VPS29 (Q9UBQ0) Curation Notes

Overview & Dual Complex Membership (Retromer & Retriever/Commander)

• VPS29 (Q9UBQ0, ~20.5 kDa, 182 aa) is a compact subunit with a calcineurin-like metallophosphoesterase (MPE) fold that serves as an essential structural scaffold and regulatory hub in two distinct endosomal cargo-recycling complexes:
• Retromer Cargo-Selective Complex (CSC) (VPS35:VPS29:VPS26A or VPS35:VPS29:VPS26B), where the C-terminal alpha-solenoid of VPS35 wraps around VPS29 (PMID:11102511; [PMID:17891154, "Here we report the crystal structure of a VPS29-VPS35 subcomplex showing how the metallophosphoesterase-fold subunit VPS29 (refs 14, 15) acts as a scaffold for the carboxy-terminal half of VPS35."]; PMID:37172566).
• Retriever Complex (VPS26C:VPS35L:VPS29), a heterotrimer composed of VPS26C (DSCR3), VPS35L (C16orf62), and VPS29 that assembles with the 10-subunit CCC complex (COMMD1–10, CCDC22, CCDC93) and DENND10 to form the 16-subunit Commander supercomplex (GO:0160309, commander complex) ([PMID:28892079, "We have called this complex 'retriever'; it is a heterotrimer composed of DSCR3, C16orf62 and VPS29, and bears striking similarity to retromer."]; PMID:34943955; [PMID:37172566, "Retriever, a VPS26C:VPS35L:VPS29 trimer, shares distant homology to Retromer, itself a trimer of VPS29, VPS35, and either VPS26A or VPS26B (paralogues with VPS26C)."]).

Pseudoenzyme Status: Complete Lack of Phosphatase Activity

• Although VPS29 adopts a classic calcineurin-like metallophosphoesterase fold capable of coordinating divalent metal cations in vitro, VPS29 is a catalytically inactive pseudoenzyme:
• In the Q9UBQ0 sequence (SQ, residues 61–65 GDFDE, immediately adjacent to the divalent metal-coordinating Asp62), position 63 is a conserved phenylalanine (Phe63) rather than a catalytic histidine (file:human/VPS29/VPS29-uniprot.txt).
• Furthermore, when VPS29 is assembled into the retromer CSC (or Retriever), the putative metal-binding cleft is sterically occluded by the C-terminal alpha-solenoid of VPS35 (or VPS35L) ([PMID:17891154, "VPS35 forms a horseshoe-shaped, right-handed, alpha-helical solenoid, the concave face of which completely covers the metal-binding site of VPS29"]; PMID:37172566).
• UniProt Q9UBQ0 explicitly records in CC -!- CAUTION (lines 401–404, citing RN [9] and RN [14] Swarbrick et al., "VPS29 is not an active metallo-phosphatase but is a rigid scaffold required for retromer interaction with accessory proteins."): "CAUTION: Was originally believed to be a metal-dependent phosphatase but shown to lack catalytic activity; can bind metals with very low affinity suggesting that metal binding is not required for its function." (file:human/VPS29/VPS29-uniprot.txt).
• Therefore, any phosphoprotein phosphatase activity (GO:0004721) or hydrolase activity (GO:0016787) annotations inferred from the MPE fold or early in vitro assays would be false; notably, human GOA has already removed those MF terms, leaving GO:0140312 (cargo adaptor activity, contributes_to via IBA) and GO:0005515 (protein binding).

