{"gene":"GORASP1","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":1997,"finding":"GRASP65 is a 65 kDa Golgi membrane protein whose antibodies and recombinant form block cisternal stacking in a cell-free system; it forms a complex with GM130 and is tightly bound to Golgi membranes even under mitotic conditions when both proteins are heavily phosphorylated, linking it to vesicle docking and cisternal stacking.","method":"Cell-free cisternal stacking assay, antibody inhibition, co-immunoprecipitation, biochemical fractionation","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted cell-free stacking assay with antibody/recombinant protein inhibition, replicated across subsequent studies","pmids":["9346242"],"is_preprint":false},{"year":1998,"finding":"The binding site for GRASP65 on GM130 maps to the C-terminal sequence xxNDxxxIMVI of GM130, while the binding site for GM130 on GRASP65 maps to amino acids 189–201 (reminiscent of PDZ domains); interaction of the two proteins is required for correct targeting of both to the Golgi apparatus.","method":"Gel filtration, in vitro translation, site-directed mutagenesis, immunoprecipitation, GFP-reporter targeting assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis combined with binding assays and functional targeting readout in a single rigorous study","pmids":["9628863"],"is_preprint":false},{"year":2000,"finding":"Polo-like kinase (Plk) binds GRASP65 (identified by yeast two-hybrid) and phosphorylates it both in vitro and in vivo; Cdc2 also phosphorylates GRASP65; the conserved C-terminal domain of Plk is required for efficient GRASP65 phosphorylation.","method":"Yeast two-hybrid, in vitro kinase assay, in vivo phosphorylation, deletion/frameshift mutant analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay plus in vivo evidence, replicated by multiple subsequent studies","pmids":["11050165"],"is_preprint":false},{"year":2002,"finding":"GRASP65 is cleaved specifically by caspase-3 at conserved sites in its C-terminus during apoptosis; expression of a caspase-resistant GRASP65 partially preserved cisternal stacking and inhibited Golgi ribbon breakdown in apoptotic cells.","method":"Caspase cleavage assay, expression of caspase-resistant mutants, electron microscopy of Golgi ultrastructure","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro caspase cleavage assay plus mutagenesis rescue experiment with defined structural readout","pmids":["11815631"],"is_preprint":false},{"year":2003,"finding":"GRASP65 is the major phosphorylation target of cdc2-cyclin B and polo-like kinases in rat liver Golgi membranes; these kinases alone can unstack Golgi membranes; GRASP65 homodimers on beads form trans-oligomeric aggregates that are disaggregated by mitotic kinases and re-aggregated after dephosphorylation, demonstrating direct mitotically regulated stacking activity.","method":"In vitro kinase assay, cell-free Golgi disassembly/reassembly assay, bead aggregation assay, microinjection of anti-GRASP65 antibodies","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal in vitro reconstitution methods plus microinjection in living cells","pmids":["12839990"],"is_preprint":false},{"year":2004,"finding":"The N-terminal GRASP domain (aa 1–201) of GRASP65 is necessary and sufficient for dimerization and trans-oligomerization; the C-terminal serine/proline-rich domain (aa 202–446) confers mitotic regulation through phosphorylation sites targeted by cdc2/cyclin B1 and polo-like kinase.","method":"Domain deletion/truncation expression, biochemical oligomerization assays, transient overexpression with Golgi fragmentation readout","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic domain mapping with mutagenesis and functional readout in a single study","pmids":["15576368"],"is_preprint":false},{"year":2005,"finding":"Cdk1-cyclin B phosphorylates GRASP65 at four C-terminal consensus sites, and phosphorylated GRASP65 recruits the polo box domain of Plk1; mutation of these four sites to alanine abolishes mitotic phosphorylation and Plk1 binding; expression of wild-type but not phosphorylation-defective GRASP65 C-terminus delays mitotic entry.","method":"In vitro kinase assay, polo-box domain binding assay, alanine mutagenesis, cell cycle progression assay in NRK cells","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase and binding assays with mutagenesis plus cell-based functional readout","pmids":["15678101"],"is_preprint":false},{"year":2005,"finding":"GRASP65 depletion by RNAi causes metaphase arrest with multiple aberrant spindles; the C-terminus of GRASP65 expressed in cells interferes with mitotic entry, revealing a role for GRASP65 in spindle dynamics and cell cycle control beyond Golgi stacking.","method":"RNAi depletion in HeLa cells, immunofluorescence microscopy of spindle/centrosome markers, C-terminal construct overexpression","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean RNAi with specific cellular phenotype plus expression construct, but mechanism of spindle effect not fully resolved","pmids":["15888544"],"is_preprint":false},{"year":2005,"finding":"GRASP65 is phosphorylated at serine 277 in interphase cells in response to serum/EGF directly by ERK; during mitosis Ser-277 is phosphorylated by Cdk1 instead of ERK; microinjection of a GRASP65 fragment containing Ser-277 inhibits mitosis passage, an effect abolished by S277A mutation.","method":"In vitro kinase assay, phospho-specific antibody, microinjection of recombinant protein/peptide fragments, alanine mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assays with phospho-specific antibodies plus functional microinjection rescue experiment","pmids":["15834132"],"is_preprint":false},{"year":2006,"finding":"Golgi ribbon formation (lateral cisternal fusion) requires both GM130 and GRASP65; these GM130- and GRASP65-dependent fusion events are necessary for uniform enzyme distribution across the Golgi ribbon.","method":"RNAi knockdown, quantitative fluorescence microscopy of Golgi ribbon, enzyme distribution assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — RNAi with multiple functional readouts, replicated in subsequent studies","pmids":["16489344"],"is_preprint":false},{"year":2007,"finding":"The yeast GRASP65 orthologue Grh1 associates with the cis-Golgi via an N-terminal amphipathic helix that is N-terminally acetylated; Grh1 forms a complex with the coiled-coil protein Bug1 (Ydl099w); Grh1 interacts with the COPII coat component Sec23/24; genetic interactions with Uso1 and Ypt1 suggest the Grh1-Bug1 complex contributes to COPII vesicle consumption and cis-Golgi formation.","method":"Biochemical fractionation, co-immunoprecipitation, genetic interaction analysis, functional assays","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus genetic epistasis in yeast, single lab","pmids":["17261844"],"is_preprint":false},{"year":2008,"finding":"EGF or LPA stimulation activates ERK, which phosphorylates GRASP65 at serine 277; a S277A or 1–201 truncation mutant (non-phosphorylatable by ERK) prevents Golgi orientation to the leading edge and inhibits centrosome orientation during directed cell migration; ERK phosphorylation of GRASP65 causes loss of GRASP65 oligomerization and Golgi cisternal unstacking.","method":"In vitro ERK kinase assay, phospho-specific antibody, expression of phospho-mutants, wound-healing migration assay, brefeldin A rescue","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus multiple functional readouts (migration, oligomerization, stacking) with mutagenesis","pmids":["18762583"],"is_preprint":false},{"year":2009,"finding":"GRASP65 PDZ domains directly bind C-terminal valine-bearing cargo receptors (CD8α and Frizzled4); both GRASP65 and GRASP55 are needed sequentially for efficient transport of these receptors to and through the Golgi complex.","method":"Direct binding assay (PDZ-cargo interaction), RNAi depletion, protein trafficking assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay plus RNAi trafficking readout, single lab","pmids":["19840934"],"is_preprint":false},{"year":2010,"finding":"The first 112 amino acids of GRASP65 (including PDZ1) are sufficient for oligomerization; expression of non-regulatable GRASP65 mutants enhances Golgi stacking in interphase and inhibits fragmentation during mitosis; GRASP65 siRNA reduces cisternae per stack and is rescued by exogenous GRASP65; inhibiting mitotic Golgi disassembly with non-regulatable GRASP65 delayed mitotic entry and suppressed cell growth, an effect rescued by brefeldin A-induced Golgi dispersal.","method":"Domain truncation analysis, electron microscopy of Golgi ultrastructure, siRNA depletion with rescue, brefeldin A treatment, cell cycle assays","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — systematic domain analysis, EM readout, siRNA rescue, and functional cell cycle assay in a single study","pmids":["20214750"],"is_preprint":false},{"year":2010,"finding":"GRASP65 links cis-Golgi cisternae via a homotypic N-terminal PDZ interaction; PLK1 phosphorylates a site within the GRASP65 N-terminal domain proximate to an internal PDZ ligand; phospho-mimetic mutation at this site blocks organelle tethering, while alanine substitution prevents mitotic Golgi unlinking; an internal PDZ ligand adjacent to the PLK1 site is required for GRASP65 self-interaction.","method":"In vitro PLK1 kinase assay, phospho-mimetic and alanine mutagenesis, organelle tethering assay, interaction assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with mutagenesis directly tested in functional tethering assay","pmids":["20937827"],"is_preprint":false},{"year":2010,"finding":"Simultaneous siRNA knockdown of both GRASP55 and GRASP65 leads to disassembly of the entire Golgi stack, whereas depletion of either alone only reduces the number of cisternae per stack; GRASP65 stacks membranes via oligomerization of its N-terminal GRASP domain, regulated by C-terminal phosphorylation.","method":"siRNA double knockdown, electron microscopy, phospho-mutant expression","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic siRNA epistasis with EM readout, replicated and extended by subsequent CRISPR studies","pmids":["20083603"],"is_preprint":false},{"year":2010,"finding":"Caspase-3 