May act as a RAB27A effector protein and play a role in cytotoxic granule exocytosis in lymphocytes. Monomer. Binds NRXN1. Binds RAB27A that has been activated by GTP-binding via its N-terminus. Interacts with RAB27B (By similarity). In the pancreatic alpha cells distributed in both peripheral and anterior regions. Localizes on the glucagon granules in the cell periphery. The RabBD domain mediates interaction with RAB27A.