TRAPPC10

TRAPPC10 is a TRAPPII complex-specific subunit that confers Rab GTPase exchange factor (GEF) substrate selectivity, directing the TRAPP catalytic core toward Rab11 (Ypt31/32 in yeast) at the late Golgi to coordinate intra-Golgi trafficking, endosome-to-Golgi recycling, lipid droplet homeostasis, and autophagy (PMID:17041589, PMID:16314430, PMID:28003315, PMID:23078654). Cryo-EM structures show that TRAPPC10 provides a 'leg' domain that positions the active site distal to the membrane, sterically gating against Rab1 and enabling selective Rab11 activation, while the mammalian TRAPPII complex also activates Rab1 and Rab18 in biochemical assays (PMID:35559680, PMID:34229011, PMID:28003315). TRAPPC10 assembles into TRAPPII through TRAPPC9 (bridged by TRAPPC2) and TRAPPC2L, and loss of TRAPPC10 destabilizes TRAPPC9 and impairs membrane trafficking (PMID:21858081, PMID:35298461, PMID:30120216). Biallelic loss-of-function variants in TRAPPC10 cause a microcephalic neurodevelopmental disorder, confirmed by patient cell rescue experiments and Trappc10-knockout mice displaying microcephaly and neuroanatomical defects (PMID:35298461).

1. 2002 Medium

   Genetic suppressor analysis first positioned Trs130 (TRAPPC10 ortholog) in the Ypt31/32 (Rab11) trafficking pathway by showing that high-copy YPT31/32 suppresses TRS130 deletion lethality and that TRS130 genetically interacts with ARF1, establishing TRAPPC10 as a regulator upstream of Rab11-family GTPases.

   Evidence Synthetic lethal screen and high-copy suppressor analysis in budding yeast

   PMID:12210902

   Open questions at the time

   • Genetic placement did not demonstrate direct GEF activity
   • Mammalian relevance not yet addressed
   • Mechanism of Trs130 action unknown
2. 2005 High

   Demonstration that Trs130 is required for vesicle traffic from the early endosome to the late Golgi established the specific trafficking step controlled by this subunit, with electron microscopy revealing aberrant membrane accumulation in trs130 mutants.

   Evidence Temperature-sensitive mutant analysis, electron microscopy, fluorescence colocalization, and secretion assays in yeast

   PMID:16314430

   Open questions at the time

   • Whether Trs130 directly acts on Rab GTPases remained untested
   • No structural information on how Trs130 contributes to TRAPPII function
3. 2006 High

   The key mechanistic insight that TRAPPII-specific subunits including Trs130 switch the TRAPP complex's GEF specificity from Ypt1 (Rab1) to Ypt31/32 (Rab11) resolved how a shared catalytic core can serve two distinct Rab substrates at different Golgi compartments.

   Evidence GEF activity assays and genetic epistasis in budding yeast

   PMID:17041589

   Open questions at the time

   • Structural basis for specificity switching unknown
   • Mammalian TRAPPII Rab specificity not yet tested
4. 2009 High

   Extension to mammalian cells showed that TRAPPC10 is a component of mammalian TRAPPII enriched on COPI-coated vesicles, that the complex activates Rab1, and that TRAPPC10 depletion causes vesicle accumulation and cargo mistargeting near the Golgi, translating the yeast findings to mammalian Golgi trafficking.

   Evidence shRNA knockdown, co-immunoprecipitation, immunoelectron microscopy, and GEF assays in mammalian cells

   PMID:19656848

   Open questions at the time

   • Mammalian TRAPPII Rab11 GEF activity not yet demonstrated
   • COPI interaction mechanism not structurally resolved
5. 2011 Medium

   Mapping the intra-complex assembly revealed that TRAPPC2 acts as an adaptor bridging TRAPPC9 to the TRAPP core, and TRAPPC9 in turn binds TRAPPC10, explaining how disease-causing mutations in TRAPPC2 or TRAPPC9 disrupt TRAPPII assembly.

   Evidence Co-immunoprecipitation with wild-type and disease-mutant constructs in mammalian cells

   PMID:21858081

   Open questions at the time

   • Single-lab Co-IP study without reciprocal or structural validation of the TRAPPC9–TRAPPC10 interface
   • Stoichiometry of the complex not determined
6. 2012 Medium

   Refined genetic epistasis confirmed that Trs130 functions specifically in the Ypt31/32 (not Ypt1) pathway, and further showed that TRAPPII/Trs130 participates in autophagy by regulating Atg8/Atg9 transport to the pre-autophagosomal structure downstream of Atg5 and upstream of Atg1.

