{"gene":"RABEP1","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1995,"finding":"Rabaptin-5 (RABEP1) is a direct effector of GTP-bound Rab5 that is required for early endosome membrane docking and fusion. It is mainly cytosolic but colocalizes with Rab5 on early endosomes; Rab5 recruits it to purified early endosomes in a GTP-dependent manner, and immunodepletion of rabaptin-5 from cytosol strongly inhibits Rab5-dependent early endosome fusion.","method":"Co-immunoprecipitation, immunodepletion from cytosol, in vitro endosome fusion assay with purified early endosomes, overexpression with morphological readout (endosome enlargement)","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro reconstitution (endosome fusion assay), immunodepletion rescue, GTP-dependent recruitment to purified organelles; foundational paper replicated extensively","pmids":["8521472"],"is_preprint":false},{"year":1997,"finding":"Rabaptin-5 forms a tight physical complex with Rabex-5, a novel 60 kDa Rab5 GDP/GTP exchange factor homologous to yeast Vps9p. This complex is essential for endocytic membrane fusion; Rabex-5 displays GDP/GTP exchange activity on Rab5 upon membrane delivery, and the complex stabilizes Rab5 in the GTP-active state.","method":"Nanoelectrospray mass spectrometry identification, biochemical co-purification, in vitro nucleotide exchange assay, cell-free endosome fusion assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro GEF assay, reconstitution of complex, fusion assay; independently replicated","pmids":["9323142"],"is_preprint":false},{"year":1997,"finding":"Rabaptin-5 is cleaved by caspase-family proteases during apoptosis, and this selective cleavage is responsible for the block in endosome fusion observed in apoptotic cells. Cleavage was shown in a cell-free Xenopus egg-extract apoptosis system and in cellular apoptosis models; Bcl-2/Bcl-xL or caspase inhibitors prevented both cleavage and fusion inhibition.","method":"Cell-free Xenopus egg-extract apoptosis system, immunoblot detection of cleavage, caspase inhibitors, Bcl-2/Bcl-xL rescue, endosome fusion assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reconstituted cell-free system with inhibitor rescue and multiple cellular models; published in high-impact journal with orthogonal approaches","pmids":["9321397"],"is_preprint":false},{"year":1998,"finding":"Rabaptin-5 contains two distinct Rab-binding domains: a 73-residue C-terminal region necessary and sufficient for interaction with GTP-bound Rab5 and Rab5-dependent recruitment to early endosomes, and an N-terminal domain that mediates direct interaction with GTP-bound Rab4. Native cytosolic Rabaptin-5 exists as a homodimer dependent on its coiled-coil sequences.","method":"Deletion mutagenesis, GST pulldown assays, yeast two-hybrid, immunofluorescence colocalization, gel filtration (native complex analysis)","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple deletion mutants, in vitro binding assays, and localization studies; replicated by subsequent isoform studies","pmids":["9524117"],"is_preprint":false},{"year":1998,"finding":"Rabaptin-5 interacts with the neuronal growth-associated protein GAP-43 in a Ca2+-dependent manner, and this interaction modulates endocytosis and synaptic vesicle recycling in neurons.","method":"Yeast two-hybrid, co-immunoprecipitation, endocytosis assays in neuronal cells, overexpression studies","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — yeast two-hybrid plus co-IP plus functional endocytosis assay, single lab","pmids":["9742146"],"is_preprint":false},{"year":2001,"finding":"When physically associated in a complex, Rabaptin-5 increases the nucleotide exchange activity of Rabex-5 on Rab5. Rab5-dependent recruitment of Rabaptin-5 to early endosomes is completely dependent on its physical association with Rabex-5, and complex formation is essential for early endosome homotypic fusion.","method":"Reconstitution with recombinant proteins, in vitro GEF assay, endosome recruitment assay, cell-free endosome fusion assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — fully reconstituted with recombinant proteins, multiple orthogonal assays (GEF, recruitment, fusion)","pmids":["11452015"],"is_preprint":false},{"year":2001,"finding":"Rabaptin-5 interacts with Rab33b (a Golgi-specific Rab) in its GTP-bound form, suggesting Rabaptin-5 functions not only in the endocytic pathway but also at the Golgi. The interaction was demonstrated by GST-Rab33b pulldown with detection by Western blot and mass spectrometry.","method":"GST-Rab33b (GTP-locked) pulldown, Western blot, mass spectrometry","journal":"FEBS letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single pulldown assay, no functional follow-up for Rabaptin-5 specifically at the Golgi","pmids":["11718716"],"is_preprint":false},{"year":2001,"finding":"Rabphilin dissociated from Rab3 promotes endocytosis through direct interaction with Rabaptin-5. The Rabphilin V61A mutant (unable to bind Rab3) interacts with Rabaptin-5 and enhances transferrin internalization, whereas Rabphilin L83A fails to bind Rabaptin-5 and does not stimulate endocytosis.","method":"Co-immunoprecipitation, transferrin endocytosis assay, point-mutant analysis, overexpression in secretory cells","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — reciprocal binding data with point mutants, functional endocytosis readout; single lab","pmids":["11309205"],"is_preprint":false},{"year":2002,"finding":"Gamma1-adaptin (a subunit of the AP-1 clathrin adaptor complex at the TGN) directly interacts with Rabaptin-5 through its ear domain binding to the C-terminal coiled-coil region of Rabaptin-5. The two proteins colocalize on perinuclear structures (recycling endosomes) and redistribute to cytoplasm upon brefeldin A treatment.","method":"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, immunofluorescence colocalization","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — in vitro and in vivo binding confirmed by two methods plus localization; single lab","pmids":["11872161"],"is_preprint":false},{"year":2003,"finding":"GGAs (Arf-dependent clathrin adaptors) interact with the Rabaptin-5-Rabex-5 complex via a bipartite mechanism: GGA-GAE domains recognize the FGPLV sequence (residues 439-443) in Rabaptin-5 (also recognized by gamma1- and gamma2-adaptin ears), while GGA-GAT domains bind the C-terminal coiled-coils of Rabaptin-5. GFP-Rabaptin-5 overexpression shifts GGA1 and associated cargo to enlarged early endosomes.","method":"Co-immunoprecipitation, GST pulldown, site-directed mutagenesis of FGPLV motif, immunofluorescence relocalization assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (pulldown, co-IP, mutagenesis, functional localization shift); replicated in part by GGA1 GAT domain crystal structure studies","pmids":["12505986"],"is_preprint":false},{"year":2003,"finding":"The GGA1 GAT domain binds Rabaptin-5 through a hydrophobic surface patch on its C-terminal three-helix bundle. The N284S mutation in this patch reduces Rabaptin-5 binding, and the reciprocal S293N mutation in GGA3 partially confers Rabaptin-5 binding; binding of GAT to Rabaptin-5 is independent of its interaction with ARF.","method":"Crystal structure of GGA1 GAT domain, site-directed mutagenesis, in vitro binding assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus mutagenesis and in vitro binding; single lab but multiple orthogonal methods","pmids":["14636058"],"is_preprint":false},{"year":2004,"finding":"Rabaptin-5/Rabex-5 complex negatively regulates AP-1/clathrin-coated vesicle formation from endosomes in a Rab4-dependent recycling pathway. Depletion of rabaptin-5/rabex-5 from cytosol stimulated recycling vesicle production, while addition of purified protein strongly inhibited it; Rab4, but not