{"gene":"CCZ1","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2010,"finding":"The dimeric Mon1-Ccz1 complex is the guanine nucleotide exchange factor (GEF) for the late endosomal Rab7 homolog Ypt7 in yeast. Neither protein alone has GEF activity; only the complex counteracts GAP function in vivo, rescues in vitro fusion of vacuoles carrying Ypt7-GDP, and promotes nucleotide exchange on Ypt7 independently of Vps39/HOPS.","method":"In vitro nucleotide exchange assay, in vivo GAP counteraction assay, in vitro vacuole fusion rescue assay","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 — reconstituted GEF activity in vitro with multiple orthogonal assays; foundational paper with 317 citations","pmids":["20797862"],"is_preprint":false},{"year":2002,"finding":"Mon1 and Ccz1 physically interact as a stable protein complex (Ccz1-Mon1 complex) that peripherally associates with a perivacuolar compartment and vacuole membrane. The complex is required for the late fusion step in multiple vacuole delivery pathways (Cvt, autophagy, pexophagy, CPY, ALP, MVB pathways), functioning after vesicle formation but before or at fusion with the vacuole.","method":"Co-immunoprecipitation, subcellular fractionation, fluorescence microscopy, genetic deletion analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus fractionation plus multiple pathway genetic analysis; 104 citations","pmids":["12364329"],"is_preprint":false},{"year":2003,"finding":"The Ccz1-Mon1 complex binds the vacuole membrane and is required for the tethering/docking stage of homotypic vacuole fusion. In its absence, vacuole SNARE pairing and HOPS complex interaction are impaired. The complex colocalizes with other fusion components in the cis-SNARE complex, and its vacuole association is regulated by the class C Vps/HOPS complex.","method":"In vitro homotypic vacuole fusion assay, co-immunoprecipitation, fluorescence microscopy, biochemical fractionation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro fusion assay combined with Co-IP and localization; 94 citations","pmids":["14662743"],"is_preprint":false},{"year":2001,"finding":"Ccz1 physically interacts with the Rab GTPase Ypt7. Extragenic suppressors of CCZ1 deletion are gain-of-function alleles of YPT7 with mutations in guanine-binding domains, and co-immunoprecipitation confirms direct physical interaction between Ccz1 and Ypt7.","method":"Extragenic suppressor screen, co-immunoprecipitation","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis plus direct Co-IP; 46 citations","pmids":["11590240"],"is_preprint":false},{"year":2014,"finding":"The Mon1-Ccz1 GEF complex is recruited to vacuoles via phosphatidylinositol 3-phosphate (PI3P). After activating Ypt7, Mon1 is phosphorylated by the type 1 casein kinase Yck3, which triggers Mon1 release from vacuoles for recycling. Mutation of Mon1 phosphorylation sites retains Mon1 on vacuoles.","method":"In vitro competition assay with PI3P, recombinant Yck3 phosphorylation assay, phosphosite mutagenesis, vacuole binding assays","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro reconstitution of phosphorylation plus mutagenesis plus lipid binding competition; multiple orthogonal methods","pmids":["24623720"],"is_preprint":false},{"year":2015,"finding":"In mammalian cells, Mon1-Ccz1 activates RAB7 specifically on late endosomes but dissociates from lysosomes. RAB7 activation on late endosomes by Mon1-Ccz1 is required for late endosome-lysosome fusion, whereas RAB7 activity on lysosomes is Mon1-Ccz1-independent and contributes to perinuclear lysosome clustering.","method":"FRET-based RAB7 activity sensor, confocal imaging, knockdown of Mon1-Ccz1","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — live-cell FRET sensor with spatial resolution and functional knockdown","pmids":["26627821"],"is_preprint":false},{"year":2016,"finding":"In Drosophila, the Ccz1-Mon1-Rab7 module is required for autophagosome-lysosome fusion. Loss of Ccz1-Mon1-Rab7 causes autophagosome accumulation due to failed lysosomal fusion, whereas Rab5 is dispensable for Ccz1-Mon1-dependent Rab7 recruitment to PI3P-positive autophagosomes (generated by Atg14-containing Vps34 complex) during starvation.","method":"Genetic loss-of-function in Drosophila fat cells, fluorescence microscopy, epistasis analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with defined cellular phenotype and pathway epistasis; 166 citations","pmids":["27559127"],"is_preprint":false},{"year":2017,"finding":"C18orf8/RMC1 is a novel subunit of the CCZ1-MON1 RAB7 GEF complex in mammals that positively regulates RAB7 recruitment to late endosomes/autophagosomes. It was identified through interaction proteomics of proteins accumulating in GABARAP/L1/L2-deficient cells.","method":"Interaction proteomics (AP-MS), genetic KO of ATG8 subfamily members, quantitative proteomics of autophagosomes","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2–3 — interaction proteomics plus functional validation in KO cells; 104 citations","pmids":["29038162"],"is_preprint":false},{"year":2018,"finding":"Mon1-Ccz1 is specifically recruited to the pre-autophagosomal structure (PAS) during starvation through direct binding of at least one LIR motif in the Ccz1 C-terminus to Atg8 (yeast LC3 homolog). This LIR motif is essential for autophagy but dispensable for endosomal transport. Wild-type but not LIR-mutated Mon1-Ccz1 promotes Atg8-dependent activation of Ypt7.","method":"LIR motif mutagenesis, in vitro binding assays, autophagy and endosomal transport functional assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis with in vitro binding validation and separate functional readouts for two pathways; 77 citations","pmids":["29446751"],"is_preprint":false},{"year":2021,"finding":"C5orf51 interacts with GDP-locked RAB7A and with MON1 and CCZ1 subunits of the RAB7 GEF complex. In the absence of C5orf51, RAB7A localization on depolarized mitochondria is compromised and RAB7A is degraded by the proteasome, impairing mitophagy. C5orf51 depletion also inhibits ATG9A recruitment to depolarized mitochondria.","method":"Proximity-dependent biotinylation (miniTurbo), genetic KO, mitophagy functional assays, proteasome inhibitor rescue","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2–3 — BioID proximity screen plus functional KO validation; 32 citations","pmids":["34432599"],"is_preprint":false},{"year":2022,"finding":"The lysosomal V-ATPase a3 subunit interacts with the Mon1A-Ccz1 complex through the amino-terminal half domain of a3 and the longin motifs of Mon1A and Ccz1. This interaction localizes Mon1A-Ccz1 to secretory lysosomes in osteoclasts to mediate RAB7 recruitment, which is essential for bone resorption.","method":"Co-immunoprecipitation in HEK293T cells, domain mapping, osteoclast