   Evidence Temperature-sensitive mutant analysis, GFP-Snc1 and GFP-Atg8/Atg9 transport assays, Ape1 maturation, and genetic suppression in yeast

   PMID:22426882 PMID:23078654

   Open questions at the time

   • Mammalian autophagy role of TRAPPC10 not tested
   • Molecular mechanism linking Rab activation to autophagosome biogenesis unclear
7. 2016 High

   Discovery that mammalian TRAPPII acts as a GEF for Rab18 and that TRAPPII-specific subunit loss causes aberrantly large lipid droplets expanded the functional repertoire of TRAPPC10-containing TRAPPII beyond Golgi trafficking to lipid droplet homeostasis.

   Evidence siRNA depletion, CRISPR-Cas9 knockout, GEF assays, live-cell imaging, and lipid droplet phenotype analysis in mammalian cells

   PMID:28003315

   Open questions at the time

   • Whether TRAPPC10 directly contacts Rab18 or only positions the catalytic core unknown
   • Physiological significance of lipid droplet defect in vivo not established
8. 2018 Medium

   Identification of a TRAPPC2L disease variant that ablates interaction with TRAPPC10 and leads to increased active RAB11 in patient cells provided the first human genetic evidence that the TRAPPC2L–TRAPPC10 interaction regulates RAB11 activation state.

   Evidence Yeast two-hybrid, patient fibroblast studies, RAB11 activation measurement

   PMID:30120216

   Open questions at the time

   • Single-family study; mechanism by which loss of TRAPPC2L–TRAPPC10 interaction increases active RAB11 is counterintuitive and not fully explained
   • No structural data on TRAPPC2L–TRAPPC10 interface
9. 2021 High

   Comprehensive biochemical profiling established that mammalian TRAPPII containing TRAPPC10 has GEF activity toward Rab1 and Rab11 (but not 18 other Rabs) and that membrane association enhances activity with conformational changes, resolving the mammalian Rab specificity profile.

   Evidence GEF assays against 20 Rabs, hydrogen-deuterium exchange mass spectrometry, electron microscopy, and membrane-reconstituted assays

   PMID:34229011

   Open questions at the time

   • Discrepancy with earlier Rab18 GEF activity claim not fully reconciled
   • Membrane-induced conformational changes not mapped to specific subunits
10. 2022 High

    Cryo-EM structures of the TRAPPII–Rab11 complex revealed the structural basis for substrate selectivity: TRAPPC10's 'leg' domain elevates the catalytic core from the membrane surface, sterically excluding Rab1 and permitting Rab11 access, while Trs120 acts as a 'lid' enclosing the active site.

    Evidence Cryo-EM structure determination of the 22-subunit yeast TRAPPII complex including a Rab11 exchange intermediate

    PMID:35559680

    Open questions at the time

    • Mammalian TRAPPII structure not yet solved
    • Dynamic conformational gating during catalysis not captured
11. 2022 High

    Biallelic TRAPPC10 loss-of-function variants were shown to cause microcephalic neurodevelopmental disorder, with loss of TRAPPC10 destabilizing TRAPPC9, disrupting membrane trafficking, and producing microcephaly in knockout mice — establishing TRAPPC10 as a disease gene.

    Evidence Patient lymphoblastoid cells, knockout cell lines, Co-IP, trafficking assays, rescue with wild-type vs. mutant constructs, and Trappc10−/− mouse model

    PMID:35298461

    Open questions at the time

    • Specific neuronal cell types and developmental stages most affected not determined
    • Whether trafficking defect or specific Rab dysregulation underlies neuronal pathology unclear
12. 2024 Medium

    Demonstration that TRAPPC6B loss reduces TRAPPC9 and TRAPPC10 protein levels, and that TRAPPC6B co-precipitates preferentially with TRAPPII, further defined TRAPPC10 as specifically enriched in the TRAPPII complex and showed upstream dependencies for its stability.

    Evidence Patient fibroblast protein analysis, co-immunoprecipitation, Golgi trafficking rescue assay

    PMID:37713627

    Open questions at the time

    • Mechanism by which TRAPPC6B stabilizes TRAPPII-specific subunits is unclear
    • Whether TRAPPC6B loss phenocopies TRAPPC10 loss in neurons not tested

• Key unresolved questions include the high-resolution structure of mammalian TRAPPII, the reconciliation of conflicting Rab18 GEF data, the specific neuronal mechanisms underlying TRAPPC10-associated microcephaly, and whether TRAPPC10 has functions independent of the TRAPPII complex.
• No mammalian TRAPPII cryo-EM structure
• Rab18 vs. Rab11 GEF specificity discrepancy across studies unresolved
• Cell-type-specific roles in brain development not dissected