cleavage of GRASP65 during Fas/CD95-mediated apoptosis is required for apoptotic progression; C-terminal caspase-cleavage fragments of GRASP65 are targeted to mitochondria and sensitize cells to Fas ligand; Bcl-XL was identified as a candidate apoptotic binding partner for GRASP65 C-terminal fragments.","method":"Caspase-resistant mutant expression, caspase cleavage assays, subcellular fractionation/localization, co-immunoprecipitation with Bcl-XL","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional mutant expression plus localization, but Bcl-XL interaction is a single Co-IP, single lab","pmids":["21368855"],"is_preprint":false},{"year":2012,"finding":"GRASP65 is sequentially phosphorylated during mitosis: cdc2 phosphorylates T220/T224, S277, and S376; Plk1 enhances these phosphorylations. T220/T224 is phosphorylated from prophase through anaphase; S277 and S376 from late G2 through telophase; T220A/T224A mutation inhibits mitotic Golgi fragmentation more strongly than S277A or S376A mutations; T220/224 dephosphorylation in cytokinesis precedes S277 but follows S376 dephosphorylation.","method":"Phospho-specific antibody generation, in vitro kinase assay, phospho-resistant mutant expression, immunofluorescence microscopy","journal":"Biology open","confidence":"High","confidence_rationale":"Tier 1 / Moderate — phospho-specific antibodies with in vitro kinase validation and mutant functional assays","pmids":["23259055"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of the GRASP65 GRASP domain reveals a dimer in which PDZ2 binding pockets face each other, with the C-terminal tail of one GRASP domain inserting into the PDZ1 pocket of another dimer; both contacts are individually weak but are required in combination for GRASP-mediated Golgi stacking.","method":"X-ray crystallography (GRASP65 GRASP domain structure), biochemical binding assays, mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with biochemical validation and mutagenesis in a single study","pmids":["23940043"],"is_preprint":false},{"year":2014,"finding":"In GRASP65 knockout mice, the Golgi ribbon appears morphologically normal, but FRAP reveals functional discontinuities in the cis-cisternal membrane network; loss of GRASP65 causes changes in plasma membrane glycosylation (GSII lectin staining) in tissues, demonstrating GRASP65 is required for cis-Golgi network continuity and proper glycosylation but is not essential for organism viability.","method":"Homologous recombination knockout, FRAP, GSII lectin staining, electron microscopy","journal":"Biology open","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with FRAP functional assay and biochemical glycosylation readout","pmids":["24795147"],"is_preprint":false},{"year":2015,"finding":"JNK2 phosphorylates GRASP65 at Ser277 during G2, which is essential for separation of Golgi stacks and ribbon unlinking required for mitotic entry; JNK inhibition or JNK2 RNAi causes G2 cell cycle block; this block is bypassed by brefeldin A-induced Golgi dispersal or GRASP65 depletion; JNK2 is required for cleavage of tubules connecting Golgi stacks as measured by FRAP.","method":"RNAi knockdown of JNK2, JNK inhibitors, FRAP, brefeldin A rescue, cell cycle analysis","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal approaches (RNAi, pharmacological, epistasis) with FRAP functional readout","pmids":["25948586"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of GRASP65 PDZ domains in complex with the GM130 C-terminal peptide (1.96 Å) shows that GM130 binds GRASP65 at two distinct sites concurrently, engaging both PDZ1 and PDZ2 domains (contradicting prior models of PDZ2-only interaction); mutagenesis confirms both contacts are required for GRASP65-GM130 association.","method":"X-ray crystallography, site-directed mutagenesis, co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with mutagenesis validation in a single rigorous study","pmids":["26363069"],"is_preprint":false},{"year":2015,"finding":"The actin elongation factor Mena is a GRASP65-binding protein identified by biochemical methods; Mena is recruited to Golgi membranes through interaction with GRASP65; depletion of Mena or disruption of actin polymerization causes Golgi fragmentation; in vitro, Mena and microfilaments enhance GRASP65 oligomerization and Golgi membrane fusion.","method":"Co-immunoprecipitation, Golgi membrane recruitment assay, siRNA depletion, in vitro Golgi fusion assay","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus in vitro reconstitution and siRNA functional readout, single lab","pmids":["26538023"],"is_preprint":false},{"year":2016,"finding":"HCMV-induced Golgi ribbon fragmentation during virion assembly compartment formation is dependent on phosphorylation of GRASP65; inhibition of Golgi membrane fragmentation reduces infectious particle production and alters virion envelope protein incorporation.","method":"Pharmacological inhibition of GRASP65 phosphorylation, infectious virus yield assay, virion protein incorporation analysis","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition with two functional readouts (viral yield and envelope protein incorporation), single lab","pmids":["27703074"],"is_preprint":false},{"year":2017,"finding":"CRISPR/Cas9 double knockout of GRASP55 and GRASP65 in HeLa and HEK293 cells disperses the Golgi stack into single cisternae and tubulovesicular structures, accelerates protein trafficking, and impairs accurate glycosylation of proteins and lipids.","method":"CRISPR/Cas9 knockout, electron microscopy, protein trafficking assays, glycosylation analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR knockout with EM and multiple biochemical functional readouts, extends and confirms prior siRNA work","pmids":["28814501"],"is_preprint":false},{"year":2018,"finding":"DjA1 (DnaJ homolog subfamily A member 1) is a GRASP65-binding protein; depletion of DjA1 causes Golgi fragmentation and delayed Golgi reassembly; immunodepletion of DjA1 from interphase cytosol reduces GRASP65 oligomerization and Golgi membrane fusion in vitro; DjA1 promotes GRASP65 oligomerization through direct interaction independent of its Hsc70 cochaperone activity.","method":"Co-immunoprecipitation, siRNA depletion, in vitro Golgi fusion assay, immunodepletion, purified protein reconstitution","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro reconstitution with purified proteins plus immunodepletion and cell-based rescue","pmids":["30566031"],"is_preprint":false},{"year":2019,"finding":"GRASP65 is required for stabilization of newly nucleated microtubules (leading to their acetylation) and clustering of Golgi stacks; GRASP65 is not involved in microtubule nucleation or anchoring; ribbon formation and microtubule stabilization are both regulated by JNK/ERK-mediated phosphorylation of GRASP65 S274 (human); tubulin acetylation is reduced during G2 as phosphorylation of GRASP65 increases.","method":"RNAi depletion, microtubule regrowth assay, tubulin acetylation immunofluorescence, phospho-mutant expression","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi with multiple mechanistic readouts and phospho-mutant rescue, single lab","pmids":["31336000"],"is_preprint":false},{"year":2021,"finding":"Acute depletion of GRASP65 alone (via degron-tag) does not affect the Golgi ribbon; chronic degradation of GRASP65 does not disrupt ribbon connectivity; acute double depletion of both GRASP55 and GRASP65 causes loss of vesicle tethering proteins GM130, p115, and Golgin-45 from the Golgi and compromises ribbon linking; neither GRASP alone nor both together are required for maintaining stacks or de novo assembly of stacked cisternae after mitosis.","method":"Degron-tag rapid protein degradation, electron microscopy, immunofluorescence for tethering proteins","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — acute degron-mediated depletion (more rigorous than RNAi) with EM and protein localization readouts, contradicts some prior siRNA work","pmids":["33301566"],"is_preprint":false},{"year":2025,"finding":"A human loss-of-function variant in GORASP1 (c.1170_1171del; p.Asp390Glufs*18) causes complete absence of GRASP65 protein and results in a neurodevelopmental Golgipathy; patient cells and CRISPR-engineered RPE cells show hyposialylation (glycosylation defects) and mitotic delay (excess prometaphase/metaphase with polar chromosomes) without Golgi fragmentation.","method":"Patient variant identification, CRISPR/Cas9 recapitulation in RPE cells, glycosylation analysis (hyposialylation), cell cycle/mitosis analysis","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 / Strong — human loss-of-function combined with CRISPR recapitulation in cell model with multiple orthogonal functional readouts","pmids":["39933924"],"is_preprint":false},{"year":2026,"finding":"Protein kinase D2 (PKD2) is an upstream regulator required for GRASP65 phosphorylation at S274 (human) and Golgi ribbon unlinking; PKD2 inhibition or depletion reduces GRASP65-S274 phosphorylation, decreases Golgi unlinking, and delays G2/M transition; PKD2-activating stimuli (phorbol esters, nocodazole) enhance GRASP65 phosphorylation in a PKD2-dependent manner.","method":"Phospho-specific antibody generation, PKD2 inhibitor treatment, siRNA depletion of PKD2, Golgi structure analysis, cell cycle assay","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and genetic PKD2 inhibition with functional GRASP65 phosphorylation and cell cycle readouts, single lab, single paper","pmids":["41892354"],"is_preprint":false}],"current_model":"GRASP65 (GORASP1) is a peripheral cis-Golgi membrane protein that dimerizes and forms trans-oligomers through its N-terminal tandem PDZ (GRASP) domain to physically tether adjacent Golgi cisternae into stacks and link stacks into the Golgi ribbon; it constitutively binds GM130 (via PDZ1/PDZ2 contacts with the GM130 C-terminus) to support vesicle tethering and Golgi targeting; during mitosis, sequential phosphorylation by Cdk1-cyclin B and Plk1 (with PLK1 acting directly on the N-terminal PDZ interaction surface) dissolves GRASP65 oligomers to drive Golgi ribbon unlinking and cisternal unstacking, a process also regulated by ERK/JNK2 phosphorylation of Ser277/S274 upstream of a PKD2-JNK2 signaling axis; caspase-3 cleaves GRASP65 during apoptosis releasing C-terminal mitochondria-targeted fragments that promote cell death; GRASP65 additionally stabilizes newly nucleated microtubules, facilitates transport of C-terminal valine-bearing cargoes through its PDZ domains, and is required for cis-Golgi network continuity and proper glycosylation, with human loss-of-function causing a Golgipathy marked by hyposialylation and mitotic delay."