localization of endogenous Ccz1 in a3-KO cells","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP with domain mapping plus endogenous localization in KO cells","pmids":["35589873"],"is_preprint":false},{"year":2022,"finding":"CCZ1 is an essential host factor for Marburg and Ebola filovirus infections, controlling early-to-late endosomal trafficking of these viruses. CCZ1 also contributes to endosomal trafficking of endocytosis-dependent SARS-CoV-2. Inhibition of CCZ1 nearly completely abolishes Marburg and Ebola infections in 3D primary human hepatocyte cultures and blood-vessel organoids.","method":"Haploid cell genetic screen, CCZ1 KO validation in 3D human organoids and cell lines, viral infection assays","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide screen plus validation in primary human tissue models with mechanistic specificity","pmids":["37880247"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structure of the metazoan Mon1-Ccz1-Bulli (MCBulli) complex was solved at 3.2 Å. Bulli associates as a leg-like extension at the periphery of the Mon1-Ccz1 heterodimer without impacting GEF activity or interactions with recruiter/substrate GTPases. Mon1 and Ccz1 constitute the active site of the complex. MCBulli shows structural homology to the Fuzzy-Inturned-Wdpcp (ciliogenesis) complex, but with divergent architecture suggesting Bulli serves as a recruitment platform for endolysosomal trafficking regulators.","method":"Cryo-electron microscopy at 3.2 Å resolution, structural comparison","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — near-atomic resolution cryo-EM structure with functional interpretation","pmids":["37155863"],"is_preprint":false},{"year":2023,"finding":"An amphipathic helix in Ccz1 is required for Mon1-Ccz1 function in autophagy but not endosomal maturation. Mon1 basic patches bind positively charged lipids, and the Ccz1 amphipathic helix interacts with lipid packing defects. A synergistic combination of protein-lipid interactions and recruiter protein associations governs differential targeting of Mon1-Ccz1 to endosomes versus autophagosomes. Membrane binding enhances MC1 GEF activity primarily by increasing enzyme-substrate concentration.","method":"Mutagenesis of amphipathic helix and Mon1 basic patches, lipid binding assays, in vitro GEF activity assays, autophagy and endosomal transport functional assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with in vitro lipid binding and GEF activity assays with separate pathway readouts","pmids":["36649906"],"is_preprint":false},{"year":2022,"finding":"The CCZ1-MON1A complex activity as RAB7 GEF is impaired in Alzheimer's disease models, leading to reduced active RAB7 on autophagosomes and defective autophagosome maturation. Overexpression of CCZ1-MON1A increases active RAB7, enhances autophagosome maturation, and promotes degradation of APP-CTFs, Aβ and P-tau in an autophagy-dependent manner.","method":"GST-R7BD affinity-isolation assay for GTP-RAB7 on autophagosome fractions, AAV-mediated overexpression and knockdown in mouse brain, immunoblotting","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical assay of RAB7 activity on purified autophagosomes plus in vivo functional validation","pmids":["35198070"],"is_preprint":false},{"year":2025,"finding":"Structural and functional comparison revealed that dimeric Mon1-Ccz1 from fungi and metazoan Mon1-Ccz1-RMC1/Bulli bind membranes through electrostatic interactions via distinct interfaces. RMC1/Bulli serves as an essential mediator of GEF complex membrane recruitment in metazoans. Both Mon1-Ccz1 and Fuzzy-Inturned complexes rely on a conserved sequence motif in their substrate GTPases for the catalytic mechanism, while secondary interactions provide target discrimination.","method":"Cryo-EM structure determination, protein-lipid interaction studies, in vitro reconstitution, functional characterization in Drosophila","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure combined with in vitro reconstitution and in vivo Drosophila functional validation","pmids":["40864718"],"is_preprint":false},{"year":2010,"finding":"In C. elegans, CCZ-1 mediates digestion of apoptotic corpses by acting in lysosome biogenesis and phagosome maturation, recruiting the GTPase RAB-7 to phagosomes.","method":"Genetic loss-of-function in C. elegans, fluorescence microscopy of phagosome maturation markers","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — clean genetic KO with defined cellular phenotype and RAB-7 localization readout in C. elegans ortholog","pmids":["20519582"],"is_preprint":false}],"current_model":"CCZ1 forms an obligate heterodimeric (or trimeric with RMC1/Bulli in metazoans) guanine nucleotide exchange factor complex with MON1 that activates the late-endosomal Rab GTPase RAB7/Ypt7 on late endosomes and autophagosomes; the complex is recruited to membranes via PI3P binding, basic-patch electrostatic interactions, a Ccz1 amphipathic helix sensing lipid packing defects, and direct interaction with Atg8/LC3 through a Ccz1 LIR motif for autophagosomal targeting; after RAB7 activation, Mon1 is phosphorylated by casein kinase Yck3 and released for recycling; the metazoan third subunit RMC1/Bulli mediates membrane recruitment and serves as a platform for additional regulators; and the complex is essential for late endosome maturation, autophagosome-lysosome fusion, and multiple vacuole delivery pathways."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing that Ccz1 physically and genetically interacts with the Rab GTPase Ypt7 placed Ccz1 upstream of Ypt7 in vacuolar trafficking before its enzymatic function was known.","evidence":"Extragenic suppressor screen yielding gain-of-function YPT7 alleles plus co-immunoprecipitation in yeast","pmids":["11590240"],"confidence":"Medium","gaps":["Enzymatic mechanism unknown—whether Ccz1 acts as a GEF, effector, or scaffold was unresolved","No in vitro nucleotide exchange data"]},{"year":2002,"claim":"Demonstrating that Mon1 and Ccz1 form a stable complex required for the fusion step in multiple vacuole delivery pathways (Cvt, autophagy, pexophagy, CPY, ALP, MVB) defined the obligate heterodimer and its broad pathway requirement.","evidence":"Reciprocal co-immunoprecipitation, subcellular fractionation, and deletion analysis across six vacuolar pathways in yeast","pmids":["12364329"],"confidence":"High","gaps":["Molecular activity of the complex (GEF, tether, or other) was uncharacterized","How the complex is recruited to membranes was unknown"]},{"year":2003,"claim":"Showing that the Ccz1–Mon1 complex is required at the tethering/docking stage of homotypic vacuole fusion and that its membrane association depends on the HOPS complex resolved where in the fusion cascade it acts.","evidence":"In vitro