n    ],\n    \"partners\": [\n      \"HSP90\",\n      \"HSP70\",\n      \"PRNP\",\n      \"SNCA\",\n      \"STAT3\",\n      \"ACTB\",\n      \"S100A1\",\n      \"JAK2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}