},"narrative":{"mechanistic_narrative":"GORASP1 (GRASP65) is a peripheral cis-Golgi membrane protein that physically tethers and stacks Golgi cisternae and is integrated into mitotic cell-cycle control of Golgi architecture [PMID:9346242, PMID:12839990]. Its N-terminal GRASP domain (PDZ1/PDZ2) is necessary and sufficient for dimerization and trans-oligomerization, the activity that holds adjacent cisternae together [PMID:15576368, PMID:20214750], with a crystallographically defined dimer in which one GRASP domain's C-terminal tail inserts into the PDZ1 pocket of an adjacent dimer—two individually weak contacts that together drive stacking [PMID:23940043]. Through these PDZ domains GRASP65 constitutively binds the C-terminal tail of GM130 at two concurrent sites engaging both PDZ1 and PDZ2, an interaction required for correct Golgi targeting of both proteins and for vesicle tethering [PMID:9628863, PMID:26363069]. GRASP65 together with GM130 mediates lateral cisternal fusion to build the Golgi ribbon and ensure uniform glycosylation enzyme distribution [PMID:16489344], and it acts redundantly with GRASP55: loss of both, but not either alone, disperses the stack and impairs accurate protein and lipid glycosylation [PMID:20083603, PMID:28814501]. Oligomerization is dissolved during mitosis by sequential C-terminal phosphorylation: Cdk1-cyclin B phosphorylates multiple consensus sites and recruits the Plk1 polo-box domain, while PLK1 also acts at an N-terminal site adjacent to an internal PDZ ligand to disrupt self-interaction and unlink the ribbon [PMID:15678101, PMID:20937827, PMID:23259055]; an ERK/JNK2-targeted Ser277/S274 site, downstream of a PKD2 signaling axis, drives interphase and G2 unstacking that governs Golgi orientation during migration and timely mitotic entry [PMID:15834132, PMID:18762583, PMID:25948586, PMID:41892354]. During apoptosis caspase-3 cleaves the C-terminus, releasing mitochondria-targeted fragments that promote cell death [PMID:11815631, PMID:21368855]. GRASP65 additionally facilitates PDZ-dependent transport of C-terminal valine-bearing cargoes [PMID:19840934] and stabilizes newly nucleated microtubules [PMID:31336000]. Human loss-of-function (p.Asp390Glufs*18, absent protein) causes a neurodevelopmental Golgipathy characterized by hyposialylation and mitotic delay without Golgi fragmentation [PMID:39933924].","teleology":[{"year":1997,"claim":"Established GRASP65 as a Golgi membrane protein with direct stacking activity, answering whether a defined factor controls cisternal stacking.","evidence":"Cell-free cisternal stacking assay with antibody/recombinant inhibition and co-IP with GM130","pmids":["9346242"],"confidence":"High","gaps":["Molecular basis of stacking activity not yet resolved","Phosphoregulation defined only as bulk mitotic phosphorylation"]},{"year":1998,"claim":"Mapped the reciprocal GRASP65-GM130 binding sites and showed the interaction targets both proteins to the Golgi, defining the first molecular partner contact.","evidence":"Gel filtration, in vitro translation, site-directed mutagenesis, GFP-reporter targeting","pmids":["9628863"],"confidence":"High","gaps":["Single-site model later revised by structural work","Did not establish stoichiometry or affinity"]},{"year":2000,"claim":"Identified Plk and Cdc2 as the kinases acting on GRASP65, linking it to mitotic kinase cascades.","evidence":"Yeast two-hybrid, in vitro and in vivo kinase assays, Plk deletion mutants","pmids":["11050165"],"confidence":"High","gaps":["Specific phosphosites not yet mapped","Functional consequence on stacking not directly tested here"]},{"year":2002,"claim":"Showed caspase-3 cleaves GRASP65 during apoptosis to drive Golgi breakdown, connecting it to programmed cell death.","evidence":"Caspase cleavage assays, caspase-resistant mutant expression, Golgi EM","pmids":["11815631"],"confidence":"High","gaps":["Fate and function of cleavage fragments not yet defined","Physiological apoptotic trigger not specified"]},{"year":2003,"claim":"Demonstrated directly that mitotic kinases disaggregate GRASP65 trans-oligomers and dephosphorylation re-aggregates them, establishing phospho-regulated oligomerization as the stacking switch.","evidence":"Bead aggregation assay, cell-free Golgi disassembly/reassembly, microinjection of anti-GRASP65 antibody","pmids":["12839990"],"confidence":"High","gaps":["Structural geometry of trans-oligomer unknown","Individual phosphosite contributions unresolved"]},{"year":2004,"claim":"Separated GRASP65 into an N-terminal oligomerization module and a C-terminal phosphoregulatory module, defining domain architecture.","evidence":"Domain deletion/truncation with oligomerization and Golgi fragmentation readouts","pmids":["15576368"],"confidence":"High","gaps":["Atomic structure of GRASP domain not yet available","C-terminal phosphosite identities incomplete"]},{"year":2005,"claim":"Defined the Cdk1-cyclin B four-site phosphorylation that creates the Plk1 polo-box docking platform and gates mitotic entry, establishing the priming-kinase mechanism.","evidence":"In vitro kinase and polo-box binding assays, alanine mutagenesis, cell cycle progression in NRK cells","pmids":["15678101"],"confidence":"High","gaps":["How Golgi unstacking signals back to mitotic entry not mechanistically resolved"]},{"year":2005,"claim":"Revealed a GRASP65 requirement for spindle integrity and cell cycle control beyond Golgi stacking.","evidence":"RNAi depletion in HeLa cells, spindle/centrosome immunofluorescence, C-terminal overexpression","pmids":["15888544"],"confidence":"Medium","gaps":["Mechanism connecting GRASP65 to spindle dynamics not resolved","Indirect effect via Golgi-mitosis checkpoint not excluded"]},{"year":2005,"claim":"Showed Ser277 is an ERK target in interphase but a Cdk1 target in mitosis, identifying a signal-integrating phosphosite.","evidence":"In vitro kinase assays, phospho-specific antibody, microinjection of fragments, S277A mutagenesis","pmids":["15834132"],"confidence":"High","gaps":["Downstream effector of Ser277 phosphorylation not defined here"]},{"year":2006,"claim":"Established that GM130 and GRASP65 jointly mediate lateral cisternal fusion required for ribbon formation and uniform enzyme distribution.","evidence":"RNAi knockdown, quantitative Golgi ribbon imaging, enzyme distribution assays","pmids":["16489344"],"confidence":"High","gaps":["Fusion machinery downstream of tethering not identified","Glycosylation consequences not directly measured"]},{"year":2007,"claim":"Showed the yeast orthologue Grh1 acts at COPII-to-cis-Golgi traffic via Bug1 and Sec23/24, placing GRASP function in early secretory pathway biogenesis.","evidence":"Fractionation, reciprocal co-IP, genetic interaction analysis in yeast","pmids":["17261844"],"confidence":"Medium","gaps":["Conservation of COPII-coupling role in mammalian GRASP65 not tested","Single-lab yeast genetics"]},{"year":2008,"claim":"Linked EGF/LPA-ERK phosphorylation of Ser277 to GRASP65 de-oligomerization and Golgi reorientation during directed cell migration, extending function to interphase polarity.","evidence":"ERK kinase assay, phospho-mutants, wound-healing migration, brefeldin A rescue","pmids":["18762583"],"confidence":"High","gaps":["How Golgi unstacking promotes centrosome/Golgi orientation mechanistically unclear"]},{"year":2009,"claim":"Identified PDZ-dependent binding of C-terminal valine cargo receptors, assigning GRASP65 a direct cargo-transport role.","evidence":"Direct PDZ-cargo binding assay, RNAi depletion, trafficking assays","pmids":["19840934"],"confidence":"Medium","gaps":["Generality of valine-motif cargo selection not established","Single-lab evidence"]},{"year":2010,"claim":"Resolved that non-regulatable GRASP65 enhances stacking and blocks mitotic fragmentation, and that Golgi disassembly is needed for timely mitotic entry, tying organelle inheritance to cell cycle.","evidence":"Domain truncation, EM, siRNA rescue, brefeldin A treatment, cell cycle assays","pmids":["20214750"],"confidence":"High","gaps":["Checkpoint sensor reading Golgi state not identified"]},{"year":2010,"claim":"Pinpointed a PLK1 site within the N-terminal domain adjacent to an internal PDZ ligand whose phosphorylation toggles tethering versus unlinking, defining the structural switch for mitotic unstacking.","evidence":"PLK1 in vitro kinase, phospho-mimetic/alanine mutagenesis, organelle tethering assay","pmids":["20937827"],"confidence":"High","gaps":["Crystallographic basis of the internal-ligand contact not yet shown"]},{"year":2010,"claim":"Demonstrated functional redundancy: only dual GRASP55/GRASP65 depletion collapses the entire stack, refining each GRASP's contribution.","evidence":"siRNA double knockdown, EM, phospho-mutant expression","pmids":["20083603"],"confidence":"High","gaps":["Whether redundancy reflects identical or distinct cisternal contacts unresolved"]},{"year":2010,"claim":"Confirmed caspase-cleaved GRASP65 C-terminal fragments traffic to mitochondria and promote Fas-mediated apoptosis, linking Golgi disassembly to cell-death execution.","evidence":"Caspase-resistant mutants, fractionation, co-IP with Bcl-XL","pmids":["21368855"],"confidence":"Medium","gaps":["Bcl-XL interaction rests on a single Co-IP without reciprocal validation","Pro-death mechanism of fragments not defined"]},{"year":2012,"claim":"Defined the temporal order of mitotic phosphorylation across T220/T224, S277, and S376, with T220/T224 dominant for fragmentation, building a phospho-timing map.","evidence":"Phospho-specific antibodies, in vitro kinase assays, phospho-resistant mutants, immunofluorescence","pmids":["23259055"],"confidence":"High","gaps":["Phosphatases controlling dephosphorylation timing not