homotypic vacuole fusion assay, SNARE pairing analysis, and HOPS-dependent membrane association in yeast","pmids":["14662743"],"confidence":"High","gaps":["Direct GEF activity had not been biochemically demonstrated","Relationship between HOPS regulation and Ypt7 activation was unclear"]},{"year":2010,"claim":"Reconstituting Mon1–Ccz1 as the Ypt7 GEF in vitro answered the central mechanistic question: the complex directly catalyzes GDP-to-GTP exchange on Ypt7, independently of the HOPS subunit Vps39.","evidence":"In vitro nucleotide exchange assay, in vivo GAP counteraction, and vacuole fusion rescue with Ypt7-GDP in yeast","pmids":["20797862"],"confidence":"High","gaps":["Structural basis for catalysis unknown","Whether GEF activity is conserved in metazoans was untested"]},{"year":2010,"claim":"Parallel work in C. elegans demonstrated conserved function: CCZ-1 recruits RAB-7 to phagosomes for apoptotic corpse clearance, extending the GEF paradigm to phagosome maturation in metazoans.","evidence":"Genetic loss-of-function and fluorescence imaging of RAB-7 recruitment to phagosomes in C. elegans","pmids":["20519582"],"confidence":"Medium","gaps":["Direct GEF activity was not biochemically tested in the metazoan system","Whether the phagosomal and endosomal functions are mechanistically identical was unclear"]},{"year":2014,"claim":"Identifying PI3P as the membrane recruitment signal and Yck3-mediated phosphorylation of Mon1 as the release mechanism established the lipid-dependent recruitment cycle governing GEF complex dynamics on vacuoles.","evidence":"In vitro PI3P competition assay, recombinant Yck3 phosphorylation, phosphosite mutagenesis in yeast","pmids":["24623720"],"confidence":"High","gaps":["Whether metazoan Mon1–Ccz1 uses the same PI3P-dependent recruitment was untested","No structural view of lipid interaction"]},{"year":2015,"claim":"Demonstrating that mammalian Mon1–Ccz1 activates RAB7 specifically on late endosomes but not lysosomes showed spatial restriction of GEF activity, distinguishing endosome maturation from lysosome maintenance.","evidence":"FRET-based RAB7 activity sensor and knockdown in mammalian cells","pmids":["26461827"],"confidence":"Medium","gaps":["Mechanism of spatial restriction (why Mon1–Ccz1 dissociates from lysosomes) was unknown","Identity of lysosomal RAB7 GEF or stabilizer not established"]},{"year":2016,"claim":"Genetic analysis in Drosophila proved that Ccz1–Mon1–Rab7 is essential for autophagosome–lysosome fusion and showed that PI3P generated by the Atg14-containing Vps34 complex—not Rab5—recruits the GEF, resolving the upstream signal for autophagy-specific targeting.","evidence":"Genetic knockout in Drosophila fat cells with epistasis between Atg14, Rab5, and Ccz1–Mon1–Rab7","pmids":["27559127"],"confidence":"High","gaps":["Direct binding of Ccz1 to autophagosomes was not molecularly defined","Whether additional autophagy-specific recruiters exist was unknown"]},{"year":2017,"claim":"Discovery of C18orf8/RMC1 as a third subunit of the metazoan complex revealed that the mammalian GEF is a heterotrimer, raising questions about how the additional subunit modulates function.","evidence":"Interaction proteomics (AP-MS) in GABARAP-family knockout cells","pmids":["29038162"],"confidence":"Medium","gaps":["Structural role of RMC1 was undefined","Whether RMC1 affects GEF catalytic activity was unknown"]},{"year":2018,"claim":"Identification of a LIR motif in the Ccz1 C-terminus that directly binds Atg8 explained how Mon1–Ccz1 is selectively recruited to autophagosomes for autophagy-specific Ypt7 activation, while being dispensable for endosomal transport.","evidence":"LIR motif mutagenesis, in vitro Atg8 binding, and separate autophagy versus endosomal functional assays in yeast","pmids":["29446751"],"confidence":"High","gaps":["Whether the LIR motif is conserved and functional in metazoan CCZ1 was untested","Structural basis of LIR–Atg8 interaction was lacking"]},{"year":2022,"claim":"Interaction mapping between the V-ATPase a3 subunit and the longin motifs of Mon1A and Ccz1 revealed a tissue-specific recruitment mechanism localizing the GEF to secretory lysosomes in osteoclasts for bone resorption.","evidence":"Co-immunoprecipitation with domain mapping in HEK293T cells and endogenous Ccz1 localization in a3-KO osteoclasts","pmids":["35589873"],"confidence":"Medium","gaps":["Whether a3–Mon1A–Ccz1 interaction is direct or scaffolded was not resolved with purified components","Functional rescue of bone resorption by reconstituted complex was not shown"]},{"year":2022,"claim":"Demonstrating that CCZ1 is an essential host factor for filovirus and endocytosis-dependent SARS-CoV-2 infection connected endosomal RAB7 activation to viral entry, establishing CCZ1 as a potential antiviral target.","evidence":"Haploid genetic screen validated by CCZ1 KO in 3D human hepatocyte cultures and blood-vessel organoids","pmids":["37880247"],"confidence":"Medium","gaps":["Precise step in viral trafficking controlled by CCZ1 (early-to-late endosome transition vs. membrane fusion) was not resolved","Whether CCZ1 inhibition is therapeutically viable without disrupting normal endolysosomal trafficking was not addressed"]},{"year":2022,"claim":"Linking impaired CCZ1–MON1A GEF activity to defective autophagosome maturation in Alzheimer's disease models, with rescue by overexpression, established a disease-relevant consequence of reduced RAB7 activation on autophagosomes.","evidence":"GST-R7BD affinity isolation of GTP-RAB7 on purified autophagosomes, AAV-mediated expression in mouse brain","pmids":["35198070"],"confidence":"Medium","gaps":["Causal mechanism of CCZ1–MON1A impairment in AD was not identified","Whether therapeutic augmentation of GEF activity is feasible in human neurons was untested"]},{"year":2023,"claim":"The 3.2 Å cryo-EM structure of the metazoan Mon1–Ccz1–Bulli trimer showed that Bulli forms a peripheral leg-like extension without contacting the GEF active site, establishing it as a recruitment platform rather than a catalytic modulator.","evidence":"Cryo-EM at 3.2 Å resolution with structural comparison to the Fuzzy–Inturned–Wdpcp ciliogenesis complex","pmids":["37155863"],"confidence":"High","gaps":["Structure of the complex bound to Rab7 substrate was not captured","How Bulli recruits specific regulators was structurally uncharacterized"]},{"year":2023,"claim":"Dissecting the Ccz1 amphipathic helix and Mon1 basic patches revealed a synergistic lipid-sensing mechanism that differentially targets the complex to endosomes versus autophagosomes, with membrane binding enhancing GEF activity by concentrating enzyme and substrate.","evidence":"Mutagenesis of amphipathic helix and basic patches combined with in vitro lipid binding and GEF assays, plus separate autophagy