Rab5, was required for this process.","method":"In vitro vesicle formation assay using surface-biotinylated receptor, immunodepletion from cytosol, add-back of purified protein, brefeldin A inhibition","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted vesicle formation assay with immunodepletion and add-back; multiple inhibitor controls; single lab","pmids":["15331762"],"is_preprint":false},{"year":2005,"finding":"The Rabaptin-5δ isoform interacts with GTP-bound Rab5 but not with Rab4, unlike full-length Rabaptin-5 which binds both. This is due to a disrupted Rab4 binding site caused by the alternative splicing deletion, confirmed by yeast two-hybrid, GST pulldown, and immunofluorescence colocalization.","method":"Yeast two-hybrid, GST pulldown, immunofluorescence colocalization in BHK-21 cells","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — two orthogonal binding assays plus localization; single lab","pmids":["15634330"],"is_preprint":false},{"year":2006,"finding":"Rabaptin-5 exists as a dimer in cells, and its δ and γ isoforms also form dimers, providing the first direct evidence for Rabaptin-5 dimerization in a cellular context. Dimerization was established using biochemical cross-linking and co-immunoprecipitation approaches.","method":"Co-immunoprecipitation, cross-linking, biochemical fractionation","journal":"Biochemistry. Biokhimiia","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, limited methodological detail in abstract","pmids":["17223781"],"is_preprint":false},{"year":2006,"finding":"Rabaptin-5γ and Rabaptin-5δ isoforms are cleaved by caspase-3-related proteases in apoptotic cell extracts, and both contain an N-terminal Rab5 binding site that becomes physically separated from the C-terminal Rab5 binding site after apoptotic cleavage, providing a mechanistic model for inactivation of endosome fusion.","method":"In vitro cleavage by caspase-3 in cell extracts, immunoblot detection of cleavage products, mapping of Rab5 binding sites on deletion mutants","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — cell extract cleavage assay plus domain mapping; single lab, builds on prior work","pmids":["16861912"],"is_preprint":false},{"year":2007,"finding":"Rabex-5 can target to early endosomes and activate Rab5 in vivo via an early endosomal targeting (EET) domain (residues 81-230) that is independent of its Rabaptin-5-binding domain; Rabaptin-5 is therefore not required for Rabex-5 membrane targeting and Rab5 activation in vivo, despite being required in vitro.","method":"Deletion mutagenesis of Rabex-5, fluorescence microscopy of GFP-tagged constructs, Rab5-GTP activation assays in cells","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic mutagenesis with cellular localization and Rab5 activation readouts; single lab, challenges prior model","pmids":["17699593"],"is_preprint":false},{"year":2008,"finding":"In mast cells, Rabaptin-5 knockdown reduces surface expression of FcεRI and β1 integrin (by diminishing receptor surface stability) but does not impair FcεRI internalization or endosome fusion. This receptor surface stabilization function of Rabaptin-5 reduces mast cell sensitivity to antigen-induced mediator release and Ag-induced adhesion/migration.","method":"shRNA knockdown, flow cytometry for surface receptor levels, transferrin endocytosis assay, mediator release assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — shRNA knockdown with multiple orthogonal functional readouts; single lab","pmids":["18698003"],"is_preprint":false},{"year":2010,"finding":"The Rabex-5/Rabaptin-5 complex forms a positive feedback loop for Rab5 activation on endosomal membranes: Rabaptin-5 binding to Rab5-GTP recruits the Rabex-5/Rabaptin-5 complex to the membrane, where Rabex-5 generates more Rab5-GTP. This indirect pathway has a delayed onset ('delayed response') requiring above-endogenous levels of Rab5 or Rabex-5 to engage.","method":"Mathematical modeling, kinetic analysis of Rab5 activation in cells with varying Rabex-5 expression levels, fluorescence assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — kinetic cell-based measurements integrated with mathematical model; single lab","pmids":["20169068"],"is_preprint":false},{"year":2012,"finding":"Protein kinase D (PKD) phosphorylates Rabaptin-5 at Ser407, and this phosphorylation is necessary and sufficient for PDGF-dependent short-loop recycling of αvβ3 integrin. Phosphorylated Rabaptin-5 interacts preferentially with Rab4 (not Rab5) near the front of migrating cells to deliver αvβ3 to the leading edge, driving persistent cell migration and invasion, while also inhibiting α5β1 recycling.","method":"In vitro kinase assay (PKD phosphorylation of Rabaptin-5), phospho-specific antibodies, site-directed mutagenesis (S407A/S407D), co-immunoprecipitation with Rab4/Rab5, integrin recycling assays, 2D migration and invasion assays","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro kinase assay, phospho-mutagenesis with gain/loss-of-function, multiple functional readouts (recycling, migration, invasion); single lab but multiple orthogonal methods","pmids":["22975325"],"is_preprint":false},{"year":2012,"finding":"KV10.1 potassium channel physically interacts with Rabaptin-5 and colocalizes on large early endosomes induced by Rab5 hyperactivity. Silencing Rabaptin-5 reduces recycling of KV10.1 to the cell surface and decreases KV10.1 current density in cells natively expressing the channel.","method":"Co-immunoprecipitation, immunofluorescence colocalization, siRNA knockdown, whole-cell patch-clamp recording","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — co-IP plus functional knockdown with electrophysiology readout; single lab","pmids":["22841712"],"is_preprint":false},{"year":2013,"finding":"In Drosophila, Rabaptin-5 functions as a neoplastic tumor suppressor; loss-of-function mutants cause epithelial disruption and over-proliferation associated with upregulation of JNK and JAK/STAT signaling, without disruption of apico-basal polarity. Its ability to bind Rab5, modulate early endosomal dynamics, and interact with Rabex-5 is conserved in Drosophila.","method":"Genetic mosaic analysis in Drosophila (loss-of-function mutations), epistasis with JNK/JAK-STAT pathway reporters, Rab5 binding assays","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in Drosophila with signaling pathway readouts; conserved protein, single study","pmids":["24104056"],"is_preprint":false},{"year":2014,"finding":"Rabep1 couples the polycystin complex (PC1/PC2) to a GGA1/Arl3-based ciliary trafficking module at the TGN, enabling ciliary targeting of these large transmembrane proteins. This was identified by yeast two-hybrid screening and validated with a candidate approach.","method":"Yeast two-hybrid screening, co-immunoprecipitation, candidate interaction validation, knockdown with ciliary localization readout","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — yeast two-hybrid plus co-IP and functional ciliary targeting assay; single lab","pmids":["25405894"],"is_preprint":false},{"year":2014,"finding":"The Rabaptin-5γ isoform, despite its ability to interact with Rab5, is absent from early endosomes and is instead localized to the trans-Golgi network and a Rab4-positive compartment, indicating it functions in membrane transport steps other than Rab5-driven early endosome fusion.","method":"Immunofluorescence microscopy, subcellular fractionation, Rab5/Rab4 co-localization analysis in transfected cells","journal":"Biochemistry. Biokhimiia","confidence":"Low","confidence_rationale":"Tier 3 / Weak — localization data without mechanistic functional follow-up; single lab","pmids":["25385014"],"is_preprint":false},{"year":2014,"finding":"HDAC6 overexpression in gastric cancer inhibits rabaptin-5-mediated early