identified"]},{"year":2013,"claim":"Provided the atomic GRASP-domain dimer structure showing the PDZ2-PDZ2 plus PDZ1-tail-insertion contacts that mediate stacking, explaining the trans-oligomer geometry.","evidence":"X-ray crystallography of GRASP domain, binding assays, mutagenesis","pmids":["23940043"],"confidence":"High","gaps":["Higher-order oligomer assembly on membranes not directly visualized"]},{"year":2014,"claim":"Showed via knockout mice that GRASP65 is dispensable for ribbon morphology and viability but required for cis-cisternal continuity and normal glycosylation, separating structural from functional roles.","evidence":"Knockout mice, FRAP, GSII lectin staining, EM","pmids":["24795147"],"confidence":"High","gaps":["Compensation by GRASP55 in vivo not quantified","Tissue-specific phenotypes not detailed"]},{"year":2015,"claim":"Identified JNK2 as the G2 kinase phosphorylating Ser277 to unlink the ribbon and license mitotic entry, with FRAP showing tubule severing.","evidence":"JNK2 RNAi, JNK inhibitors, FRAP, brefeldin A rescue, cell cycle analysis","pmids":["25948586"],"confidence":"High","gaps":["Upstream activator of JNK2 at the Golgi not identified here"]},{"year":2015,"claim":"Revised the GRASP65-GM130 model structurally, showing GM130 engages both PDZ1 and PDZ2 simultaneously, correcting a PDZ2-only view.","evidence":"1.96 Å crystal structure, mutagenesis, co-IP","pmids":["26363069"],"confidence":"High","gaps":["How GM130 binding coexists with stacking trans-interactions on the same domains unresolved"]},{"year":2015,"claim":"Connected GRASP65 to the actin cytoskeleton via Mena, with actin promoting GRASP65 oligomerization and Golgi fusion.","evidence":"Co-IP, recruitment assay, siRNA, in vitro Golgi fusion","pmids":["26538023"],"confidence":"Medium","gaps":["Mechanism by which actin enhances oligomerization unresolved","Single-lab evidence"]},{"year":2016,"claim":"Showed HCMV exploits GRASP65 phosphorylation-dependent ribbon fragmentation for virion assembly, linking the unstacking pathway to viral pathogenesis.","evidence":"Pharmacological inhibition, infectious yield, virion protein incorporation","pmids":["27703074"],"confidence":"Medium","gaps":["Viral kinase/effector driving GRASP65 phosphorylation not identified","Pharmacological specificity limits mechanism"]},{"year":2017,"claim":"CRISPR double knockout confirmed GRASP55/GRASP65 are required for stacking, controlled trafficking rate, and accurate glycosylation, consolidating the redundancy model with genetic rigor.","evidence":"CRISPR/Cas9 knockout, EM, trafficking and glycosylation assays","pmids":["28814501"],"confidence":"High","gaps":["Direct molecular link between stacking and glycosylation fidelity not defined"]},{"year":2018,"claim":"Identified DjA1 as a direct GRASP65 partner that promotes oligomerization independent of Hsc70 cochaperone activity, adding a positive regulator of stacking.","evidence":"Co-IP, siRNA, in vitro fusion, immunodepletion, purified-protein reconstitution","pmids":["30566031"],"confidence":"High","gaps":["How DjA1 structurally promotes oligomerization unresolved"]},{"year":2019,"claim":"Assigned GRASP65 a role in stabilizing newly nucleated microtubules and Golgi clustering under JNK/ERK phospho-control of S274, broadening function to the cytoskeleton.","evidence":"RNAi, microtubule regrowth assay, tubulin acetylation IF, phospho-mutants","pmids":["31336000"],"confidence":"Medium","gaps":["Direct versus indirect microtubule stabilization mechanism unclear","Single-lab evidence"]},{"year":2021,"claim":"Acute degron depletion showed neither GRASP alone nor both are strictly required to maintain or rebuild stacks, but dual loss strips GM130/p115/Golgin-45 and impairs ribbon linking, refining GRASP65's role toward tethering-protein retention.","evidence":"Degron-tag rapid degradation, EM, tethering-protein immunofluorescence","pmids":["33301566"],"confidence":"High","gaps":["Reconciliation with prior siRNA stacking phenotypes incomplete","What sustains stacking in GRASP absence unknown"]},{"year":2025,"claim":"Established a human Mendelian disease link: GORASP1 loss-of-function causes a neurodevelopmental Golgipathy with hyposialylation and mitotic delay, validating the gene's physiological glycosylation and cell-cycle functions in humans.","evidence":"Patient variant, CRISPR recapitulation in RPE cells, glycosylation and mitosis analysis","pmids":["39933924"],"confidence":"High","gaps":["Mechanistic basis of mitotic delay in patient cells not fully resolved","Genotype-phenotype range from single family"]},{"year":2026,"claim":"Placed PKD2 upstream of GRASP65 S274 phosphorylation and ribbon unlinking, identifying an additional kinase input to the G2/M Golgi switch.","evidence":"Phospho-specific antibody, PKD2 inhibitor and siRNA, Golgi structure and cell cycle assays","pmids":["41892354"],"confidence":"Medium","gaps":["Whether PKD2 acts directly or via JNK2/ERK not resolved","Single-lab, single-paper evidence"]},{"year":null,"claim":"How the structural stacking activity of GRASP65 mechanistically governs glycosylation fidelity and mitotic timing—and how its many kinase inputs are integrated—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking cisternal continuity to glycosylation accuracy","Checkpoint sensor coupling Golgi state to mitotic entry unidentified","Hierarchy among Cdk1, Plk1, ERK, JNK2, and PKD2 inputs not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,4,5,18]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[22,26]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[4,9,15]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,1,9,19]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[3,16]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[9,12,24]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[6,13,20,28]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[9,15,27]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[3,16]}],"complexes":[],"partners":["GM130","PLK1","CDK1","ERK","JNK2","DNAJA1","ENAH","PKD2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BQQ3","full_name":"Golgi reassembly-stacking protein 1","aliases":["Golgi peripheral membrane protein p65","Golgi phosphoprotein 5","GOLPH5","Golgi reassembly-stacking protein of 65 kDa","GRASP65"],"length_aa":440,"mass_kda":46.5,"function":"Key structural protein of the Golgi apparatus (PubMed:33301566). The membrane cisternae of the Golgi apparatus adhere to each other to form stacks, which are aligned side by side to form the Golgi ribbon (PubMed:33301566). Acting in concert with GORASP2/GRASP55, is required for the formation and maintenance of the Golgi ribbon, and may be dispensable for the formation of stacks (PubMed:33301566). However, other studies suggest that GORASP1 plays an important role in assembly and membrane stacking of the cisternae, and in the reassembly of Golgi stacks after breakdown during mitosis (By similarity). Caspase-mediated cleavage of GORASP1 is required for fragmentation of the Golgi during apoptosis (By similarity). Also mediates, via its interaction with GOLGA2/GM130, the docking of transport vesicles with the Golgi membranes (PubMed:16489344). Mediates ER stress-induced unconventional (ER/Golgi-independent) trafficking of core-glycosylated CFTR to cell membrane (PubMed:21884936)","subcellular_location":"Golgi apparatus, cis-Golgi network membrane; Endoplasmic reticulum-Golgi intermediate compartment membrane","url":"https://www.uniprot.org/uniprotkb/Q9BQQ3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GORASP1","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GORASP1","total_profiled":1310},"omim":[{"mim_id":"618638","title":"HECT DOMAIN E3 UBIQUITIN PROTEIN LIGASE 3; HECTD3","url":"https://www.omim.org/entry/618638"},{"mim_id":"606867","title":"GOLGI REASSEMBLY STACKING PROTEIN 1; GORASP1","url":"https://www.omim.org/entry/606867"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GORASP1"},"hgnc":{"alias_symbol":["GRASP65","P65","FLJ23443"],"prev_symbol":["GOLPH5"]},"alphafold":{"accession":"Q9BQQ3","domains":[{"cath_id":"2.30.42.10","chopping":"14-107","consensus_level":"high","plddt":92.3806,"start":14,"end":107},{"cath_id":"2.30.42.10","chopping":"110-194","consensus_level":"high","plddt":92.4482,"start":110,"end":194}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BQQ3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BQQ3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BQQ3-F1-predicted_aligned_error_v6.png","plddt_mean":63.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GORASP1","jax_strain_url":"https://www.jax.org/strain/search?query=GORASP1"},"sequence":{"accession":"Q9BQQ3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BQQ3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BQQ3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BQQ3"}},"corpus_meta":[{"pmid":"9346242","id":"PMC_9346242","title":"GRASP65, 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of GRASP65 organelle tethering involves Polo-like kinase 1 (PLK1) phosphorylation proximate to an internal PDZ ligand.