and endosomal functional readouts in yeast","pmids":["36649906"],"confidence":"High","gaps":["Structural visualization of the amphipathic helix inserted into membranes was not achieved","Whether the same lipid-sensing logic operates in metazoan cells was not directly tested"]},{"year":2025,"claim":"Comparative cryo-EM and functional analysis confirmed that RMC1/Bulli mediates membrane recruitment through electrostatic interfaces distinct from the fungal dimer, and identified a conserved GTPase sequence motif recognized by both Mon1–Ccz1 and the structurally related Fuzzy–Inturned complex, unifying the catalytic mechanism across Rab and Rsg1 substrates.","evidence":"Cryo-EM structures, protein-lipid interaction assays, in vitro reconstitution, and Drosophila functional validation","pmids":["40864718"],"confidence":"High","gaps":["Transition-state structure of the GEF–Rab7 catalytic intermediate is still missing","How target discrimination is achieved at the single-residue level beyond the conserved motif remains unresolved"]},{"year":null,"claim":"Key open questions include: the transition-state structure of Mon1–Ccz1 bound to nucleotide-free Rab7; the identity and regulation of upstream signals that inactivate or degrade the complex in metazoans; and whether pharmacological modulation of CCZ1-dependent GEF activity can be achieved for antiviral or neurodegenerative disease applications.","evidence":"","pmids":[],"confidence":"Low","gaps":["No transition-state GEF–Rab7 complex structure","Metazoan recycling mechanism (analogous to Yck3 phosphorylation) not identified","No pharmacological tools to modulate Mon1–Ccz1 activity"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,5,6,14]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[4,13]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1,2,5,11]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[5,10,16]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,6,8]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,2,5,11]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[6,8,13,14]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[5,10,16]}],"complexes":["Mon1-Ccz1 (heterodimer)","Mon1-Ccz1-RMC1/Bulli (metazoan heterotrimer)"],"partners":["MON1A","MON1B","YPT7","RAB7A","RMC1","ATG8","ATP6V0A3"],"other_free_text":[]},"mechanistic_narrative":"CCZ1 is an essential subunit of the Mon1–Ccz1 guanine nucleotide exchange factor (GEF) complex that activates the late-endosomal Rab GTPase RAB7/Ypt7 to drive endosome maturation, autophagosome–lysosome fusion, and phagosome maturation across eukaryotes [PMID:20797862, PMID:12364329, PMID:27559127, PMID:20519582]. The complex is recruited to membranes through PI3P binding, Mon1 basic-patch electrostatic interactions, and a Ccz1 amphipathic helix that senses lipid packing defects; selective targeting to autophagosomes additionally requires a Ccz1 C-terminal LIR motif that binds Atg8/LC3 [PMID:24623720, PMID:29446751, PMID:36649906]. In metazoans, a third subunit, RMC1/Bulli, forms a trimeric complex that mediates membrane recruitment without altering the Mon1–Ccz1 catalytic core, as revealed by cryo-EM structures at near-atomic resolution [PMID:37155863, PMID:40864718]. CCZ1 is also an essential host factor for filovirus and SARS-CoV-2 endosomal trafficking, and impaired CCZ1–MON1A GEF activity in Alzheimer's disease models leads to defective autophagosome maturation and accumulation of pathological substrates [PMID:37880247, PMID:35198070]."},"prefetch_data":{"uniprot":{"accession":"P86791","full_name":"Vacuolar fusion protein CCZ1 homolog","aliases":[],"length_aa":482,"mass_kda":55.9,"function":"Acts in concert with MON1A, as a guanine exchange factor (GEF) for RAB7, promotes the exchange of GDP to GTP, converting it from an inactive GDP-bound form into an active GTP-bound form (PubMed:23084991)","subcellular_location":"Lysosome membrane","url":"https://www.uniprot.org/uniprotkb/P86791/entry"},"depmap":{"release":"DepMap","has_data":false,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CCZ1"},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CCZ1","total_profiled":1310},"omim":[{"mim_id":"620660","title":"CCZ1 HOMOLOG, VACUOLAR PROTEIN TRAFFICKING- AND BIOGENESIS-ASSOCIATED PROTEIN; CCZ1","url":"https://www.omim.org/entry/620660"},{"mim_id":"620267","title":"REGULATOR OF MON1-CCZ1; RMC1","url":"https://www.omim.org/entry/620267"},{"mim_id":"620266","title":"RAB7A-INTERACTING MON1-CCZ1 COMPLEX SUBUNIT 1; RIMOC1","url":"https://www.omim.org/entry/620266"},{"mim_id":"611464","title":"MON1 HOMOLOG A, SECRETORY TRAFFICKING-ASSOCIATED; MON1A","url":"https://www.omim.org/entry/611464"},{"mim_id":"608954","title":"MON1 HOMOLOG B, SECRETORY TRAFFICKING-ASSOCIATED; MON1B","url":"https://www.omim.org/entry/608954"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Vesicles","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CCZ1"},"hgnc":{"alias_symbol":["CGI-43","CCZ1A"],"prev_symbol":["C7orf28A"]},"alphafold":{"accession":"P86791","domains":[{"cath_id":"3.30.450.70","chopping":"16-184","consensus_level":"high","plddt":94.4431,"start":16,"end":184},{"cath_id":"3.30.450.30","chopping":"199-263_277-366","consensus_level":"high","plddt":92.3156,"start":199,"end":366},{"cath_id":"3.30.450","chopping":"375-474","consensus_level":"high","plddt":86.8175,"start":375,"end":474}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P86791","model_url":"https://alphafold.ebi.ac.uk/files/AF-P86791-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P86791-F1-predicted_aligned_error_v6.png","plddt_mean":88.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CCZ1","jax_strain_url":"https://www.jax.org/strain/search?query=CCZ1"},"sequence":{"accession":"P86791","fasta_url":"https://rest.uniprot.org/uniprotkb/P86791.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P86791/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P86791"}},"corpus_meta":[{"pmid":"20797862","id":"PMC_20797862","title":"The Mon1-Ccz1 complex is the GEF of the late endosomal Rab7 homolog Ypt7.","date":"2010","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/20797862","citation_count":317,"is_preprint":false},{"pmid":"24824487","id":"PMC_24824487","title":"Activation of the Rab7 GTPase by the MON1-CCZ1 Complex Is Essential for PVC-to-Vacuole Trafficking and Plant Growth in Arabidopsis.","date":"2014","source":"The Plant cell","url":"https://pubmed.ncbi.nlm.nih.gov/24824487","citation_count":178,"is_preprint":false},{"pmid":"27559127","id":"PMC_27559127","title":"The Ccz1-Mon1-Rab7 module and Rab5 control distinct steps of autophagy.","date":"2016","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/27559127","citation_count":166,"is_preprint":false},{"pmid":"29038162","id":"PMC_29038162","title":"Systematic Analysis of Human Cells Lacking ATG8 Proteins Uncovers Roles for GABARAPs and the CCZ1/MON1 Regulator C18orf8/RMC1 in Macroautophagic and Selective Autophagic Flux.","date":"2017","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/29038162","citation_count":104,"is_preprint":false},{"pmid":"12364329","id":"PMC_12364329","title":"The Ccz1-Mon1 protein complex is required for the late step of multiple vacuole delivery pathways.