endosome fusion, thereby prolonging EGFR activation and sustaining growth stimulation. HDAC6 knockdown caused inhibition of gastric cancer cell growth associated with decreased EGFR signaling.","method":"HDAC6 shRNA knockdown, EGFR signaling assays, endosome fusion assays, cell growth assays","journal":"Cancer letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — abstract does not detail direct mechanistic link between HDAC6 and Rabaptin-5; limited methodological detail about the Rabaptin-5-specific mechanism","pmids":["25111897"],"is_preprint":false},{"year":2015,"finding":"ITSN2L (Intersectin-2Long) interacts with Rabaptin-5 (RABEP1) via its CC domain binding to the CC3 region of RABEP1. ITSN2L overexpression promotes RABEP1 degradation and represses RABEP1-enhanced endosome aggregation, functioning as a negative regulator of RABEP1 in endocytosis.","method":"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, colocalization microscopy, overexpression with endosome morphology readout","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — yeast two-hybrid plus GST pulldown plus co-IP, functional endosome assay; single lab","pmids":["26633357"],"is_preprint":false},{"year":2021,"finding":"HD-PTP (PTPN23) binds directly to Rabaptin-5 between its Rabex-5- and Rab5-binding domains, at the same site that interacts with ESCRT-0/ESCRT-III. HD-PTP depletion leads to Rabaptin-5-dependent hyperactivation of Rab5 and accumulation of hyperphosphorylated Rabaptin-5, blocking cargo exit from Rab5-rich endosomes. This indicates HD-PTP coordinates MVB sorting with endosomal maturation by modulating Rabex-5-Rabaptin-5 activity.","method":"Co-immunoprecipitation (direct binding), siRNA depletion of HD-PTP, phosphorylation analysis of Rabaptin-5, Rab5-GTP activation assay, ESCRT-III peptide competition binding assay","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding mapped to defined domains, competition assay, functional knockdown with Rab5 activation readout; single lab, multiple orthogonal methods","pmids":["34657963"],"is_preprint":false},{"year":2025,"finding":"RABEP1 is essential for neutrophil motility and chemotaxis. In RABEP1-deficient zebrafish and human dHL-60 cells, endosomal recycling is impaired, PAK phosphorylation (Rac activation readout) is reduced, and leading-edge F-actin polymerization is decreased, without affecting Rab5-GTP levels or chemokine-induced cell polarization. Re-expression of full-length RABEP1, but not a truncation lacking the Rab4/Rab5 binding domain, rescues motility. Dominant-negative Rab4 or Rab5 similarly inhibit neutrophil migration.","method":"Neutrophil-specific knockout in zebrafish, siRNA knockdown in dHL-60 cells, rescue with domain deletion mutants, dominant-negative Rab4/Rab5 expression, PAK phosphorylation assay, F-actin staining, recycling assays","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO in zebrafish plus human cell knockdown, domain rescue experiment, multiple orthogonal readouts; single lab, published in peer-reviewed journal (2026 paper) with preprint also available","pmids":["41701563","40463167"],"is_preprint":false}],"current_model":"RABEP1 (Rabaptin-5) is a coiled-coil effector protein that binds GTP-Rab5 via its C-terminus and GTP-Rab4 via its N-terminus, forming a homodimer that functions as a molecular linker between these two GTPases to coordinate endocytic membrane fusion and receptor recycling; it forms a critical complex with the Rab5 GEF Rabex-5 (which it allosterically activates), is recruited to early endosomes in a Rab5-GTP-dependent positive feedback loop, interacts with AP-1/GGA clathrin adaptors at the TGN via defined binding motifs, is phosphorylated by PKD at Ser407 to redirect αvβ3 integrin toward short-loop Rab4-dependent recycling and promote cell migration, is cleaved by caspases during apoptosis to block endosome fusion, modulates surface stability of receptors, and drives leading-edge actin polymerization and Rac activation in neutrophil chemotaxis through its endosomal recycling function."},"narrative":{"mechanistic_narrative":"RABEP1 (Rabaptin-5) is a coiled-coil endosomal effector that coordinates Rab GTPase signaling to drive early endosome docking, fusion, and receptor recycling [PMID:8521472]. It functions as a divalent Rab linker: a 73-residue C-terminal region is necessary and sufficient for binding GTP-Rab5 and Rab5-dependent recruitment to early endosomes, while an N-terminal domain binds GTP-Rab4, and native cytosolic protein exists as a coiled-coil-dependent homodimer [PMID:9524117]. Rabaptin-5 forms a tight complex with the Rab5 GEF Rabex-5, increasing its nucleotide exchange activity on Rab5, so that Rab5-GTP recruitment of the Rabaptin-5/Rabex-5 complex generates a positive feedback loop that amplifies Rab5 activation on endosomal membranes [PMID:9323142, PMID:11452015, PMID:20169068]. Through defined motifs—including the FGPLV sequence and C-terminal coiled-coils—it links to clathrin adaptors at the TGN/recycling endosomes, binding the gamma1-adaptin ear of AP-1 and the GAE and GAT domains of GGAs, and the complex negatively regulates Rab4-dependent AP-1/clathrin vesicle formation from endosomes [PMID:11872161, PMID:12505986, PMID:14636058, PMID:15331762]. PKD phosphorylation at Ser407 redirects Rabaptin-5 to preferentially engage Rab4, driving short-loop recycling of αvβ3 integrin to the leading edge and promoting persistent cell migration and invasion [PMID:22975325]; the same recycling activity supports neutrophil motility, where loss of RABEP1 impairs endosomal recycling, Rac/PAK activation, and leading-edge F-actin without affecting bulk Rab5-GTP [PMID:41701563, PMID:40463167]. Rabaptin-5 also stabilizes surface levels of receptors such as FcεRI, β1 integrin, and the KV10.1 channel via its recycling function [PMID:18698003, PMID:22841712]. During apoptosis, caspase cleavage separates its N- and C-terminal Rab5-binding sites, inactivating endosome fusion [PMID:9321397, PMID:16861912]. Activity is further controlled by binding partners HD-PTP/PTPN23, which restrains Rab5 hyperactivation to coordinate ESCRT-dependent MVB sorting [PMID:34657963], and ITSN2L, which promotes RABEP1 degradation [PMID:26633357].","teleology":[{"year":1995,"claim":"Established RABEP1 as a bona fide Rab5 effector required for endosome fusion, defining its core place in the endocytic pathway.","evidence":"Co-IP, cytosol immunodepletion, and in vitro fusion assay with purified early endosomes plus GTP-dependent recruitment","pmids":["8521472"],"confidence":"High","gaps":["Domain basis of Rab5 binding not yet mapped","Did not address other Rab partners or membrane recruitment mechanism"]},{"year":1997,"claim":"Identified the Rabaptin-5/Rabex-5 complex, coupling the effector to a Rab5 GEF and explaining how active Rab5 is generated and stabilized at fusion sites.","evidence":"Mass spec identification, biochemical co-purification, in vitro nucleotide exchange and cell-free fusion assays","pmids":["9323142"],"confidence":"High","gaps":["Directionality of regulation (does Rabaptin-5 activate Rabex-5?) not yet resolved","Stoichiometry of complex unaddressed"]},{"year":1997,"claim":"Showed that caspase cleavage of Rabaptin-5 mechanistically links apoptosis to shutdown of endosome fusion.","evidence":"Cell-free Xenopus apoptosis extract, cleavage immunoblot, caspase inhibitor and Bcl-2/Bcl-xL rescue, fusion assay","pmids":["9321397"],"confidence":"High","gaps":["Exact cleavage sites and responsible caspase not pinpointed","Functional consequence of cleavage on domain separation shown only later"]},{"year":1998,"claim":"Defined Rabaptin-5 as a divalent Rab linker with separate Rab4 (N-terminal) and Rab5 (C-terminal) binding domains, and as a coiled-coil homodimer.","evidence":"Deletion mutagenesis, GST pulldown, yeast