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20937827","citation_count":44,"is_preprint":false},{"pmid":"21368855","id":"PMC_21368855","title":"Caspase cleavage of the Golgi stacking factor GRASP65 is required for Fas/CD95-mediated apoptosis.","date":"2010","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/21368855","citation_count":43,"is_preprint":false},{"pmid":"24795147","id":"PMC_24795147","title":"GRASP65 controls the cis Golgi integrity in vivo.","date":"2014","source":"Biology open","url":"https://pubmed.ncbi.nlm.nih.gov/24795147","citation_count":43,"is_preprint":false},{"pmid":"23940043","id":"PMC_23940043","title":"Structural insight into Golgi membrane stacking by GRASP65 and GRASP55 proteins.","date":"2013","source":"The Journal of biological 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Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/23832210","citation_count":3,"is_preprint":false},{"pmid":"39933924","id":"PMC_39933924","title":"A biallelic variant in GORASP1 causes a novel Golgipathy with glycosylation and mitotic defects.","date":"2025","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/39933924","citation_count":1,"is_preprint":false},{"pmid":"41892354","id":"PMC_41892354","title":"Protein Kinase D2 Regulates GRASP65 Phosphorylation and Golgi Ribbon Unlinking During G2/M Transition.","date":"2026","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/41892354","citation_count":0,"is_preprint":false},{"pmid":"41338296","id":"PMC_41338296","title":"Development and characterization of a membrane-permeant GRASP65-mimetic peptide that inhibits Golgi unlinking and cell cycle progression.","date":"2025","source":"Methods (San Diego, Calif.)","url":"https://pubmed.ncbi.nlm.nih.gov/41338296","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.12.10.627846","title":"GRASP55 Safeguards Proper Lysosome Function by Controlling Sorting of Lysosomal Enzymes at the Golgi","date":"2024-12-12","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.10.627846","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.10.16.618769","title":"GRASP55 Regulates Sorting and Maturation of the Lysosomal Enzyme β-Hexosaminidase A","date":"2024-10-17","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.16.618769","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.06.23.600248","title":"Using Photoswitching FRET to Define the Interaction Boundaries between the Rab1b GTPase and Secretory Cargo","date":"2024-06-24","source":"bioRxiv","url":"https://doi.org/10.1101/2024.06.23.600248","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18975,"output_tokens":7424,"usd":0.084142,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":16695,"output_tokens":7413,"usd":0.1344,"stage2_stop_reason":"end_turn"},"total_usd":0.218542,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"GRASP65 is a 65 kDa Golgi membrane protein whose antibodies and recombinant form block cisternal stacking in a cell-free system; it forms a complex with GM130 and is tightly bound to Golgi membranes even under mitotic conditions when both proteins are heavily phosphorylated, linking it to vesicle docking and cisternal stacking.\",\n      \"method\": \"Cell-free cisternal stacking assay, antibody inhibition, co-immunoprecipitation, biochemical fractionation\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted cell-free stacking assay with antibody/recombinant protein inhibition, replicated across subsequent studies\",\n      \"pmids\": [\"9346242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The binding site for GRASP65 on GM130 maps to the C-terminal sequence xxNDxxxIMVI of GM130, while the binding site for GM130 on GRASP65 maps to amino acids 189–201 (reminiscent of PDZ domains); interaction of the two proteins is required for correct targeting of both to the Golgi apparatus.\",\n      \"method\": \"Gel filtration, in vitro translation, site-directed mutagenesis, immunoprecipitation, GFP-reporter targeting assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis combined with binding assays and functional targeting readout in a single rigorous study\",\n      \"pmids\": [\"9628863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Polo-like kinase (Plk) binds GRASP65 (identified by yeast two-hybrid) and phosphorylates it both in vitro and in vivo; Cdc2 also phosphorylates GRASP65; the conserved C-terminal domain of Plk is required for efficient GRASP65 phosphorylation.\",\n      \"method\": \"Yeast two-hybrid, in vitro kinase assay, in vivo phosphorylation, deletion/frameshift mutant 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 kinase assay plus in vivo evidence, replicated by multiple subsequent studies\",\n      \"pmids\": [\"11050165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"GRASP65 is cleaved specifically by caspase-3 at conserved sites in its C-terminus during apoptosis; expression of a caspase-resistant GRASP65 partially preserved cisternal stacking and inhibited Golgi ribbon breakdown in apoptotic cells.\",\n      \"method\": \"Caspase cleavage assay, expression of caspase-resistant mutants, electron microscopy of Golgi ultrastructure\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro caspase cleavage assay plus mutagenesis rescue experiment with defined structural readout\",\n      \"pmids\": [\"11815631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GRASP65 is the major phosphorylation target of cdc2-cyclin B and polo-like kinases in rat liver Golgi membranes; these kinases alone can unstack Golgi membranes; GRASP65 homodimers on beads form trans-oligomeric aggregates that are disaggregated by mitotic kinases and re-aggregated after dephosphorylation, demonstrating direct mitotically regulated stacking activity.\",\n      \"method\": \"In vitro kinase assay, cell-free Golgi disassembly/reassembly assay, bead aggregation assay, microinjection of anti-GRASP65 antibodies\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal in vitro reconstitution methods plus microinjection in living cells\",\n      \"pmids\": [\"12839990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The N-terminal GRASP domain (aa 1–201) of GRASP65 is necessary and sufficient for dimerization and trans-oligomerization; the C-terminal serine/proline-rich domain (aa 202–446) confers mitotic regulation through phosphorylation sites targeted by cdc2/cyclin B1 and polo-like kinase.\",\n      \"method\": \"Domain deletion/truncation expression, biochemical oligomerization assays, transient overexpression with Golgi fragmentation readout\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic domain mapping with mutagenesis and functional readout in a single study\",\n      \"pmids\": [\"15576368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Cdk1-cyclin B phosphorylates GRASP65 at four C-terminal consensus sites, and phosphorylated GRASP65 recruits the polo box domain of Plk1; mutation of these four sites to alanine abolishes mitotic phosphorylation and Plk1 binding; expression of wild-type but not phosphorylation-defective GRASP65 C-terminus delays mitotic entry.\",\n      \"method\": \"In vitro kinase assay, polo-box domain binding assay, alanine mutagenesis, cell cycle progression assay in NRK cells\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase and binding assays with mutagenesis plus cell-based functional readout\",\n      \"pmids\": [\"15678101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GRASP65 depletion by RNAi causes metaphase arrest with multiple aberrant spindles; the C-terminus of GRASP65 expressed in cells interferes with mitotic entry, revealing a role for GRASP65 in spindle dynamics and cell cycle control beyond Golgi stacking.\",\n      \"method\": \"RNAi depletion in HeLa cells, immunofluorescence microscopy of spindle/centrosome markers, C-terminal construct overexpression\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean RNAi with specific cellular phenotype plus expression construct, but mechanism of spindle effect not fully resolved\",\n      \"pmids\": [\"15888544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GRASP65 is phosphorylated at serine 277 in interphase cells in response to serum/EGF directly by ERK; during mitosis Ser-277 is phosphorylated by Cdk1 instead of ERK; microinjection of a GRASP65 fragment containing Ser-277 inhibits mitosis passage, an effect abolished by S277A mutation.\",\n      \"method\": \"In vitro kinase assay, phospho-specific antibody, microinjection of recombinant protein/peptide fragments, alanine mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assays with phospho-specific antibodies plus functional microinjection rescue experiment\",\n      \"pmids\": [\"15834132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Golgi ribbon formation (lateral cisternal fusion) requires both GM130 and GRASP65; these GM130- and GRASP65-dependent fusion events are necessary for uniform enzyme distribution across the Golgi ribbon.\",\n      \"method\": \"RNAi knockdown, quantitative fluorescence microscopy of Golgi ribbon, enzyme distribution assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — RNAi with multiple functional readouts, replicated in subsequent studies\",\n      \"pmids\": [\"16489344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The yeast GRASP65 orthologue Grh1 associates with the cis-Golgi via an N-terminal amphipathic helix that is N-terminally acetylated; Grh1 forms a complex with the coiled-coil protein Bug1 (Ydl099w); Grh1 interacts with the COPII coat component Sec23/24; genetic interactions with Uso1 and Ypt1 suggest the Grh1-Bug1 complex contributes to COPII vesicle consumption and cis-Golgi formation.\",\n      \"method\": \"Biochemical fractionation, co-immunoprecipitation, genetic interaction analysis, functional assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus genetic epistasis in yeast, single lab\",\n      \"pmids\": [\"17261844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"EGF or LPA stimulation activates ERK, which phosphorylates GRASP65 at serine 277; a S277A or 1–201 truncation mutant (non-phosphorylatable by ERK) prevents Golgi orientation to the leading edge and inhibits centrosome orientation during directed cell migration; ERK phosphorylation of GRASP65 causes loss of GRASP65 oligomerization and Golgi cisternal unstacking.\",\n      \"method\": \"In vitro ERK kinase assay, phospho-specific antibody, expression of phospho-mutants, wound-healing migration assay, brefeldin A rescue\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus multiple functional readouts (migration, oligomerization, stacking) with mutagenesis\",\n      \"pmids\": [\"18762583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GRASP65 PDZ domains directly bind C-terminal valine-bearing cargo receptors (CD8α and Frizzled4); both GRASP65 and GRASP55 are needed sequentially for efficient transport of these receptors to and through the Golgi complex.\",\n      \"method\": \"Direct binding assay (PDZ-cargo interaction), RNAi depletion, protein trafficking assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay plus RNAi trafficking readout, single lab\",\n      \"pmids\": [\"19840934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The first 112 amino acids of GRASP65 (including PDZ1) are sufficient for oligomerization; expression of non-regulatable GRASP65 mutants enhances Golgi stacking in interphase and inhibits fragmentation during mitosis; GRASP65 siRNA reduces cisternae per stack and is rescued by exogenous GRASP65; inhibiting mitotic Golgi disassembly with non-regulatable GRASP65 delayed mitotic entry and suppressed cell growth, an effect rescued by brefeldin A-induced Golgi dispersal.