May be involved in protein trafficking from the plasma membrane to the early endosome (EE) as well as in homotypic fusion of endocytic organelles. Mediates the endocytic trafficking from early endosomes to late endosomes and lysosomes (By similarity). Interacts with VPS11, VPS16 and VPS18. Interacts with VPS33A (By similarity). Forms a SNARE complex with VTI1B, STX8 and VAMP8 which functions in the homotypic fusion of late endosomes. Component of the SNARE complex composed of STX7, STX8, VAMP7 and VTI1B that is required for heterotypic fusion of late endosomes with lysosomes. Interacts with TPC1 (By similarity). Detected in all tissues tested. Highest expression is found in kidney followed by lung, spleen, heart and brain. Lower expression, in skeletal muscle, liver and testis. Belongs to the syntaxin family.