two-hybrid, immunofluorescence, gel filtration","pmids":["9524117"],"confidence":"High","gaps":["Functional consequence of simultaneously bridging Rab4 and Rab5 not demonstrated in vivo","Regulation of Rab4 vs Rab5 binding switch unknown at this stage"]},{"year":2001,"claim":"Demonstrated reciprocal allosteric activation—Rabaptin-5 enhances Rabex-5 GEF activity and depends on Rabex-5 for endosomal recruitment—and that the complex is essential for fusion.","evidence":"Reconstitution with recombinant proteins, in vitro GEF, recruitment, and cell-free fusion assays","pmids":["11452015"],"confidence":"High","gaps":["In vivo necessity of Rabaptin-5 for Rabex-5 targeting later challenged","Did not quantify feedback kinetics"]},{"year":2003,"claim":"Mapped the bipartite GGA and AP-1 adaptor binding of Rabaptin-5, placing the complex at the interface of endosomal sorting and TGN clathrin coats.","evidence":"Co-IP, GST pulldown, FGPLV motif mutagenesis, GGA1 GAT crystal structure with reciprocal mutants, relocalization assays","pmids":["12505986","14636058"],"confidence":"High","gaps":["Cargo selectivity conferred by these interactions not defined","In vivo significance at TGN vs endosomes not separated"]},{"year":2004,"claim":"Showed the complex negatively regulates AP-1/clathrin recycling vesicle formation in a Rab4-dependent, Rab5-independent manner, distinguishing its fusion and recycling roles.","evidence":"In vitro vesicle formation assay with biotinylated receptor, immunodepletion, purified protein add-back, BFA controls","pmids":["15331762"],"confidence":"High","gaps":["Molecular switch between fusion-promoting and recycling-regulating modes unknown","Physiological cargo not identified"]},{"year":2007,"claim":"Revised the GEF-targeting model by showing Rabex-5 reaches endosomes and activates Rab5 in vivo via its own EET domain, independent of Rabaptin-5.","evidence":"Rabex-5 deletion mutagenesis, GFP fluorescence microscopy, cellular Rab5-GTP activation assays","pmids":["17699593"],"confidence":"Medium","gaps":["Reconciliation of in vitro requirement vs in vivo dispensability incomplete","Does not exclude amplifying role of Rabaptin-5"]},{"year":2010,"claim":"Formalized the Rabex-5/Rabaptin-5 positive feedback loop as a delayed, threshold-dependent amplifier of Rab5 activation.","evidence":"Kinetic cell-based measurements with varying Rabex-5 levels integrated with mathematical modeling","pmids":["20169068"],"confidence":"Medium","gaps":["Model parameters from single system","Physiological conditions engaging the indirect pathway not defined"]},{"year":2012,"claim":"Identified PKD phosphorylation of Ser407 as a switch directing Rabaptin-5 toward Rab4-dependent short-loop integrin recycling that drives directed cell migration.","evidence":"In vitro kinase assay, phospho-antibodies, S407A/S407D mutagenesis, Rab4/Rab5 co-IP, integrin recycling, migration and invasion assays","pmids":["22975325"],"confidence":"High","gaps":["Structural basis for phospho-dependent Rab4 preference not solved","Upstream signals controlling PKD targeting context-specific"]},{"year":2008,"claim":"Revealed a fusion-independent role: Rabaptin-5 stabilizes cell-surface receptors, tuning immune cell sensitivity.","evidence":"shRNA knockdown in mast cells, flow cytometry of surface FcεRI/β1 integrin, endocytosis and mediator release assays","pmids":["18698003"],"confidence":"Medium","gaps":["Molecular basis of surface stabilization unresolved","Single cell type"]},{"year":2021,"claim":"Placed Rabaptin-5 under negative control by HD-PTP/PTPN23, coordinating Rab5 deactivation and dephosphorylation with ESCRT-dependent MVB cargo sorting.","evidence":"Direct co-IP with domain mapping, ESCRT-III peptide competition, HD-PTP siRNA, Rab5-GTP and phosphorylation analyses","pmids":["34657963"],"confidence":"Medium","gaps":["Whether HD-PTP recruits a phosphatase or competes sterically not fully resolved","Single lab"]},{"year":2025,"claim":"Demonstrated an in vivo physiological requirement for RABEP1 recycling activity in neutrophil chemotaxis via Rac/PAK and leading-edge actin.","evidence":"Neutrophil-specific zebrafish knockout, dHL-60 siRNA, domain-deletion rescue, dominant-negative Rab4/Rab5, PAK phospho and F-actin assays","pmids":["41701563","40463167"],"confidence":"Medium","gaps":["Link between recycled cargo and Rac activation not molecularly defined","Single lab"]},{"year":null,"claim":"How RABEP1 isoforms and post-translational state (phosphorylation, cleavage) are integrated to switch between Rab5-fusion, Rab4-recycling, and TGN/ciliary trafficking functions in a given cell context remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of full-length dimer bound to both Rab4 and Rab5","Isoform-specific (δ, γ) physiological roles uncharacterized","Mendelian disease association absent from this corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,5,17]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[26]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,3]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[8,21,22]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,9,11]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[18,16,21]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[18,26]}],"complexes":["Rabaptin-5/Rabex-5 complex"],"partners":["RABGEF1","RAB5A","RAB4A","AP1G1","GGA1","PTPN23","ITSN2","GAP43"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q15276","full_name":"Rab GTPase-binding effector protein 1","aliases":["Rabaptin-4","Rabaptin-5","Rabaptin-5alpha","Renal carcinoma antigen NY-REN-17"],"length_aa":862,"mass_kda":99.3,"function":"Rab effector protein acting as linker between gamma-adaptin, RAB4A and RAB5A. Involved in endocytic membrane fusion and membrane trafficking of recycling endosomes. Involved in KCNH1 channels trafficking to and from the cell membrane (PubMed:22841712). Forms a complex with RABGEF1 that stimulates RABGEF1-mediated nucleotide exchange on RAB5A (PubMed:9323142). Mediates the traffic of PKD1:PKD2 complex from the endoplasmic reticulum through the Golgi to the cilium (By similarity)","subcellular_location":"Cytoplasm; Early endosome; Recycling endosome; Cytoplasmic vesicle","url":"https://www.uniprot.org/uniprotkb/Q15276/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RABEP1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000029725","cell_line_id":"CID000445","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"RABGEF1","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000445","total_profiled":1310},"omim":[{"mim_id":"616694","title":"ECM29 PROTEASOME ADAPTOR AND SCAFFOLD PROTEIN; ECPAS","url":"https://www.omim.org/entry/616694"},{"mim_id":"611869","title":"RABAPTIN, RAB GTPase-BINDING EFFECTOR PROTEIN 2; RABEP2","url":"https://www.omim.org/entry/611869"},{"mim_id":"608537","title":"VON HIPPEL-LINDAU TUMOR SUPPRESSOR; VHL","url":"https://www.omim.org/entry/608537"},{"mim_id":"607785","title":"JUVENILE MYELOMONOCYTIC LEUKEMIA; JMML","url":"https://www.omim.org/entry/607785"},{"mim_id":"607380","title":"TNF RECEPTOR-ASSOCIATED FACTOR 3-INTERACTING PROTEIN 1; TRAF3IP1","url":"https://www.omim.org/entry/607380"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RABEP1"},"hgnc":{"alias_symbol":["neurocrescin","RAB5EP","RABPT5","rabaptin-5"],"prev_symbol":[]},"alphafold":{"accession":"Q15276","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15276","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q15276-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q15276-F1-predicted_aligned_error_v6.png","plddt_mean":78.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RABEP1","jax_strain_url":"https://www.jax.org/strain/search?query=RABEP1"},"sequence":{"accession":"Q15276","fasta_url":"https://rest.uniprot.org/uniprotkb/Q15276.