Involved in intracellular vesicle trafficking. Identified in a complex containing STX6, STX12 and VAMP4 (By similarity). This complex also includes VTI1A (PubMed:9705316). Binds EEA1 (By similarity). Interacts with VPS45A and GOPC (By similarity). Interacts with MARCHF2; the interaction promotes MARCHF2-mediated ubiquitination and degradation of CFTR (By similarity). Interacts with MARCHF3 (By similarity). Interacts with UHRF1BP1L (via C-terminal coiled-coil domain) (By similarity). Interacts with BAIAP3; this interaction is increased in the presence of calcium (By similarity). Belongs to the syntaxin family.