Vesicle trafficking protein that functions in the early secretory pathway, possibly by mediating retrograde transport from cis-Golgi membranes to the ER. Part of the SNARE core complex containing STX7, VAMP8 and VTI1B. Interacts with VAMP8. Forms a SNARE complex with STX7, VTI1B 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 HECTD3 (By similarity). Interacts with TPC1 (By similarity). Preferentially associated with the early endosome. To a lesser extent, also present in late endosome, the plasma membrane and coated pits. Widely expressed in all tissues examined. Ubiquitinated by HECTD3. Belongs to the syntaxin family.