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q15276/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15276"}},"corpus_meta":[{"pmid":"9323142","id":"PMC_9323142","title":"A novel Rab5 GDP/GTP exchange factor complexed to Rabaptin-5 links nucleotide exchange to effector 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isoform Rabaptin-5delta differ in their ability to interact with the small GTPase Rab4.","date":"2005","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/15634330","citation_count":13,"is_preprint":false},{"pmid":"34657963","id":"PMC_34657963","title":"His domain protein tyrosine phosphatase and Rabaptin-5 couple endo-lysosomal sorting of EGFR with endosomal maturation.","date":"2021","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/34657963","citation_count":12,"is_preprint":false},{"pmid":"26680696","id":"PMC_26680696","title":"The pleckstrin homology domain of phospholipase D1 accelerates EGFR endocytosis by increasing the expression of the Rab5 effector, rabaptin-5.","date":"2015","source":"Experimental & molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/26680696","citation_count":11,"is_preprint":false},{"pmid":"12119113","id":"PMC_12119113","title":"Multiple Rabaptin-5-like 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It is mainly cytosolic but colocalizes with Rab5 on early endosomes; Rab5 recruits it to purified early endosomes in a GTP-dependent manner, and immunodepletion of rabaptin-5 from cytosol strongly inhibits Rab5-dependent early endosome fusion.\",\n      \"method\": \"Co-immunoprecipitation, immunodepletion from cytosol, in vitro endosome fusion assay with purified early endosomes, overexpression with morphological readout (endosome enlargement)\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro reconstitution (endosome fusion assay), immunodepletion rescue, GTP-dependent recruitment to purified organelles; foundational paper replicated extensively\",\n      \"pmids\": [\"8521472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Rabaptin-5 forms a tight physical complex with Rabex-5, a novel 60 kDa Rab5 GDP/GTP exchange factor homologous to yeast Vps9p. This complex is essential for endocytic membrane fusion; Rabex-5 displays GDP/GTP exchange activity on Rab5 upon membrane delivery, and the complex stabilizes Rab5 in the GTP-active state.\",\n      \"method\": \"Nanoelectrospray mass spectrometry identification, biochemical co-purification, in vitro nucleotide exchange assay, cell-free endosome fusion assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro GEF assay, reconstitution of complex, fusion assay; independently replicated\",\n      \"pmids\": [\"9323142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Rabaptin-5 is cleaved by caspase-family proteases during apoptosis, and this selective cleavage is responsible for the block in endosome fusion observed in apoptotic cells. Cleavage was shown in a cell-free Xenopus egg-extract apoptosis system and in cellular apoptosis models; Bcl-2/Bcl-xL or caspase inhibitors prevented both cleavage and fusion inhibition.\",\n      \"method\": \"Cell-free Xenopus egg-extract apoptosis system, immunoblot detection of cleavage, caspase inhibitors, Bcl-2/Bcl-xL rescue, endosome fusion assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reconstituted cell-free system with inhibitor rescue and multiple cellular models; published in high-impact journal with orthogonal approaches\",\n      \"pmids\": [\"9321397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Rabaptin-5 contains two distinct Rab-binding domains: a 73-residue C-terminal region necessary and sufficient for interaction with GTP-bound Rab5 and Rab5-dependent recruitment to early endosomes, and an N-terminal domain that mediates direct interaction with GTP-bound Rab4. Native cytosolic Rabaptin-5 exists as a homodimer dependent on its coiled-coil sequences.\",\n      \"method\": \"Deletion mutagenesis, GST pulldown assays, yeast two-hybrid, immunofluorescence colocalization, gel filtration (native complex analysis)\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple deletion mutants, in vitro binding assays, and localization studies; replicated by subsequent isoform studies\",\n      \"pmids\": [\"9524117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Rabaptin-5 interacts with the neuronal growth-associated protein GAP-43 in a Ca2+-dependent manner, and this interaction modulates endocytosis and synaptic vesicle recycling in neurons.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, endocytosis assays in neuronal cells, overexpression studies\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — yeast two-hybrid plus co-IP plus functional endocytosis assay, single lab\",\n      \"pmids\": [\"9742146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"When physically associated in a complex, Rabaptin-5 increases the nucleotide exchange activity of Rabex-5 on Rab5. Rab5-dependent recruitment of Rabaptin-5 to early endosomes is completely dependent on its physical association with Rabex-5, and complex formation is essential for early endosome homotypic fusion.\",\n      \"method\": \"Reconstitution with recombinant proteins, in vitro GEF assay, endosome recruitment assay, cell-free endosome fusion assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — fully reconstituted with recombinant proteins, multiple orthogonal assays (GEF, recruitment, fusion)\",\n      \"pmids\": [\"11452015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Rabaptin-5 interacts with Rab33b (a Golgi-specific Rab) in its GTP-bound form, suggesting Rabaptin-5 functions not only in the endocytic pathway but also at the Golgi. The interaction was demonstrated by GST-Rab33b pulldown with detection by Western blot and mass spectrometry.\",\n      \"method\": \"GST-Rab33b (GTP-locked) pulldown, Western blot, mass spectrometry\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single pulldown assay, no functional follow-up for Rabaptin-5 specifically at the Golgi\",\n      \"pmids\": [\"11718716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Rabphilin dissociated from Rab3 promotes endocytosis through direct interaction with Rabaptin-5. The Rabphilin V61A mutant (unable to bind Rab3) interacts with Rabaptin-5 and enhances transferrin internalization, whereas Rabphilin L83A fails to bind Rabaptin-5 and does not stimulate endocytosis.\",\n      \"method\": \"Co-immunoprecipitation, transferrin endocytosis assay, point-mutant analysis, overexpression in secretory cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — reciprocal binding data with point mutants, functional endocytosis readout; single lab\",\n      \"pmids\": [\"11309205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Gamma1-adaptin (a subunit of the AP-1 clathrin adaptor complex at the TGN) directly interacts with Rabaptin-5 through its ear domain binding to the C-terminal coiled-coil region of Rabaptin-5. The two proteins colocalize on perinuclear structures (recycling endosomes) and redistribute to cytoplasm upon brefeldin A treatment.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, immunofluorescence colocalization\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — in vitro and in vivo binding confirmed by two methods plus localization; single lab\",\n      \"pmids\": [\"11872161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GGAs (Arf-dependent clathrin adaptors) interact with the Rabaptin-5-Rabex-5 complex via a bipartite mechanism: GGA-GAE domains recognize the FGPLV sequence (residues 439-443) in Rabaptin-5 (also recognized by gamma1- and gamma2-adaptin ears), while GGA-GAT domains bind the C-terminal coiled-coils of Rabaptin-5. GFP-Rabaptin-5 overexpression shifts GGA1 and associated cargo to enlarged early endosomes.