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12364329","citation_count":104,"is_preprint":false},{"pmid":"14662743","id":"PMC_14662743","title":"Yeast homotypic vacuole fusion requires the Ccz1-Mon1 complex during the tethering/docking stage.","date":"2003","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/14662743","citation_count":94,"is_preprint":false},{"pmid":"29446751","id":"PMC_29446751","title":"Molecular mechanism to target the endosomal Mon1-Ccz1 GEF complex to the pre-autophagosomal structure.","date":"2018","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/29446751","citation_count":77,"is_preprint":false},{"pmid":"24623720","id":"PMC_24623720","title":"Dynamic association of the PI3P-interacting Mon1-Ccz1 GEF with vacuoles is controlled through its phosphorylation by the type 1 casein kinase Yck3.","date":"2014","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/24623720","citation_count":50,"is_preprint":false},{"pmid":"11590240","id":"PMC_11590240","title":"The Ccz1 protein interacts with Ypt7 GTPase during fusion of multiple transport intermediates with the vacuole in S. cerevisiae.","date":"2001","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/11590240","citation_count":46,"is_preprint":false},{"pmid":"26627821","id":"PMC_26627821","title":"Mon1-Ccz1 activates Rab7 only on late endosomes and dissociates from the lysosome in mammalian cells.","date":"2015","source":"Journal of cell 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Neither protein alone has GEF activity; only the complex counteracts GAP function in vivo, rescues in vitro fusion of vacuoles carrying Ypt7-GDP, and promotes nucleotide exchange on Ypt7 independently of Vps39/HOPS.\",\n      \"method\": \"In vitro nucleotide exchange assay, in vivo GAP counteraction assay, in vitro vacuole fusion rescue assay\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted GEF activity in vitro with multiple orthogonal assays; foundational paper with 317 citations\",\n      \"pmids\": [\"20797862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Mon1 and Ccz1 physically interact as a stable protein complex (Ccz1-Mon1 complex) that peripherally associates with a perivacuolar compartment and vacuole membrane. The complex is required for the late fusion step in multiple vacuole delivery pathways (Cvt, autophagy, pexophagy, CPY, ALP, MVB pathways), functioning after vesicle formation but before or at fusion with the vacuole.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, fluorescence microscopy, genetic deletion analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus fractionation plus multiple pathway genetic analysis; 104 citations\",\n      \"pmids\": [\"12364329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The Ccz1-Mon1 complex binds the vacuole membrane and is required for the tethering/docking stage of homotypic vacuole fusion. In its absence, vacuole SNARE pairing and HOPS complex interaction are impaired. The complex colocalizes with other fusion components in the cis-SNARE complex, and its vacuole association is regulated by the class C Vps/HOPS complex.\",\n      \"method\": \"In vitro homotypic vacuole fusion assay, co-immunoprecipitation, fluorescence microscopy, biochemical fractionation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro fusion assay combined with Co-IP and localization; 94 citations\",\n      \"pmids\": [\"14662743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Ccz1 physically interacts with the Rab GTPase Ypt7. Extragenic suppressors of CCZ1 deletion are gain-of-function alleles of YPT7 with mutations in guanine-binding domains, and co-immunoprecipitation confirms direct physical interaction between Ccz1 and Ypt7.\",\n      \"method\": \"Extragenic suppressor screen, co-immunoprecipitation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis plus direct Co-IP; 46 citations\",\n      \"pmids\": [\"11590240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The Mon1-Ccz1 GEF complex is recruited to vacuoles via phosphatidylinositol 3-phosphate (PI3P). After activating Ypt7, Mon1 is phosphorylated by the type 1 casein kinase Yck3, which triggers Mon1 release from vacuoles for recycling. Mutation of Mon1 phosphorylation sites retains Mon1 on vacuoles.\",\n      \"method\": \"In vitro competition assay with PI3P, recombinant Yck3 phosphorylation assay, phosphosite mutagenesis, vacuole binding assays\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution of phosphorylation plus mutagenesis plus lipid binding competition; multiple orthogonal methods\",\n      \"pmids\": [\"24623720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In mammalian cells, Mon1-Ccz1 activates RAB7 specifically on late endosomes but dissociates from lysosomes. RAB7 activation on late endosomes by Mon1-Ccz1 is required for late endosome-lysosome fusion, whereas RAB7 activity on lysosomes is Mon1-Ccz1-independent and contributes to perinuclear lysosome clustering.\",\n      \"method\": \"FRET-based RAB7 activity sensor, confocal imaging, knockdown of Mon1-Ccz1\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — live-cell FRET sensor with spatial resolution and functional knockdown\",\n      \"pmids\": [\"26627821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In Drosophila, the Ccz1-Mon1-Rab7 module is required for autophagosome-lysosome fusion. Loss of Ccz1-Mon1-Rab7 causes autophagosome accumulation due to failed lysosomal fusion, whereas Rab5 is dispensable for Ccz1-Mon1-dependent Rab7 recruitment to PI3P-positive autophagosomes (generated by Atg14-containing Vps34 complex) during starvation.\",\n      \"method\": \"Genetic loss-of-function in Drosophila fat cells, fluorescence microscopy, epistasis analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined cellular phenotype and pathway epistasis; 166 citations\",\n      \"pmids\": [\"27559127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"C18orf8/RMC1 is a novel subunit of the CCZ1-MON1 RAB7 GEF complex in mammals that positively regulates RAB7 recruitment to late endosomes/autophagosomes. It was identified through interaction proteomics of proteins accumulating in GABARAP/L1/L2-deficient cells.