Binds phosphatidylinositol 3,4,5-trisphosphate (By similarity). May play a role in vesicle trafficking. Acts as a RAB27A effector protein and may play a role in cytotoxic granule exocytosis in lymphocytes. Monomer. Binds NCF2 and NRXN1 (By similarity). Binds RAB27A that has been activated by GTP-binding via its N-terminus. Highly expressed in lung. Detected at lower levels in spleen, liver and kidney, and at very low levels in heart, brain and skeletal muscle. Expressed in cytotoxic T-lymphocytes (CTL).