Acts as a guanine nucleotide exchange factor (GEF) for Rab5 GTPase. Regulates the ALS2-mediated endosome dynamics (By similarity). Homodimer. Forms a heteromeric complex with ALS2. Interacts with ALS2 and RAB5A. Distributed onto the vesicular compartments in the cytoplasm with strong punctated staining. Colocalizes with RAB5A onto the vesicular/membranous compartments in the cytoplasm, particularly to the leading edges of the cells (By similarity). Expressed in heart, lung, liver and kidney. Extended N-terminus. Intron retention.