\",\n      \"method\": \"Domain truncation analysis, electron microscopy of Golgi ultrastructure, siRNA depletion with rescue, brefeldin A treatment, cell cycle assays\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — systematic domain analysis, EM readout, siRNA rescue, and functional cell cycle assay in a single study\",\n      \"pmids\": [\"20214750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"GRASP65 links cis-Golgi cisternae via a homotypic N-terminal PDZ interaction; PLK1 phosphorylates a site within the GRASP65 N-terminal domain proximate to an internal PDZ ligand; phospho-mimetic mutation at this site blocks organelle tethering, while alanine substitution prevents mitotic Golgi unlinking; an internal PDZ ligand adjacent to the PLK1 site is required for GRASP65 self-interaction.\",\n      \"method\": \"In vitro PLK1 kinase assay, phospho-mimetic and alanine mutagenesis, organelle tethering assay, interaction assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with mutagenesis directly tested in functional tethering assay\",\n      \"pmids\": [\"20937827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Simultaneous siRNA knockdown of both GRASP55 and GRASP65 leads to disassembly of the entire Golgi stack, whereas depletion of either alone only reduces the number of cisternae per stack; GRASP65 stacks membranes via oligomerization of its N-terminal GRASP domain, regulated by C-terminal phosphorylation.\",\n      \"method\": \"siRNA double knockdown, electron microscopy, phospho-mutant expression\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic siRNA epistasis with EM readout, replicated and extended by subsequent CRISPR studies\",\n      \"pmids\": [\"20083603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Caspase-3 cleavage of GRASP65 during Fas/CD95-mediated apoptosis is required for apoptotic progression; C-terminal caspase-cleavage fragments of GRASP65 are targeted to mitochondria and sensitize cells to Fas ligand; Bcl-XL was identified as a candidate apoptotic binding partner for GRASP65 C-terminal fragments.\",\n      \"method\": \"Caspase-resistant mutant expression, caspase cleavage assays, subcellular fractionation/localization, co-immunoprecipitation with Bcl-XL\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional mutant expression plus localization, but Bcl-XL interaction is a single Co-IP, single lab\",\n      \"pmids\": [\"21368855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GRASP65 is sequentially phosphorylated during mitosis: cdc2 phosphorylates T220/T224, S277, and S376; Plk1 enhances these phosphorylations. T220/T224 is phosphorylated from prophase through anaphase; S277 and S376 from late G2 through telophase; T220A/T224A mutation inhibits mitotic Golgi fragmentation more strongly than S277A or S376A mutations; T220/224 dephosphorylation in cytokinesis precedes S277 but follows S376 dephosphorylation.\",\n      \"method\": \"Phospho-specific antibody generation, in vitro kinase assay, phospho-resistant mutant expression, immunofluorescence microscopy\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — phospho-specific antibodies with in vitro kinase validation and mutant functional assays\",\n      \"pmids\": [\"23259055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of the GRASP65 GRASP domain reveals a dimer in which PDZ2 binding pockets face each other, with the C-terminal tail of one GRASP domain inserting into the PDZ1 pocket of another dimer; both contacts are individually weak but are required in combination for GRASP-mediated Golgi stacking.\",\n      \"method\": \"X-ray crystallography (GRASP65 GRASP domain structure), biochemical binding assays, mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with biochemical validation and mutagenesis in a single study\",\n      \"pmids\": [\"23940043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In GRASP65 knockout mice, the Golgi ribbon appears morphologically normal, but FRAP reveals functional discontinuities in the cis-cisternal membrane network; loss of GRASP65 causes changes in plasma membrane glycosylation (GSII lectin staining) in tissues, demonstrating GRASP65 is required for cis-Golgi network continuity and proper glycosylation but is not essential for organism viability.\",\n      \"method\": \"Homologous recombination knockout, FRAP, GSII lectin staining, electron microscopy\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with FRAP functional assay and biochemical glycosylation readout\",\n      \"pmids\": [\"24795147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"JNK2 phosphorylates GRASP65 at Ser277 during G2, which is essential for separation of Golgi stacks and ribbon unlinking required for mitotic entry; JNK inhibition or JNK2 RNAi causes G2 cell cycle block; this block is bypassed by brefeldin A-induced Golgi dispersal or GRASP65 depletion; JNK2 is required for cleavage of tubules connecting Golgi stacks as measured by FRAP.\",\n      \"method\": \"RNAi knockdown of JNK2, JNK inhibitors, FRAP, brefeldin A rescue, cell cycle analysis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal approaches (RNAi, pharmacological, epistasis) with FRAP functional readout\",\n      \"pmids\": [\"25948586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of GRASP65 PDZ domains in complex with the GM130 C-terminal peptide (1.96 Å) shows that GM130 binds GRASP65 at two distinct sites concurrently, engaging both PDZ1 and PDZ2 domains (contradicting prior models of PDZ2-only interaction); mutagenesis confirms both contacts are required for GRASP65-GM130 association.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with mutagenesis validation in a single rigorous study\",\n      \"pmids\": [\"26363069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The actin elongation factor Mena is a GRASP65-binding protein identified by biochemical methods; Mena is recruited to Golgi membranes through interaction with GRASP65; depletion of Mena or disruption of actin polymerization causes Golgi fragmentation; in vitro, Mena and microfilaments enhance GRASP65 oligomerization and Golgi membrane fusion.\",\n      \"method\": \"Co-immunoprecipitation, Golgi membrane recruitment assay, siRNA depletion, in vitro Golgi fusion assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus in vitro reconstitution and siRNA functional readout, single lab\",\n      \"pmids\": [\"26538023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HCMV-induced Golgi ribbon fragmentation during virion assembly compartment formation is dependent on phosphorylation of GRASP65; inhibition of Golgi membrane fragmentation reduces infectious particle production and alters virion envelope protein incorporation.\",\n      \"method\": \"Pharmacological inhibition of GRASP65 phosphorylation, infectious virus yield assay, virion protein incorporation analysis\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition with two functional readouts (viral yield and envelope protein incorporation), single lab\",\n      \"pmids\": [\"27703074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CRISPR/Cas9 double knockout of GRASP55 and GRASP65 in HeLa and HEK293 cells disperses the Golgi stack into single cisternae and tubulovesicular structures, accelerates protein trafficking, and impairs accurate glycosylation of proteins and lipids.\",\n      \"method\": \"CRISPR/Cas9 knockout, electron microscopy, protein trafficking assays, glycosylation analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR knockout with EM and multiple biochemical functional readouts, extends and confirms prior siRNA work\",\n      \"pmids\": [\"28814501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DjA1 (DnaJ homolog subfamily A member 1) is a GRASP65-binding protein; depletion of DjA1 causes Golgi fragmentation and delayed Golgi reassembly; immunodepletion of DjA1 from interphase cytosol reduces GRASP65 oligomerization and Golgi membrane fusion in vitro; DjA1 promotes GRASP65 oligomerization through direct interaction independent of its Hsc70 cochaperone activity.\",\n      \"method\": \"Co-immunoprecipitation, siRNA depletion, in vitro Golgi fusion assay, immunodepletion, purified protein reconstitution\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro reconstitution with purified proteins plus immunodepletion and cell-based rescue\",\n      \"pmids\": [\"30566031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GRASP65 is required for stabilization of newly nucleated microtubules (leading to their acetylation) and clustering of Golgi stacks; GRASP65 is not involved in microtubule nucleation or anchoring; ribbon formation and microtubule stabilization are both regulated by JNK/ERK-mediated phosphorylation of GRASP65 S274 (human); tubulin acetylation is reduced during G2 as phosphorylation of GRASP65 increases.\",\n      \"method\": \"RNAi depletion, microtubule regrowth assay, tubulin acetylation immunofluorescence, phospho-mutant expression\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi with multiple mechanistic readouts and phospho-mutant rescue, single lab\",\n      \"pmids\": [\"31336000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Acute depletion of GRASP65 alone (via degron-tag) does not affect the Golgi ribbon; chronic degradation of GRASP65 does not disrupt ribbon connectivity; acute double depletion of both GRASP55 and GRASP65 causes loss of vesicle tethering proteins GM130, p115, and Golgin-45 from the Golgi and compromises ribbon linking; neither GRASP alone nor both together are required for maintaining stacks or de novo assembly of stacked cisternae after mitosis.