Rab11 binding domain of Rab-3A-interacting protein (RAB3IP), Rab-3A-interacting-like protein 1 (RAB3IL1) and similar proteins
The family includes RAB3IP and RAB3IL1, as well as Rab guanine nucleotide exchange factor SEC2 from yeast. RAB3IP, also called Rabin-3, or SSX2-interacting protein, or Rabin8, acts as a guanine nucleotide exchange factor (GEF) which promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form. It mediates the release of GDP from RAB8A and RAB8B but not from RAB3A or RAB5. It modulates actin organization and promotes polarized transport of RAB8A-specific vesicles to the cell surface. RAB3IL1, also called guanine nucleotide exchange factor for Rab-3A (GRAB), or Rab3A-interacting-like protein 1, or Rabin3-like 1, acts as a guanine nucleotide exchange factor (GEF) which promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form. As a dual Rab-binding protein, RAB3IL1 could potentially link Rab3 and Rab11 and/or Rab8 and Rab11-mediated intracellular trafficking processes. It may activate RAB3A, a GTPase that regulates synaptic vesicle exocytosis. It may also activate RAB8A and RAB8B. In addition, RAB3IL1 interacts with InsP6K1 and plays a role for InsP7 in vesicle exocytosis. SEC2 is a guanine nucleotide exchange factor for SEC4, catalyzing the dissociation of GDP from SEC4 and also potently promoting binding of GTP. Activation of SEC4 by SEC2 is needed for the directed transport of vesicles to sites of exocytosis. SEC2 binds the Rab GTPase YPT32 but does not have exchange activity on YPT32. The model corresponds to the Rab11a/Rab11b-binding region of family members which lies within the carboxy-terminus, a region distinct from their GEF domain and Rab3a-binding region.