ENDOBREVIN, A NOVEL SYNAPTOBREVIN VAMP-LIKE PROTEIN PREFERENTIALLY ASSOCIATED WITH THE EARLY ENDOSOME/

Synaptobrevins /vesicle-associated membrane proteins (VAMPs) together with syntaxins and a synaptosome-associated protein of 25 kDa (SNAP-25 ) are the main components of a protein complex involved in the docking and/or fusion of synaptic vesicles with the presynaptic membrane. We report here the molecular, biochemical, and cell biological characteri zation of a novel member of the synaptobrevin/VAMP family. The amino a cid sequence of endobrevin has 32, 33, and 31% identity to those of sy naptobrevin/VAMP-1, synaptobrevin/VAMP-2, and cellubrevin, respectivel y. Membrane fractionation studies demonstrate that endobrevin is enric hed in membrane fractions that are also enriched in the asialoglycopro tein receptor. Indirect immunofluorescence microscopy establishes that endobrevin is primarily associated with the perinuclear vesicular str uctures of the early endocytic compartment. The preferential associati on of endobrevin with the early endosome was further established by el ectron microscopy (EM) immunogold labeling. In vitro binding assays sh ow that endobrevin interacts with immobilized recombinant alpha-SNAP f used to glutathione S-transferase (GST). Our results highlight the gen eral importance of members of the synaptobrevin/VAMP protein family in membrane traffic and provide new avenues for future functional and me chanistic studies of this protein as well as the endocytotic pathway.