\",\n      \"method\": \"Degron-tag rapid protein degradation, electron microscopy, immunofluorescence for tethering proteins\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — acute degron-mediated depletion (more rigorous than RNAi) with EM and protein localization readouts, contradicts some prior siRNA work\",\n      \"pmids\": [\"33301566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A human loss-of-function variant in GORASP1 (c.1170_1171del; p.Asp390Glufs*18) causes complete absence of GRASP65 protein and results in a neurodevelopmental Golgipathy; patient cells and CRISPR-engineered RPE cells show hyposialylation (glycosylation defects) and mitotic delay (excess prometaphase/metaphase with polar chromosomes) without Golgi fragmentation.\",\n      \"method\": \"Patient variant identification, CRISPR/Cas9 recapitulation in RPE cells, glycosylation analysis (hyposialylation), cell cycle/mitosis analysis\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human loss-of-function combined with CRISPR recapitulation in cell model with multiple orthogonal functional readouts\",\n      \"pmids\": [\"39933924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Protein kinase D2 (PKD2) is an upstream regulator required for GRASP65 phosphorylation at S274 (human) and Golgi ribbon unlinking; PKD2 inhibition or depletion reduces GRASP65-S274 phosphorylation, decreases Golgi unlinking, and delays G2/M transition; PKD2-activating stimuli (phorbol esters, nocodazole) enhance GRASP65 phosphorylation in a PKD2-dependent manner.\",\n      \"method\": \"Phospho-specific antibody generation, PKD2 inhibitor treatment, siRNA depletion of PKD2, Golgi structure analysis, cell cycle assay\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and genetic PKD2 inhibition with functional GRASP65 phosphorylation and cell cycle readouts, single lab, single paper\",\n      \"pmids\": [\"41892354\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GRASP65 (GORASP1) is a peripheral cis-Golgi membrane protein that dimerizes and forms trans-oligomers through its N-terminal tandem PDZ (GRASP) domain to physically tether adjacent Golgi cisternae into stacks and link stacks into the Golgi ribbon; it constitutively binds GM130 (via PDZ1/PDZ2 contacts with the GM130 C-terminus) to support vesicle tethering and Golgi targeting; during mitosis, sequential phosphorylation by Cdk1-cyclin B and Plk1 (with PLK1 acting directly on the N-terminal PDZ interaction surface) dissolves GRASP65 oligomers to drive Golgi ribbon unlinking and cisternal unstacking, a process also regulated by ERK/JNK2 phosphorylation of Ser277/S274 upstream of a PKD2-JNK2 signaling axis; caspase-3 cleaves GRASP65 during apoptosis releasing C-terminal mitochondria-targeted fragments that promote cell death; GRASP65 additionally stabilizes newly nucleated microtubules, facilitates transport of C-terminal valine-bearing cargoes through its PDZ domains, and is required for cis-Golgi network continuity and proper glycosylation, with human loss-of-function causing a Golgipathy marked by hyposialylation and mitotic delay.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GORASP1 (GRASP65) is a peripheral cis-Golgi membrane protein that physically tethers and stacks Golgi cisternae and is integrated into mitotic cell-cycle control of Golgi architecture [#0, #4]. Its N-terminal GRASP domain (PDZ1/PDZ2) is necessary and sufficient for dimerization and trans-oligomerization, the activity that holds adjacent cisternae together [#5, #13], with a crystallographically defined dimer in which one GRASP domain's C-terminal tail inserts into the PDZ1 pocket of an adjacent dimer—two individually weak contacts that together drive stacking [#18]. Through these PDZ domains GRASP65 constitutively binds the C-terminal tail of GM130 at two concurrent sites engaging both PDZ1 and PDZ2, an interaction required for correct Golgi targeting of both proteins and for vesicle tethering [#1, #21]. GRASP65 together with GM130 mediates lateral cisternal fusion to build the Golgi ribbon and ensure uniform glycosylation enzyme distribution [#9], and it acts redundantly with GRASP55: loss of both, but not either alone, disperses the stack and impairs accurate protein and lipid glycosylation [#15, #24]. Oligomerization is dissolved during mitosis by sequential C-terminal phosphorylation: Cdk1-cyclin B phosphorylates multiple consensus sites and recruits the Plk1 polo-box domain, while PLK1 also acts at an N-terminal site adjacent to an internal PDZ ligand to disrupt self-interaction and unlink the ribbon [#6, #14, #17]; an ERK/JNK2-targeted Ser277/S274 site, downstream of a PKD2 signaling axis, drives interphase and G2 unstacking that governs Golgi orientation during migration and timely mitotic entry [#8, #11, #20, #29]. During apoptosis caspase-3 cleaves the C-terminus, releasing mitochondria-targeted fragments that promote cell death [#3, #16]. GRASP65 additionally facilitates PDZ-dependent transport of C-terminal valine-bearing cargoes [#12] and stabilizes newly nucleated microtubules [#26]. Human loss-of-function (p.Asp390Glufs*18, absent protein) causes a neurodevelopmental Golgipathy characterized by hyposialylation and mitotic delay without Golgi fragmentation [#28].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established GRASP65 as a Golgi membrane protein with direct stacking activity, answering whether a defined factor controls cisternal stacking.\",\n      \"evidence\": \"Cell-free cisternal stacking assay with antibody/recombinant inhibition and co-IP with GM130\",\n      \"pmids\": [\"9346242\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of stacking activity not yet resolved\", \"Phosphoregulation defined only as bulk mitotic phosphorylation\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Mapped the reciprocal GRASP65-GM130 binding sites and showed the interaction targets both proteins to the Golgi, defining the first molecular partner contact.\",\n      \"evidence\": \"Gel filtration, in vitro translation, site-directed mutagenesis, GFP-reporter targeting\",\n      \"pmids\": [\"9628863\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single-site model later revised by structural work\", \"Did not establish stoichiometry or affinity\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified Plk and Cdc2 as the kinases acting on GRASP65, linking it to mitotic kinase cascades.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro and in vivo kinase assays, Plk deletion mutants\",\n      \"pmids\": [\"11050165\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phosphosites not yet mapped\", \"Functional consequence on stacking not directly tested here\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Showed caspase-3 cleaves GRASP65 during apoptosis to drive Golgi breakdown, connecting it to programmed cell death.\",\n      \"evidence\": \"Caspase cleavage assays, caspase-resistant mutant expression, Golgi EM\",\n      \"pmids\": [\"11815631\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Fate and function of cleavage fragments not yet defined\", \"Physiological apoptotic trigger not specified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated directly that mitotic kinases disaggregate GRASP65 trans-oligomers and dephosphorylation re-aggregates them, establishing phospho-regulated oligomerization as the stacking switch.\",\n      \"evidence\": \"Bead aggregation assay, cell-free Golgi disassembly/reassembly, microinjection of anti-GRASP65 antibody\",\n      \"pmids\": [\"12839990\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural geometry of trans-oligomer unknown\", \"Individual phosphosite contributions unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Separated GRASP65 into an N-terminal oligomerization module and a C-terminal phosphoregulatory module, defining domain architecture.\",\n      \"evidence\": \"Domain deletion/truncation with oligomerization and Golgi fragmentation readouts\",\n      \"pmids\": [\"15576368\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic structure of GRASP domain not yet available\", \"C-terminal phosphosite identities incomplete\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined the Cdk1-cyclin B four-site phosphorylation that creates the Plk1 polo-box docking platform and gates mitotic entry, establishing the priming-kinase mechanism.\",\n      \"evidence\": \"In vitro kinase and polo-box binding assays, alanine mutagenesis, cell cycle progression in NRK cells\",\n      \"pmids\": [\"15678101\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Golgi unstacking signals back to mitotic entry not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Revealed a GRASP65 requirement for spindle integrity and cell cycle control beyond Golgi stacking.\",\n      \"evidence\": \"RNAi depletion in HeLa cells, spindle/centrosome immunofluorescence, C-terminal overexpression\",\n      \"pmids\": [\"15888544\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting GRASP65 to spindle dynamics not resolved\", \"Indirect effect via Golgi-mitosis checkpoint not excluded\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed Ser277 is an ERK target in interphase but a Cdk1 target in mitosis, identifying a signal-integrating phosphosite.\",\n      \"evidence\": \"In vitro kinase assays, phospho-specific antibody, microinjection of fragments, S277A mutagenesis\",\n      \"pmids\": [\"15834132\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effector of Ser277 phosphorylation not defined here\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that GM130 and GRASP65 jointly mediate lateral cisternal fusion required for ribbon formation and uniform enzyme distribution.\",\n      \"evidence\": \"RNAi knockdown, quantitative Golgi ribbon imaging, enzyme distribution assays\",\n      \"pmids\": [\"16489344\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Fusion machinery downstream of tethering not identified\", \"Glycosylation consequences not directly measured\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed the yeast orthologue Grh1 acts at COPII-to-cis-Golgi traffic via Bug1 and Sec23/24, placing GRASP function in early secretory pathway biogenesis.\",\n      \"evidence\": \"Fractionation, reciprocal co-IP, genetic interaction analysis in yeast\",\n      \"pmids\": [\"17261844\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conservation of COPII-coupling role in mammalian GRASP65 not tested\", \"Single-lab yeast genetics\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linked EGF/LPA-ERK phosphorylation of Ser277 to GRASP65 de-oligomerization and Golgi reorientation during directed cell migration, extending function to interphase polarity.