Guanine nucleotide exchange factor (GEF) which may activate RAB8A, RAB13 and RAB35. Promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form. Exhibits low nucleotide-independent RAB35-binding activity. Interacts with clathrin heavy chain/CLTC and with AP2A2, but not with AP2B1.