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown, site-directed mutagenesis of FGPLV motif, immunofluorescence relocalization assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (pulldown, co-IP, mutagenesis, functional localization shift); replicated in part by GGA1 GAT domain crystal structure studies\",\n      \"pmids\": [\"12505986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The GGA1 GAT domain binds Rabaptin-5 through a hydrophobic surface patch on its C-terminal three-helix bundle. The N284S mutation in this patch reduces Rabaptin-5 binding, and the reciprocal S293N mutation in GGA3 partially confers Rabaptin-5 binding; binding of GAT to Rabaptin-5 is independent of its interaction with ARF.\",\n      \"method\": \"Crystal structure of GGA1 GAT domain, site-directed mutagenesis, in vitro binding assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus mutagenesis and in vitro binding; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"14636058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Rabaptin-5/Rabex-5 complex negatively regulates AP-1/clathrin-coated vesicle formation from endosomes in a Rab4-dependent recycling pathway. Depletion of rabaptin-5/rabex-5 from cytosol stimulated recycling vesicle production, while addition of purified protein strongly inhibited it; Rab4, but not Rab5, was required for this process.\",\n      \"method\": \"In vitro vesicle formation assay using surface-biotinylated receptor, immunodepletion from cytosol, add-back of purified protein, brefeldin A inhibition\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted vesicle formation assay with immunodepletion and add-back; multiple inhibitor controls; single lab\",\n      \"pmids\": [\"15331762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The Rabaptin-5δ isoform interacts with GTP-bound Rab5 but not with Rab4, unlike full-length Rabaptin-5 which binds both. This is due to a disrupted Rab4 binding site caused by the alternative splicing deletion, confirmed by yeast two-hybrid, GST pulldown, and immunofluorescence colocalization.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, immunofluorescence colocalization in BHK-21 cells\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — two orthogonal binding assays plus localization; single lab\",\n      \"pmids\": [\"15634330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Rabaptin-5 exists as a dimer in cells, and its δ and γ isoforms also form dimers, providing the first direct evidence for Rabaptin-5 dimerization in a cellular context. Dimerization was established using biochemical cross-linking and co-immunoprecipitation approaches.\",\n      \"method\": \"Co-immunoprecipitation, cross-linking, biochemical fractionation\",\n      \"journal\": \"Biochemistry. Biokhimiia\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, limited methodological detail in abstract\",\n      \"pmids\": [\"17223781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Rabaptin-5γ and Rabaptin-5δ isoforms are cleaved by caspase-3-related proteases in apoptotic cell extracts, and both contain an N-terminal Rab5 binding site that becomes physically separated from the C-terminal Rab5 binding site after apoptotic cleavage, providing a mechanistic model for inactivation of endosome fusion.\",\n      \"method\": \"In vitro cleavage by caspase-3 in cell extracts, immunoblot detection of cleavage products, mapping of Rab5 binding sites on deletion mutants\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — cell extract cleavage assay plus domain mapping; single lab, builds on prior work\",\n      \"pmids\": [\"16861912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Rabex-5 can target to early endosomes and activate Rab5 in vivo via an early endosomal targeting (EET) domain (residues 81-230) that is independent of its Rabaptin-5-binding domain; Rabaptin-5 is therefore not required for Rabex-5 membrane targeting and Rab5 activation in vivo, despite being required in vitro.\",\n      \"method\": \"Deletion mutagenesis of Rabex-5, fluorescence microscopy of GFP-tagged constructs, Rab5-GTP activation assays in cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic mutagenesis with cellular localization and Rab5 activation readouts; single lab, challenges prior model\",\n      \"pmids\": [\"17699593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In mast cells, Rabaptin-5 knockdown reduces surface expression of FcεRI and β1 integrin (by diminishing receptor surface stability) but does not impair FcεRI internalization or endosome fusion. This receptor surface stabilization function of Rabaptin-5 reduces mast cell sensitivity to antigen-induced mediator release and Ag-induced adhesion/migration.\",\n      \"method\": \"shRNA knockdown, flow cytometry for surface receptor levels, transferrin endocytosis assay, mediator release assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — shRNA knockdown with multiple orthogonal functional readouts; single lab\",\n      \"pmids\": [\"18698003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The Rabex-5/Rabaptin-5 complex forms a positive feedback loop for Rab5 activation on endosomal membranes: Rabaptin-5 binding to Rab5-GTP recruits the Rabex-5/Rabaptin-5 complex to the membrane, where Rabex-5 generates more Rab5-GTP. This indirect pathway has a delayed onset ('delayed response') requiring above-endogenous levels of Rab5 or Rabex-5 to engage.\",\n      \"method\": \"Mathematical modeling, kinetic analysis of Rab5 activation in cells with varying Rabex-5 expression levels, fluorescence assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — kinetic cell-based measurements integrated with mathematical model; single lab\",\n      \"pmids\": [\"20169068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Protein kinase D (PKD) phosphorylates Rabaptin-5 at Ser407, and this phosphorylation is necessary and sufficient for PDGF-dependent short-loop recycling of αvβ3 integrin. Phosphorylated Rabaptin-5 interacts preferentially with Rab4 (not Rab5) near the front of migrating cells to deliver αvβ3 to the leading edge, driving persistent cell migration and invasion, while also inhibiting α5β1 recycling.\",\n      \"method\": \"In vitro kinase assay (PKD phosphorylation of Rabaptin-5), phospho-specific antibodies, site-directed mutagenesis (S407A/S407D), co-immunoprecipitation with Rab4/Rab5, integrin recycling assays, 2D migration and invasion assays\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro kinase assay, phospho-mutagenesis with gain/loss-of-function, multiple functional readouts (recycling, migration, invasion); single lab but multiple orthogonal methods\",\n      \"pmids\": [\"22975325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"KV10.1 potassium channel physically interacts with Rabaptin-5 and colocalizes on large early endosomes induced by Rab5 hyperactivity. Silencing Rabaptin-5 reduces recycling of KV10.1 to the cell surface and decreases KV10.1 current density in cells natively expressing the channel.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence colocalization, siRNA knockdown, whole-cell patch-clamp recording\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — co-IP plus functional knockdown with electrophysiology readout; single lab\",\n      \"pmids\": [\"22841712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In Drosophila, Rabaptin-5 functions as a neoplastic tumor suppressor; loss-of-function mutants cause epithelial disruption and over-proliferation associated with upregulation of JNK and JAK/STAT signaling, without disruption of apico-basal polarity. Its ability to bind Rab5, modulate early endosomal dynamics, and interact with Rabex-5 is conserved in Drosophila.