Plays a role in vesicle-mediated protein trafficking to lysosomal compartments including the endocytic membrane transport and autophagic pathways. Believed to act in part as a component of the putative HOPS endosomal tethering complex which is proposed to be involved in the rab-5-to-rab-7 endosome conversion probably implicating sand-1, and via binding SNAREs and SNARE complexes to mediate tethering and docking events during SNARE-mediated membrane fusion. The HOPS complex is proposed to be recruited to rab-7 on the late endosomal membrane and to regulate late endocytic, phagocytic and autophagic traffic towards lysosomes. Involved in homotypic vesicle fusions between late endosomes and in heterotypic fusions between late endosomes and lysosomes. Required for fusion of endosomes. In association with lgg-2 mediates the tethering of autophagosomes with lysosomes to form autolysosomes. Within the HOPS complex, contributes to the normal development of gut granules in embryonic and adult intestinal cells