Component of the BLOC-1 complex, a complex that is required for normal biogenesis of lysosome-related organelles (LRO), such as platelet dense granules and melanosomes. In concert with the AP-3 complex, the BLOC-1 complex is required to target membrane protein cargos into vesicles assembled at cell bodies for delivery into neurites and nerve terminals. The BLOC-1 complex, in association with SNARE proteins, is also proposed to be involved in neurite extension. Plays a role in intracellular vesicle trafficking and synaptic vesicle recycling. May modulate a step between vesicle priming, fusion and calcium-dependent neurotransmitter release through its ability to potentiate the interaction of synaptotagmin with the SNAREs and the plasma-membrane-associated protein SNAP25. Its phosphorylation state influences exocytotic protein interactions and may regulate synaptic vesicle exocytosis. May also have a role in the mechanisms of SNARE-mediated membrane fusion in non-neuronal cells (PubMed:17182842, PubMed:18167355). As part of the BORC complex may play a role in lysosomes movement and localization at the cell periphery. Associated with the cytosolic face of lysosomes, the BORC complex may recruit ARL8B and couple lysosomes to microtubule plus-end-directed kinesin motor (PubMed:25898167). Component of the biogenesis of lysosome-related organelles complex 1 (BLOC-1) composed of BLOC1S1, BLOC1S2, BLOC1S3, BLOC1S4, BLOC1S5, BLOC1S6, DTNBP1/BLOC1S7 and SNAPIN/BLOC1S8. Octamer composed of one copy each BLOC1S1, BLOC1S2, BLOC1S3, BLOC1S4, BLOC1S5, BLOC1S6, DTNBP1/BLOC1S7 and SNAPIN/BLOC1S8. The BLOC-1 complex associates with the AP-3 protein complex and membrane protein cargos (PubMed:15102850, PubMed:22203680). Component of the BLOC-one-related complex (BORC) which is composed of BLOC1S1, BLOC1S2, BORCS5, BORCS6, BORCS7, BORCS8, KXD1 and SNAPIN (PubMed:25898167). Associates with the SNARE complex. Interacts with CSNK1D, SNAP23 and STX4A but not with STX1A, VAMP2 and SYT1. Interacts with SNAP25; the interaction with SNAP25 is increased by its phosphorylation. Interacts with CNTRL, NANOS1, PUM2 and RGS7 (PubMed:12659861, PubMed:16213214, PubMed:19168546). Interacts with TOR1A; the interaction is direct and associates SNAPIN with the CSN complex (PubMed:18167355, PubMed:21102408). (Microbial infection) Interacts with human cytomegalovirus/HHV-5 protein UL70. Colocalizes with NANOS1 and PUM2 in the perinuclear region of germ cells. Expressed in male germ cells of adult testis (at protein level). Expressed in germ cells of 22-week prenatal testis. Phosphorylated by CSNK1D/CK1 (By similarity). Phosphorylated by PKD, phosphorylation controls SNAPIN protein stability. Belongs to the SNAPIN family.