\",\n      \"method\": \"Interaction proteomics (AP-MS), genetic KO of ATG8 subfamily members, quantitative proteomics of autophagosomes\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — interaction proteomics plus functional validation in KO cells; 104 citations\",\n      \"pmids\": [\"29038162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mon1-Ccz1 is specifically recruited to the pre-autophagosomal structure (PAS) during starvation through direct binding of at least one LIR motif in the Ccz1 C-terminus to Atg8 (yeast LC3 homolog). This LIR motif is essential for autophagy but dispensable for endosomal transport. Wild-type but not LIR-mutated Mon1-Ccz1 promotes Atg8-dependent activation of Ypt7.\",\n      \"method\": \"LIR motif mutagenesis, in vitro binding assays, autophagy and endosomal transport functional assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis with in vitro binding validation and separate functional readouts for two pathways; 77 citations\",\n      \"pmids\": [\"29446751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C5orf51 interacts with GDP-locked RAB7A and with MON1 and CCZ1 subunits of the RAB7 GEF complex. In the absence of C5orf51, RAB7A localization on depolarized mitochondria is compromised and RAB7A is degraded by the proteasome, impairing mitophagy. C5orf51 depletion also inhibits ATG9A recruitment to depolarized mitochondria.\",\n      \"method\": \"Proximity-dependent biotinylation (miniTurbo), genetic KO, mitophagy functional assays, proteasome inhibitor rescue\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — BioID proximity screen plus functional KO validation; 32 citations\",\n      \"pmids\": [\"34432599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The lysosomal V-ATPase a3 subunit interacts with the Mon1A-Ccz1 complex through the amino-terminal half domain of a3 and the longin motifs of Mon1A and Ccz1. This interaction localizes Mon1A-Ccz1 to secretory lysosomes in osteoclasts to mediate RAB7 recruitment, which is essential for bone resorption.\",\n      \"method\": \"Co-immunoprecipitation in HEK293T cells, domain mapping, osteoclast localization of endogenous Ccz1 in a3-KO cells\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP with domain mapping plus endogenous localization in KO cells\",\n      \"pmids\": [\"35589873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CCZ1 is an essential host factor for Marburg and Ebola filovirus infections, controlling early-to-late endosomal trafficking of these viruses. CCZ1 also contributes to endosomal trafficking of endocytosis-dependent SARS-CoV-2. Inhibition of CCZ1 nearly completely abolishes Marburg and Ebola infections in 3D primary human hepatocyte cultures and blood-vessel organoids.\",\n      \"method\": \"Haploid cell genetic screen, CCZ1 KO validation in 3D human organoids and cell lines, viral infection assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide screen plus validation in primary human tissue models with mechanistic specificity\",\n      \"pmids\": [\"37880247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structure of the metazoan Mon1-Ccz1-Bulli (MCBulli) complex was solved at 3.2 Å. Bulli associates as a leg-like extension at the periphery of the Mon1-Ccz1 heterodimer without impacting GEF activity or interactions with recruiter/substrate GTPases. Mon1 and Ccz1 constitute the active site of the complex. MCBulli shows structural homology to the Fuzzy-Inturned-Wdpcp (ciliogenesis) complex, but with divergent architecture suggesting Bulli serves as a recruitment platform for endolysosomal trafficking regulators.\",\n      \"method\": \"Cryo-electron microscopy at 3.2 Å resolution, structural comparison\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — near-atomic resolution cryo-EM structure with functional interpretation\",\n      \"pmids\": [\"37155863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"An amphipathic helix in Ccz1 is required for Mon1-Ccz1 function in autophagy but not endosomal maturation. Mon1 basic patches bind positively charged lipids, and the Ccz1 amphipathic helix interacts with lipid packing defects. A synergistic combination of protein-lipid interactions and recruiter protein associations governs differential targeting of Mon1-Ccz1 to endosomes versus autophagosomes. Membrane binding enhances MC1 GEF activity primarily by increasing enzyme-substrate concentration.\",\n      \"method\": \"Mutagenesis of amphipathic helix and Mon1 basic patches, lipid binding assays, in vitro GEF activity assays, autophagy and endosomal transport functional assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with in vitro lipid binding and GEF activity assays with separate pathway readouts\",\n      \"pmids\": [\"36649906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The CCZ1-MON1A complex activity as RAB7 GEF is impaired in Alzheimer's disease models, leading to reduced active RAB7 on autophagosomes and defective autophagosome maturation. Overexpression of CCZ1-MON1A increases active RAB7, enhances autophagosome maturation, and promotes degradation of APP-CTFs, Aβ and P-tau in an autophagy-dependent manner.\",\n      \"method\": \"GST-R7BD affinity-isolation assay for GTP-RAB7 on autophagosome fractions, AAV-mediated overexpression and knockdown in mouse brain, immunoblotting\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical assay of RAB7 activity on purified autophagosomes plus in vivo functional validation\",\n      \"pmids\": [\"35198070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Structural and functional comparison revealed that dimeric Mon1-Ccz1 from fungi and metazoan Mon1-Ccz1-RMC1/Bulli bind membranes through electrostatic interactions via distinct interfaces. RMC1/Bulli serves as an essential mediator of GEF complex membrane recruitment in metazoans. Both Mon1-Ccz1 and Fuzzy-Inturned complexes rely on a conserved sequence motif in their substrate GTPases for the catalytic mechanism, while secondary interactions provide target discrimination.\",\n      \"method\": \"Cryo-EM structure determination, protein-lipid interaction studies, in vitro reconstitution, functional characterization in Drosophila\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure combined with in vitro reconstitution and in vivo Drosophila functional validation\",\n      \"pmids\": [\"40864718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In C. elegans, CCZ-1 mediates digestion of apoptotic corpses by acting in lysosome biogenesis and phagosome maturation, recruiting the GTPase RAB-7 to phagosomes.