Syntaxin-binding protein 2 (Munc-18) is involved in intracellular vesicle trafficking and vesicle fusion with membranes. Munc-18 contributes to the granule exocytosis machinery through interaction with soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins that regulate membrane fusion. Munc-18 regulates cytotoxic granule exocytosis in natural killer (NK) cells. The function of Munc-18 is regulated by PKC phosphorylation of Ser515.