The SNAREs vti1a and vti1b have distinct localization and SNARE complex partners

Two mammalian proteins, vti1a and vti1b, are homologous to the yeast Q-SNARE Vti1p which is part of several SNARE complexes in different transport steps. In vitro experiments suggest distinct functions for vti1a and vti1b. Here we compared the subcellular localization of endogenous vti1a and vti1b by immunofluorescence and immuno-electron microscopy. Both proteins had a distinct but overlapping localization. vti1a was found predominantly on the Golgi and the TGN, vti1b mostly on tubules and vesicles in the TGN area and on endosomes. vti1a coimmunoprecipitated with VAMP-4, syntaxin 6, and syntaxin 16. These four SNAREs could assemble into a SNARE complex of conserved structure because one SNARE motif of each subgroup is present. vtila-beta, VAMP-4, syntaxin 6, and syntaxin 16 are coenriched with small synaptic vesicles and with clathrin-coated vesicles isolated from rat brain synaptosomes. Therefore, this SNARE complex may have a role in synaptic vesicle biogenesis or recycling.