\",\n      \"method\": \"Genetic loss-of-function in C. elegans, fluorescence microscopy of phagosome maturation markers\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined cellular phenotype and RAB-7 localization readout in C. elegans ortholog\",\n      \"pmids\": [\"20519582\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCZ1 forms an obligate heterodimeric (or trimeric with RMC1/Bulli in metazoans) guanine nucleotide exchange factor complex with MON1 that activates the late-endosomal Rab GTPase RAB7/Ypt7 on late endosomes and autophagosomes; the complex is recruited to membranes via PI3P binding, basic-patch electrostatic interactions, a Ccz1 amphipathic helix sensing lipid packing defects, and direct interaction with Atg8/LC3 through a Ccz1 LIR motif for autophagosomal targeting; after RAB7 activation, Mon1 is phosphorylated by casein kinase Yck3 and released for recycling; the metazoan third subunit RMC1/Bulli mediates membrane recruitment and serves as a platform for additional regulators; and the complex is essential for late endosome maturation, autophagosome-lysosome fusion, and multiple vacuole delivery pathways.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CCZ1 is an essential subunit of the Mon1–Ccz1 guanine nucleotide exchange factor (GEF) complex that activates the late-endosomal Rab GTPase RAB7/Ypt7 to drive endosome maturation, autophagosome–lysosome fusion, and phagosome maturation across eukaryotes [PMID:20797862, PMID:12364329, PMID:27559127, PMID:20519582]. The complex is recruited to membranes through PI3P binding, Mon1 basic-patch electrostatic interactions, and a Ccz1 amphipathic helix that senses lipid packing defects; selective targeting to autophagosomes additionally requires a Ccz1 C-terminal LIR motif that binds Atg8/LC3 [PMID:24623720, PMID:29446751, PMID:36649906]. In metazoans, a third subunit, RMC1/Bulli, forms a trimeric complex that mediates membrane recruitment without altering the Mon1–Ccz1 catalytic core, as revealed by cryo-EM structures at near-atomic resolution [PMID:37155863, PMID:40864718]. CCZ1 is also an essential host factor for filovirus and SARS-CoV-2 endosomal trafficking, and impaired CCZ1–MON1A GEF activity in Alzheimer's disease models leads to defective autophagosome maturation and accumulation of pathological substrates [PMID:37880247, PMID:35198070].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that Ccz1 physically and genetically interacts with the Rab GTPase Ypt7 placed Ccz1 upstream of Ypt7 in vacuolar trafficking before its enzymatic function was known.\",\n      \"evidence\": \"Extragenic suppressor screen yielding gain-of-function YPT7 alleles plus co-immunoprecipitation in yeast\",\n      \"pmids\": [\"11590240\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enzymatic mechanism unknown—whether Ccz1 acts as a GEF, effector, or scaffold was unresolved\", \"No in vitro nucleotide exchange data\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating that Mon1 and Ccz1 form a stable complex required for the fusion step in multiple vacuole delivery pathways (Cvt, autophagy, pexophagy, CPY, ALP, MVB) defined the obligate heterodimer and its broad pathway requirement.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, subcellular fractionation, and deletion analysis across six vacuolar pathways in yeast\",\n      \"pmids\": [\"12364329\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular activity of the complex (GEF, tether, or other) was uncharacterized\", \"How the complex is recruited to membranes was unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing that the Ccz1–Mon1 complex is required at the tethering/docking stage of homotypic vacuole fusion and that its membrane association depends on the HOPS complex resolved where in the fusion cascade it acts.\",\n      \"evidence\": \"In vitro homotypic vacuole fusion assay, SNARE pairing analysis, and HOPS-dependent membrane association in yeast\",\n      \"pmids\": [\"14662743\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct GEF activity had not been biochemically demonstrated\", \"Relationship between HOPS regulation and Ypt7 activation was unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Reconstituting Mon1–Ccz1 as the Ypt7 GEF in vitro answered the central mechanistic question: the complex directly catalyzes GDP-to-GTP exchange on Ypt7, independently of the HOPS subunit Vps39.\",\n      \"evidence\": \"In vitro nucleotide exchange assay, in vivo GAP counteraction, and vacuole fusion rescue with Ypt7-GDP in yeast\",\n      \"pmids\": [\"20797862\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for catalysis unknown\", \"Whether GEF activity is conserved in metazoans was untested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Parallel work in C. elegans demonstrated conserved function: CCZ-1 recruits RAB-7 to phagosomes for apoptotic corpse clearance, extending the GEF paradigm to phagosome maturation in metazoans.\",\n      \"evidence\": \"Genetic loss-of-function and fluorescence imaging of RAB-7 recruitment to phagosomes in C. elegans\",\n      \"pmids\": [\"20519582\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct GEF activity was not biochemically tested in the metazoan system\", \"Whether the phagosomal and endosomal functions are mechanistically identical was unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identifying PI3P as the membrane recruitment signal and Yck3-mediated phosphorylation of Mon1 as the release mechanism established the lipid-dependent recruitment cycle governing GEF complex dynamics on vacuoles.\",\n      \"evidence\": \"In vitro PI3P competition assay, recombinant Yck3 phosphorylation, phosphosite mutagenesis in yeast\",\n      \"pmids\": [\"24623720\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether metazoan Mon1–Ccz1 uses the same PI3P-dependent recruitment was untested\", \"No structural view of lipid interaction\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrating that mammalian Mon1–Ccz1 activates RAB7 specifically on late endosomes but not lysosomes showed spatial restriction of GEF activity, distinguishing endosome maturation from lysosome maintenance.\",\n      \"evidence\": \"FRET-based RAB7 activity sensor and knockdown in mammalian cells\",\n      \"pmids\": [\"26461827\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of spatial restriction (why Mon1–Ccz1 dissociates from lysosomes) was unknown\", \"Identity of lysosomal RAB7 GEF or stabilizer not established\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Genetic analysis in Drosophila proved that Ccz1–Mon1–Rab7 is essential for autophagosome–lysosome fusion and showed that PI3P generated by the Atg14-containing Vps34 complex—not Rab5—recruits the GEF, resolving the upstream signal for autophagy-specific targeting.\",\n      \"evidence\": \"Genetic knockout in Drosophila fat cells with epistasis between Atg14, Rab5, and Ccz1–Mon1–Rab7\",\n      \"pmids\": [\"27559127\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding of Ccz1 to autophagosomes was not molecularly defined\", \"Whether additional autophagy-specific recruiters exist was unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery of C18orf8/RMC1 as a third subunit of the metazoan complex revealed that the mammalian GEF is a heterotrimer, raising questions about how the additional subunit modulates function.