Core Biological Functions

1. Structural Scaffold of Retromer CSC and Retriever:
2. Stabilizes the C-terminal domain of VPS35 in retromer (PMID:17891154) and the C-terminal domain of VPS35L in Retriever/Commander (PMID:28892079; PMID:37172566).
3. Regulatory Hub for Endosomal Rab7 Cycling (TBC1D5) and Tubular Scission (VARP, SNX1/2):
4. Presents a conserved hydrophobic surface patch (centered on Leu152) opposite the VPS35-binding interface that directly recruits the Rab7 GTPase-activating protein TBC1D5 (PMID:20923837; [PMID:24603492, "The RabGAP protein TBC1D5 controls cellular endomembrane trafficking processes and binds the retromer subunit VPS29 and the ubiquitin-like protein ATG8 (LC3)."]), the Rab21/VAMP7-interacting adaptor VARP (ANKRD27), and the bacterial effector RidL (from Legionella pneumophila).
5. By recruiting TBC1D5, VPS29 promotes GTP hydrolysis on RAB7A to drive timely retromer coat disassembly and coordinate endosomal tubule dynamics (PMID:20923837).
6. Inside the 16-subunit Commander complex, the C-terminal tail of VPS35L wraps across the Leu152 hydrophobic pocket of VPS29, sterically blocking TBC1D5 and VARP binding so that Retriever does not recruit retromer-specific accessory factors (PMID:37172566).
7. Endosome-to-TGN Retrieval (GO:0042147) and Endocytic Recycling (GO:0032456):
8. Essential as part of retromer for endosome-to-TGN retrieval of CI-MPR (IGF2R), sortilin (SORT1), and Wntless (WLS) (PMID:15078903; PMID:18193037; PMID:20923837) and for SNX27-retromer endocytic recycling (PMID:21602791).
9. Essential as part of Retriever (coupled to SNX17 and the CCC complex) for retromer-independent endosome-to-plasma membrane recycling of over 120 cell-surface cargoes carrying NPxY/NxxY motifs, including alpha5-beta1 integrin (ITGA5/ITGB1), LRP1, and LDLR (PMID:28892079; PMID:34943955; PMID:37172566).

Key Curation & GO Annotation Decisions

• Core MF (ACCEPT and REMOVE):
• GO:0140312 (cargo adaptor activity, contributes_to, IBA GO_REF:0000033): ACCEPT — VPS29 scaffolds the C-terminal alpha-solenoid of VPS35 (and VPS35L) and recruits TBC1D5/VARP to contribute to retromer and retriever cargo adaptor activity; represented under contributes_to_molecular_function in both core_functions entries (for GO:0030906 retromer, cargo-selective complex and GO:0160309 commander complex).
• GO:0005515 (protein binding): All 39 unique IPI entries in existing_annotations (corresponding to 40 raw GO:0005515 IPI rows in VPS29-goa.tsv, where rows 19 and 68 are duplicate IntAct/UniProtKB:Q9UBQ0 self-interaction rows) are REMOVE per standard GO protein-binding policy.
• Core BP (ACCEPT and MODIFY):
• GO:0042147 (retrograde transport, endosome to Golgi, IBA, IEA, and NAS PMID:26220253): ACCEPT.
• GO:0032456 (endocytic recycling, IMP PMID:28892079, NAS PMID:30072228, NAS PMID:34943955): ACCEPT.
• NOT|involved_in GO:0010506 (regulation of autophagy, IMP PMID:24603492, negated: true): ACCEPT — PMID:24603492 shows that TBC1D5 and the AP2 complex regulate the rerouting of ATG9-containing vesicular carriers toward sites of autophagosome formation via clathrin/AP2 and the active ULK1 complex, and the GO curator recorded a NOT|involved_in assertion for VPS29.
• Core CC (ACCEPT, MODIFY, NEW, and REMOVE):
• GO:0030906 (retromer, cargo-selective complex, IDA PMID:27385586, IPI PMID:11102511, NAS PMID:26220253) and GO:0030904 (retromer complex, IBA, IDA PMID:11102511, IDA PMID:28892079, IEA): ACCEPT.
• GO:0032991 (protein-containing complex, IDA PMID:28892079 and IDA PMID:37172566): MODIFY to GO:0160309 (commander complex).
• GO:0005768 (endosome), GO:0005769 (early endosome), GO:0010008 (endosome membrane), and GO:0005829 (cytosol): ACCEPT.
• GO:0097422 (tubular endosome, IDA PMID:15078903): Proposed as NEW because PMID:15078903 demonstrates that human VPS26, VPS29, and VPS35 colocalize on tubular early endosomal domains (already annotated on VPS26A and VPS35 from the same paper).
• GO:0005737 (cytoplasm) and GO:0016020 (membrane): MODIFY to GO:0005829 (cytosol) and GO:0010008 (endosome membrane).
• GO:0005770 (late endosome, IEA GO_REF:0000044): KEEP_AS_NON_CORE — retromer remains associated with maturing early-to-late endosomes during Rab7/TBC1D5 recruitment.
• GO:0005789 (endoplasmic reticulum membrane, NAS PMID:34943955): REMOVE with source_defects (WRONG_TERM -> GO:0010008 endosome membrane) — spurious ComplexPortal NAS annotation from an endosomal Commander review article.