γ-SNAP stimulates disassembly of endosomal SNARE complexes and regulates endocytic trafficking pathways

Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) that reside in the target membranes and transport vesicles assemble into specific SNARE complexes to drive membrane fusion. N-ethylmaleimide-sensitive factor (NSF) and its attachment protein, alpha-SNAP (encoded by NAPA), catalyze disassembly of the SNARE complexes in the secretory and endocytic pathways to recycle them for the next round of fusion events. gamma-SNAP (encoded by NAPG) is a SNAP isoform, but its function in SNARE-mediated membrane trafficking remains unknown. Here, we show that gamma-SNAP regulates the endosomal trafficking of epidermal growth factor (EGF) receptor (EGFR) and transferrin. Immunoprecipitation and mass spectrometry analyses revealed that gamma-SNAP interacts with a limited range of SNAREs, including endosomal ones. gamma-SNAP, as well as alpha-SNAP, mediated the disassembly of endosomal syntaxin-7-containing SNARE complexes. Overexpression and small interfering (si) RNA-mediated depletion of gamma-SNAP changed the morphologies and intracellular distributions of endosomes. Moreover, the depletion partially suppressed the exit of EGFR and transferrin from EEA1-positive early endosomes to delay their degradation and uptake. Taken together, our findings suggest that gamma-SNAP is a unique SNAP that functions in a limited range of organelles - including endosomes and their trafficking pathways.