{"uniprot":"Q587I9","gene":"SFT2D3","name":"Vesicle transport protein SFT2C","organism":"Homo sapiens (Human)","status":"dark","length":215,"sequence":"MADLHRQLQEYLAQGKAGGPAAAEPLLAAEKAEEPGDRPAEEWLGRAGLRWTWARSPAESAAAGLTCLPSVTRGQRLAAGGGCLLLAALCFGLAALYAPVLLLRARKFALLWSLGSALALAGSALLRGGAACGRLLRCEEAPSRPALLYMAALGATLFAALGLRSTLLTVLGAGAQVAALLAALVGLLPWGGGTALRLALGRLGRGAGLAKVLPV","function_summary":"A multi-pass membrane trafficking factor that assembles within Golgi membranes to organize retrograde flow from endosomes. By providing a membrane-embedded scaffold for binding other trafficking proteins, it coordinates vesicle tethering and fusion that retrieve sorting receptors and lipids back to the Golgi, thereby sustaining endosome-to-Golgi transport and Golgi-endosome homeostasis.","plain_language":"SFT2D3 has barely been studied. The model's best guess: A multi-pass membrane trafficking factor that assembles within Golgi membranes to organize retrograde flow from endosomes. By providing a membrane-embedded scaffold for binding other trafficking proteins, it coordinates vesicle tethering and fusion that retrieve sorting receptors and lipids back to the Golgi, thereby sustaining endosome-to-Golgi transport and Golgi-endosome homeostasis.","uniprot_summary":"Involved in endosome-to-Golgi trafficking.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0042147","label":"retrograde transport, endosome to Golgi"}],"cellular_component":[{"id":"GO:0005794","label":"Golgi apparatus"}]},"interpro":[{"id":"IPR011691","name":"Vesicle transport protein SFT2","type":"family","start":55,"end":197},{"id":"IPR007305","name":"Vesicle transport protein, Got1/SFT2-like","type":"family","start":79,"end":189}],"reasoning":"I begin with the InterPro architecture. The core of the protein is defined by IPR011691 (Vesicle transport protein SFT2 family, residues 55–197) and an overlapping family signature IPR007305 (Vesicle transport protein, Got1/SFT2-like family, residues 79–189). This tandem of SFT2/Got1-like family domains concentrated in the central-to-C-terminal region indicates a compact, multi-pass membrane module specialized for vesicle trafficking rather than enzymatic catalysis. SFT2/Got1-like proteins are small-to-medium Golgi/endosome trafficking factors that assemble via helical bundles into oligomeric scaffolds. The absence of catalytic motifs and the dominance of trafficking-family signatures causally point to a role as a membrane-embedded adaptor that binds other proteins to choreograph vesicle tethering and fusion.\n\nFrom this architecture, the molecular function resolves as protein binding (GO:0005515). SFT2/Got1-like modules create multivalent interfaces within membranes, capturing partner proteins that mediate vesicle docking and fusion. Their membrane-embedded helices and luminal/cytosolic loops provide the physical basis for selective protein–protein interactions that regulate trafficking pathways.\n\nThis binding-driven mechanism naturally feeds into retrograde transport from endosomes to the Golgi apparatus (GO:0042147). The SFT2/Got1-like scaffold stabilizes and times the retrieval pathway that returns sorting receptors and lipids from endosomes back to the Golgi. By organizing tethering and fusion machinery at the Golgi–endosome interface, the protein directly sustains endosome-to-Golgi retrograde flow.\n\nCellular localization follows from both the domain family and the membrane-embedded nature of the scaffold. The SFT2 family is canonically Golgi-associated, and a multi-pass topology anchors the protein as an integral component of membrane. This positioning aligns with a residence at the Golgi apparatus (GO:0005794), where retrograde vesicles are received and processed. The membrane annotation and multi-pass architecture together specify a stable Golgi localization with potential cycling to endosome-derived carriers.\n\nMechanistically, I hypothesize that the protein forms a membrane-integrated tethering hub that binds other trafficking factors to coordinate SNARE pairing and vesicle fusion at the Golgi. Likely partners include Golgi-localized SNAREs and tethering complexes that operate on endosome-derived carriers. By stabilizing these assemblies, the protein ensures efficient cargo retrieval and maintains Golgi-endosome homeostasis.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q587I9.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q587I9"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q587I9/entry","atlas":"/p/Q587I9"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}