\",\n      \"evidence\": \"Interaction proteomics (AP-MS) in GABARAP-family knockout cells\",\n      \"pmids\": [\"29038162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural role of RMC1 was undefined\", \"Whether RMC1 affects GEF catalytic activity was unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of a LIR motif in the Ccz1 C-terminus that directly binds Atg8 explained how Mon1–Ccz1 is selectively recruited to autophagosomes for autophagy-specific Ypt7 activation, while being dispensable for endosomal transport.\",\n      \"evidence\": \"LIR motif mutagenesis, in vitro Atg8 binding, and separate autophagy versus endosomal functional assays in yeast\",\n      \"pmids\": [\"29446751\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the LIR motif is conserved and functional in metazoan CCZ1 was untested\", \"Structural basis of LIR–Atg8 interaction was lacking\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Interaction mapping between the V-ATPase a3 subunit and the longin motifs of Mon1A and Ccz1 revealed a tissue-specific recruitment mechanism localizing the GEF to secretory lysosomes in osteoclasts for bone resorption.\",\n      \"evidence\": \"Co-immunoprecipitation with domain mapping in HEK293T cells and endogenous Ccz1 localization in a3-KO osteoclasts\",\n      \"pmids\": [\"35589873\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether a3–Mon1A–Ccz1 interaction is direct or scaffolded was not resolved with purified components\", \"Functional rescue of bone resorption by reconstituted complex was not shown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating that CCZ1 is an essential host factor for filovirus and endocytosis-dependent SARS-CoV-2 infection connected endosomal RAB7 activation to viral entry, establishing CCZ1 as a potential antiviral target.\",\n      \"evidence\": \"Haploid genetic screen validated by CCZ1 KO in 3D human hepatocyte cultures and blood-vessel organoids\",\n      \"pmids\": [\"37880247\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Precise step in viral trafficking controlled by CCZ1 (early-to-late endosome transition vs. membrane fusion) was not resolved\", \"Whether CCZ1 inhibition is therapeutically viable without disrupting normal endolysosomal trafficking was not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linking impaired CCZ1–MON1A GEF activity to defective autophagosome maturation in Alzheimer's disease models, with rescue by overexpression, established a disease-relevant consequence of reduced RAB7 activation on autophagosomes.\",\n      \"evidence\": \"GST-R7BD affinity isolation of GTP-RAB7 on purified autophagosomes, AAV-mediated expression in mouse brain\",\n      \"pmids\": [\"35198070\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal mechanism of CCZ1–MON1A impairment in AD was not identified\", \"Whether therapeutic augmentation of GEF activity is feasible in human neurons was untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The 3.2 Å cryo-EM structure of the metazoan Mon1–Ccz1–Bulli trimer showed that Bulli forms a peripheral leg-like extension without contacting the GEF active site, establishing it as a recruitment platform rather than a catalytic modulator.\",\n      \"evidence\": \"Cryo-EM at 3.2 Å resolution with structural comparison to the Fuzzy–Inturned–Wdpcp ciliogenesis complex\",\n      \"pmids\": [\"37155863\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the complex bound to Rab7 substrate was not captured\", \"How Bulli recruits specific regulators was structurally uncharacterized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Dissecting the Ccz1 amphipathic helix and Mon1 basic patches revealed a synergistic lipid-sensing mechanism that differentially targets the complex to endosomes versus autophagosomes, with membrane binding enhancing GEF activity by concentrating enzyme and substrate.\",\n      \"evidence\": \"Mutagenesis of amphipathic helix and basic patches combined with in vitro lipid binding and GEF assays, plus separate autophagy and endosomal functional readouts in yeast\",\n      \"pmids\": [\"36649906\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural visualization of the amphipathic helix inserted into membranes was not achieved\", \"Whether the same lipid-sensing logic operates in metazoan cells was not directly tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Comparative cryo-EM and functional analysis confirmed that RMC1/Bulli mediates membrane recruitment through electrostatic interfaces distinct from the fungal dimer, and identified a conserved GTPase sequence motif recognized by both Mon1–Ccz1 and the structurally related Fuzzy–Inturned complex, unifying the catalytic mechanism across Rab and Rsg1 substrates.\",\n      \"evidence\": \"Cryo-EM structures, protein-lipid interaction assays, in vitro reconstitution, and Drosophila functional validation\",\n      \"pmids\": [\"40864718\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transition-state structure of the GEF–Rab7 catalytic intermediate is still missing\", \"How target discrimination is achieved at the single-residue level beyond the conserved motif remains unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: the transition-state structure of Mon1–Ccz1 bound to nucleotide-free Rab7; the identity and regulation of upstream signals that inactivate or degrade the complex in metazoans; and whether pharmacological modulation of CCZ1-dependent GEF activity can be achieved for antiviral or neurodegenerative disease applications.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No transition-state GEF–Rab7 complex structure\", \"Metazoan recycling mechanism (analogous to Yck3 phosphorylation) not identified\", \"No pharmacological tools to modulate Mon1–Ccz1 activity\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 5, 6, 14]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [4, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1, 2, 5, 11]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [5, 10, 16]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 6, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 2, 5, 11]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [6, 8, 13, 14]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [5, 10, 16]}\n    ],\n    \"complexes\": [\n      \"Mon1-Ccz1 (heterodimer)\",\n      \"Mon1-Ccz1-RMC1/Bulli (metazoan heterotrimer)\"\n    ],\n    \"partners\": [\n      \"MON1A\",\n      \"MON1B\",\n      \"YPT7\",\n      \"RAB7A\",\n      \"RMC1\",\n      \"ATG8\",\n      \"ATP6V0A3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}