\",\n      \"method\": \"Genetic mosaic analysis in Drosophila (loss-of-function mutations), epistasis with JNK/JAK-STAT pathway reporters, Rab5 binding assays\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in Drosophila with signaling pathway readouts; conserved protein, single study\",\n      \"pmids\": [\"24104056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Rabep1 couples the polycystin complex (PC1/PC2) to a GGA1/Arl3-based ciliary trafficking module at the TGN, enabling ciliary targeting of these large transmembrane proteins. This was identified by yeast two-hybrid screening and validated with a candidate approach.\",\n      \"method\": \"Yeast two-hybrid screening, co-immunoprecipitation, candidate interaction validation, knockdown with ciliary localization readout\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — yeast two-hybrid plus co-IP and functional ciliary targeting assay; single lab\",\n      \"pmids\": [\"25405894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The Rabaptin-5γ isoform, despite its ability to interact with Rab5, is absent from early endosomes and is instead localized to the trans-Golgi network and a Rab4-positive compartment, indicating it functions in membrane transport steps other than Rab5-driven early endosome fusion.\",\n      \"method\": \"Immunofluorescence microscopy, subcellular fractionation, Rab5/Rab4 co-localization analysis in transfected cells\",\n      \"journal\": \"Biochemistry. Biokhimiia\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — localization data without mechanistic functional follow-up; single lab\",\n      \"pmids\": [\"25385014\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HDAC6 overexpression in gastric cancer inhibits rabaptin-5-mediated early endosome fusion, thereby prolonging EGFR activation and sustaining growth stimulation. HDAC6 knockdown caused inhibition of gastric cancer cell growth associated with decreased EGFR signaling.\",\n      \"method\": \"HDAC6 shRNA knockdown, EGFR signaling assays, endosome fusion assays, cell growth assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — abstract does not detail direct mechanistic link between HDAC6 and Rabaptin-5; limited methodological detail about the Rabaptin-5-specific mechanism\",\n      \"pmids\": [\"25111897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ITSN2L (Intersectin-2Long) interacts with Rabaptin-5 (RABEP1) via its CC domain binding to the CC3 region of RABEP1. ITSN2L overexpression promotes RABEP1 degradation and represses RABEP1-enhanced endosome aggregation, functioning as a negative regulator of RABEP1 in endocytosis.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, colocalization microscopy, overexpression with endosome morphology readout\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — yeast two-hybrid plus GST pulldown plus co-IP, functional endosome assay; single lab\",\n      \"pmids\": [\"26633357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HD-PTP (PTPN23) binds directly to Rabaptin-5 between its Rabex-5- and Rab5-binding domains, at the same site that interacts with ESCRT-0/ESCRT-III. HD-PTP depletion leads to Rabaptin-5-dependent hyperactivation of Rab5 and accumulation of hyperphosphorylated Rabaptin-5, blocking cargo exit from Rab5-rich endosomes. This indicates HD-PTP coordinates MVB sorting with endosomal maturation by modulating Rabex-5-Rabaptin-5 activity.\",\n      \"method\": \"Co-immunoprecipitation (direct binding), siRNA depletion of HD-PTP, phosphorylation analysis of Rabaptin-5, Rab5-GTP activation assay, ESCRT-III peptide competition binding assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding mapped to defined domains, competition assay, functional knockdown with Rab5 activation readout; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"34657963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RABEP1 is essential for neutrophil motility and chemotaxis. In RABEP1-deficient zebrafish and human dHL-60 cells, endosomal recycling is impaired, PAK phosphorylation (Rac activation readout) is reduced, and leading-edge F-actin polymerization is decreased, without affecting Rab5-GTP levels or chemokine-induced cell polarization. Re-expression of full-length RABEP1, but not a truncation lacking the Rab4/Rab5 binding domain, rescues motility. Dominant-negative Rab4 or Rab5 similarly inhibit neutrophil migration.\",\n      \"method\": \"Neutrophil-specific knockout in zebrafish, siRNA knockdown in dHL-60 cells, rescue with domain deletion mutants, dominant-negative Rab4/Rab5 expression, PAK phosphorylation assay, F-actin staining, recycling assays\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO in zebrafish plus human cell knockdown, domain rescue experiment, multiple orthogonal readouts; single lab, published in peer-reviewed journal (2026 paper) with preprint also available\",\n      \"pmids\": [\"41701563\", \"40463167\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RABEP1 (Rabaptin-5) is a coiled-coil effector protein that binds GTP-Rab5 via its C-terminus and GTP-Rab4 via its N-terminus, forming a homodimer that functions as a molecular linker between these two GTPases to coordinate endocytic membrane fusion and receptor recycling; it forms a critical complex with the Rab5 GEF Rabex-5 (which it allosterically activates), is recruited to early endosomes in a Rab5-GTP-dependent positive feedback loop, interacts with AP-1/GGA clathrin adaptors at the TGN via defined binding motifs, is phosphorylated by PKD at Ser407 to redirect αvβ3 integrin toward short-loop Rab4-dependent recycling and promote cell migration, is cleaved by caspases during apoptosis to block endosome fusion, modulates surface stability of receptors, and drives leading-edge actin polymerization and Rac activation in neutrophil chemotaxis through its endosomal recycling function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RABEP1 (Rabaptin-5) is a coiled-coil endosomal effector that coordinates Rab GTPase signaling to drive early endosome docking, fusion, and receptor recycling [#0]. It functions as a divalent Rab linker: a 73-residue C-terminal region is necessary and sufficient for binding GTP-Rab5 and Rab5-dependent recruitment to early endosomes, while an N-terminal domain binds GTP-Rab4, and native cytosolic protein exists as a coiled-coil-dependent homodimer [#3]. Rabaptin-5 forms a tight complex with the Rab5 GEF Rabex-5, increasing its nucleotide exchange activity on Rab5, so that Rab5-GTP recruitment of the Rabaptin-5/Rabex-5 complex generates a positive feedback loop that amplifies Rab5 activation on endosomal membranes [#1, #5, #17]. Through defined motifs—including the FGPLV sequence and C-terminal coiled-coils—it links to clathrin adaptors at the TGN/recycling endosomes, binding the gamma1-adaptin ear of AP-1 and the GAE and GAT domains of GGAs, and the complex negatively regulates Rab4-dependent AP-1/clathrin vesicle formation from endosomes [#8, #9, #10, #11]. PKD phosphorylation at Ser407 redirects Rabaptin-5 to preferentially engage Rab4, driving short-loop recycling of αvβ3 integrin to the leading edge and promoting persistent cell migration and invasion [#18]; the same recycling activity supports neutrophil motility, where loss of RABEP1 impairs endosomal recycling, Rac/PAK activation, and leading-edge F-actin without affecting bulk Rab5-GTP [#26]. Rabaptin-5 also stabilizes surface levels of receptors such as FcεRI, β1 integrin, and the KV10.1 channel via its recycling function [#16, #19]. During apoptosis, caspase cleavage separates its N- and C-terminal Rab5-binding sites, inactivating endosome fusion [#2, #14]. Activity is further controlled by binding partners HD-PTP/PTPN23, which restrains Rab5 hyperactivation to coordinate ESCRT-dependent MVB sorting [#25], and ITSN2L, which promotes RABEP1 degradation [#24].