\",\n      \"evidence\": \"ERK kinase assay, phospho-mutants, wound-healing migration, brefeldin A rescue\",\n      \"pmids\": [\"18762583\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Golgi unstacking promotes centrosome/Golgi orientation mechanistically unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identified PDZ-dependent binding of C-terminal valine cargo receptors, assigning GRASP65 a direct cargo-transport role.\",\n      \"evidence\": \"Direct PDZ-cargo binding assay, RNAi depletion, trafficking assays\",\n      \"pmids\": [\"19840934\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality of valine-motif cargo selection not established\", \"Single-lab evidence\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved that non-regulatable GRASP65 enhances stacking and blocks mitotic fragmentation, and that Golgi disassembly is needed for timely mitotic entry, tying organelle inheritance to cell cycle.\",\n      \"evidence\": \"Domain truncation, EM, siRNA rescue, brefeldin A treatment, cell cycle assays\",\n      \"pmids\": [\"20214750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Checkpoint sensor reading Golgi state not identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Pinpointed a PLK1 site within the N-terminal domain adjacent to an internal PDZ ligand whose phosphorylation toggles tethering versus unlinking, defining the structural switch for mitotic unstacking.\",\n      \"evidence\": \"PLK1 in vitro kinase, phospho-mimetic/alanine mutagenesis, organelle tethering assay\",\n      \"pmids\": [\"20937827\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystallographic basis of the internal-ligand contact not yet shown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated functional redundancy: only dual GRASP55/GRASP65 depletion collapses the entire stack, refining each GRASP's contribution.\",\n      \"evidence\": \"siRNA double knockdown, EM, phospho-mutant expression\",\n      \"pmids\": [\"20083603\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether redundancy reflects identical or distinct cisternal contacts unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Confirmed caspase-cleaved GRASP65 C-terminal fragments traffic to mitochondria and promote Fas-mediated apoptosis, linking Golgi disassembly to cell-death execution.\",\n      \"evidence\": \"Caspase-resistant mutants, fractionation, co-IP with Bcl-XL\",\n      \"pmids\": [\"21368855\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Bcl-XL interaction rests on a single Co-IP without reciprocal validation\", \"Pro-death mechanism of fragments not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the temporal order of mitotic phosphorylation across T220/T224, S277, and S376, with T220/T224 dominant for fragmentation, building a phospho-timing map.\",\n      \"evidence\": \"Phospho-specific antibodies, in vitro kinase assays, phospho-resistant mutants, immunofluorescence\",\n      \"pmids\": [\"23259055\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatases controlling dephosphorylation timing not identified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Provided the atomic GRASP-domain dimer structure showing the PDZ2-PDZ2 plus PDZ1-tail-insertion contacts that mediate stacking, explaining the trans-oligomer geometry.\",\n      \"evidence\": \"X-ray crystallography of GRASP domain, binding assays, mutagenesis\",\n      \"pmids\": [\"23940043\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Higher-order oligomer assembly on membranes not directly visualized\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed via knockout mice that GRASP65 is dispensable for ribbon morphology and viability but required for cis-cisternal continuity and normal glycosylation, separating structural from functional roles.\",\n      \"evidence\": \"Knockout mice, FRAP, GSII lectin staining, EM\",\n      \"pmids\": [\"24795147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensation by GRASP55 in vivo not quantified\", \"Tissue-specific phenotypes not detailed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified JNK2 as the G2 kinase phosphorylating Ser277 to unlink the ribbon and license mitotic entry, with FRAP showing tubule severing.\",\n      \"evidence\": \"JNK2 RNAi, JNK inhibitors, FRAP, brefeldin A rescue, cell cycle analysis\",\n      \"pmids\": [\"25948586\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream activator of JNK2 at the Golgi not identified here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Revised the GRASP65-GM130 model structurally, showing GM130 engages both PDZ1 and PDZ2 simultaneously, correcting a PDZ2-only view.\",\n      \"evidence\": \"1.96 Å crystal structure, mutagenesis, co-IP\",\n      \"pmids\": [\"26363069\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How GM130 binding coexists with stacking trans-interactions on the same domains unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected GRASP65 to the actin cytoskeleton via Mena, with actin promoting GRASP65 oligomerization and Golgi fusion.\",\n      \"evidence\": \"Co-IP, recruitment assay, siRNA, in vitro Golgi fusion\",\n      \"pmids\": [\"26538023\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which actin enhances oligomerization unresolved\", \"Single-lab evidence\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed HCMV exploits GRASP65 phosphorylation-dependent ribbon fragmentation for virion assembly, linking the unstacking pathway to viral pathogenesis.\",\n      \"evidence\": \"Pharmacological inhibition, infectious yield, virion protein incorporation\",\n      \"pmids\": [\"27703074\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Viral kinase/effector driving GRASP65 phosphorylation not identified\", \"Pharmacological specificity limits mechanism\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"CRISPR double knockout confirmed GRASP55/GRASP65 are required for stacking, controlled trafficking rate, and accurate glycosylation, consolidating the redundancy model with genetic rigor.\",\n      \"evidence\": \"CRISPR/Cas9 knockout, EM, trafficking and glycosylation assays\",\n      \"pmids\": [\"28814501\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular link between stacking and glycosylation fidelity not defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified DjA1 as a direct GRASP65 partner that promotes oligomerization independent of Hsc70 cochaperone activity, adding a positive regulator of stacking.\",\n      \"evidence\": \"Co-IP, siRNA, in vitro fusion, immunodepletion, purified-protein reconstitution\",\n      \"pmids\": [\"30566031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DjA1 structurally promotes oligomerization unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Assigned GRASP65 a role in stabilizing newly nucleated microtubules and Golgi clustering under JNK/ERK phospho-control of S274, broadening function to the cytoskeleton.\",\n      \"evidence\": \"RNAi, microtubule regrowth assay, tubulin acetylation IF, phospho-mutants\",\n      \"pmids\": [\"31336000\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect microtubule stabilization mechanism unclear\", \"Single-lab evidence\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Acute degron depletion showed neither GRASP alone nor both are strictly required to maintain or rebuild stacks, but dual loss strips GM130/p115/Golgin-45 and impairs ribbon linking, refining GRASP65's role toward tethering-protein retention.\",\n      \"evidence\": \"Degron-tag rapid degradation, EM, tethering-protein immunofluorescence\",\n      \"pmids\": [\"33301566\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciliation with prior siRNA stacking phenotypes incomplete\", \"What sustains stacking in GRASP absence unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established a human Mendelian disease link: GORASP1 loss-of-function causes a neurodevelopmental Golgipathy with hyposialylation and mitotic delay, validating the gene's physiological glycosylation and cell-cycle functions in humans.\",\n      \"evidence\": \"Patient variant, CRISPR recapitulation in RPE cells, glycosylation and mitosis analysis\",\n      \"pmids\": [\"39933924\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic basis of mitotic delay in patient cells not fully resolved\", \"Genotype-phenotype range from single family\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Placed PKD2 upstream of GRASP65 S274 phosphorylation and ribbon unlinking, identifying an additional kinase input to the G2/M Golgi switch.\",\n      \"evidence\": \"Phospho-specific antibody, PKD2 inhibitor and siRNA, Golgi structure and cell cycle assays\",\n      \"pmids\": [\"41892354\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PKD2 acts directly or via JNK2/ERK not resolved\", \"Single-lab, single-paper evidence\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the structural stacking activity of GRASP65 mechanistically governs glycosylation fidelity and mitotic timing—and how its many kinase inputs are integrated—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking cisternal continuity to glycosylation accuracy\", \"Checkpoint sensor coupling Golgi state to mitotic entry unidentified\", \"Hierarchy among Cdk1, Plk1, ERK, JNK2, and PKD2 inputs not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 4, 5, 18]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [22, 26]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [4, 9, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1, 9, 19]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [3, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [9, 12, 24]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [6, 13, 20, 28]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [9, 15, 27]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 16]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GM130\", \"PLK1\", \"CDK1\", \"ERK\", \"JNK2\", \"DNAJA1\", \"ENAH\", \"PKD2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}