Involved in intracellular vesicle trafficking. Identified in a complex containing STX6, STX12, VAMP4 and VTI1A. Binds EEA1. Interacts with VPS45A and GOPC. 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). Interacts with BAIAP3; this interaction is increased in the presence of calcium (By similarity). Belongs to the syntaxin family.