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established RABEP1 as a bona fide Rab5 effector required for endosome fusion, defining its core place in the endocytic pathway.\",\n      \"evidence\": \"Co-IP, cytosol immunodepletion, and in vitro fusion assay with purified early endosomes plus GTP-dependent recruitment\",\n      \"pmids\": [\"8521472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Domain basis of Rab5 binding not yet mapped\", \"Did not address other Rab partners or membrane recruitment mechanism\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Identified the Rabaptin-5/Rabex-5 complex, coupling the effector to a Rab5 GEF and explaining how active Rab5 is generated and stabilized at fusion sites.\",\n      \"evidence\": \"Mass spec identification, biochemical co-purification, in vitro nucleotide exchange and cell-free fusion assays\",\n      \"pmids\": [\"9323142\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Directionality of regulation (does Rabaptin-5 activate Rabex-5?) not yet resolved\", \"Stoichiometry of complex unaddressed\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showed that caspase cleavage of Rabaptin-5 mechanistically links apoptosis to shutdown of endosome fusion.\",\n      \"evidence\": \"Cell-free Xenopus apoptosis extract, cleavage immunoblot, caspase inhibitor and Bcl-2/Bcl-xL rescue, fusion assay\",\n      \"pmids\": [\"9321397\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact cleavage sites and responsible caspase not pinpointed\", \"Functional consequence of cleavage on domain separation shown only later\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined Rabaptin-5 as a divalent Rab linker with separate Rab4 (N-terminal) and Rab5 (C-terminal) binding domains, and as a coiled-coil homodimer.\",\n      \"evidence\": \"Deletion mutagenesis, GST pulldown, yeast two-hybrid, immunofluorescence, gel filtration\",\n      \"pmids\": [\"9524117\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of simultaneously bridging Rab4 and Rab5 not demonstrated in vivo\", \"Regulation of Rab4 vs Rab5 binding switch unknown at this stage\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrated reciprocal allosteric activation—Rabaptin-5 enhances Rabex-5 GEF activity and depends on Rabex-5 for endosomal recruitment—and that the complex is essential for fusion.\",\n      \"evidence\": \"Reconstitution with recombinant proteins, in vitro GEF, recruitment, and cell-free fusion assays\",\n      \"pmids\": [\"11452015\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo necessity of Rabaptin-5 for Rabex-5 targeting later challenged\", \"Did not quantify feedback kinetics\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mapped the bipartite GGA and AP-1 adaptor binding of Rabaptin-5, placing the complex at the interface of endosomal sorting and TGN clathrin coats.\",\n      \"evidence\": \"Co-IP, GST pulldown, FGPLV motif mutagenesis, GGA1 GAT crystal structure with reciprocal mutants, relocalization assays\",\n      \"pmids\": [\"12505986\", \"14636058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cargo selectivity conferred by these interactions not defined\", \"In vivo significance at TGN vs endosomes not separated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed the complex negatively regulates AP-1/clathrin recycling vesicle formation in a Rab4-dependent, Rab5-independent manner, distinguishing its fusion and recycling roles.\",\n      \"evidence\": \"In vitro vesicle formation assay with biotinylated receptor, immunodepletion, purified protein add-back, BFA controls\",\n      \"pmids\": [\"15331762\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular switch between fusion-promoting and recycling-regulating modes unknown\", \"Physiological cargo not identified\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Revised the GEF-targeting model by showing Rabex-5 reaches endosomes and activates Rab5 in vivo via its own EET domain, independent of Rabaptin-5.\",\n      \"evidence\": \"Rabex-5 deletion mutagenesis, GFP fluorescence microscopy, cellular Rab5-GTP activation assays\",\n      \"pmids\": [\"17699593\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation of in vitro requirement vs in vivo dispensability incomplete\", \"Does not exclude amplifying role of Rabaptin-5\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Formalized the Rabex-5/Rabaptin-5 positive feedback loop as a delayed, threshold-dependent amplifier of Rab5 activation.\",\n      \"evidence\": \"Kinetic cell-based measurements with varying Rabex-5 levels integrated with mathematical modeling\",\n      \"pmids\": [\"20169068\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Model parameters from single system\", \"Physiological conditions engaging the indirect pathway not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified PKD phosphorylation of Ser407 as a switch directing Rabaptin-5 toward Rab4-dependent short-loop integrin recycling that drives directed cell migration.\",\n      \"evidence\": \"In vitro kinase assay, phospho-antibodies, S407A/S407D mutagenesis, Rab4/Rab5 co-IP, integrin recycling, migration and invasion assays\",\n      \"pmids\": [\"22975325\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for phospho-dependent Rab4 preference not solved\", \"Upstream signals controlling PKD targeting context-specific\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed a fusion-independent role: Rabaptin-5 stabilizes cell-surface receptors, tuning immune cell sensitivity.\",\n      \"evidence\": \"shRNA knockdown in mast cells, flow cytometry of surface FcεRI/β1 integrin, endocytosis and mediator release assays\",\n      \"pmids\": [\"18698003\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of surface stabilization unresolved\", \"Single cell type\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed Rabaptin-5 under negative control by HD-PTP/PTPN23, coordinating Rab5 deactivation and dephosphorylation with ESCRT-dependent MVB cargo sorting.\",\n      \"evidence\": \"Direct co-IP with domain mapping, ESCRT-III peptide competition, HD-PTP siRNA, Rab5-GTP and phosphorylation analyses\",\n      \"pmids\": [\"34657963\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether HD-PTP recruits a phosphatase or competes sterically not fully resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated an in vivo physiological requirement for RABEP1 recycling activity in neutrophil chemotaxis via Rac/PAK and leading-edge actin.\",\n      \"evidence\": \"Neutrophil-specific zebrafish knockout, dHL-60 siRNA, domain-deletion rescue, dominant-negative Rab4/Rab5, PAK phospho and F-actin assays\",\n      \"pmids\": [\"41701563\", \"40463167\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link between recycled cargo and Rac activation not molecularly defined\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RABEP1 isoforms and post-translational state (phosphorylation, cleavage) are integrated to switch between Rab5-fusion, Rab4-recycling, and TGN/ciliary trafficking functions in a given cell context remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of full-length dimer bound to both Rab4 and Rab5\", \"Isoform-specific (δ, γ) physiological roles uncharacterized\", \"Mendelian disease association absent from this corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 5, 17]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [8, 21, 22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 9, 11]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [18, 16, 21]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [18, 26]}\n    ],\n    \"complexes\": [\"Rabaptin-5/Rabex-5 complex\"],\n    \"partners\": [\"RABGEF1\", \"RAB5A\", \"RAB4A\", \"AP1G1\", \"GGA1\", \"PTPN23\", \"ITSN2\", \"GAP43\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}