Ras-related protein Rab-27A, also known as RAB27A, belongs to the small GTPase superfamily, Rab family. The protein is membrane-bound and may be involved in protein transport and small GTPase mediated signal transduction. Also, RAB27A regulates the cytotoxic granule exocytosis and affect T-lymphocyte and macrophage-activation. It is widely expressed with significant expression in pancreatic islets and pituitary tissue, and low expression in brain. Defects in RAB27A cause Griscelli syndrome type 2 (GS2).