May play a role in vesicle trafficking (By similarity). Binds phosphatidylinositol 3,4,5-trisphosphate. Acts as a RAB27A effector protein and may play a role in cytotoxic granule exocytosis in lymphocytes (By similarity). Monomer. Binds NRXN1. Binds RAB27A that has been activated by GTP-binding via its N-terminus (By similarity). Binds NCF2. Peripheral membrane protein tightly bound to the cytoplasmic side of cellular membranes. Highly expressed in bone marrow and lymphoid tissues. Detected at lower levels in cerebellum, occipital lobe, prostate, stomach, kidney, appendix, lung and trachea. Expressed in cytotoxic T-lymphocytes (CTL).