Guanine nucleotide exchange factor (GEF) for RAB5A and RAB22A that activates RAB5A and RAB22A by exchanging bound GDP for free GTP. Plays a role in endocytosis via its role in activating Rab family members. Interacts with RAB5A, RAB22A and MUSK. Detected in thymus and spleen (at protein level). Detected in lung, liver, kidney, spleen, thymus and skeletal muscle. Truncated N-terminus. Truncated N-terminus.