Rab effector protein involved in melanosome transport. Serves as link between melanosome-bound RAB27A and the motor protein MYO5A. Binds RAB27A that has been activated by GTP-binding via its N-terminus. Binds MYO5A via its C-terminal coiled coil domain. Highly expressed in embryos at day 7; not detectable at day 11. Highly expressed in adult stomach; detected at lower levels in kidney, lung, skin and small intestine. Detected in melanocytes.