The Bin/Amphiphysin/Rvs (BAR) domain of Oligophrenin1-like Rho GTPase Activating Proteins
BAR domains are dimerization, lipid binding and curvature sensing modules found in many different proteins with diverse functions. This subfamily is composed of Rho and Rac GTPase activating proteins (GAPs) with similarity to oligophrenin1 (OPHN1). Members contain an N-terminal BAR domain, followed by a Pleckstrin homology (PH) domain, and a Rho GAP domain. Some members contain a C-terminal SH3 domain. Vertebrates harbor at least three Rho GAPs in this subfamily including OPHN1, GTPase Regulator Associated with Focal adhesion kinase (GRAF), GRAF2, and an uncharacterized protein called GAP10-like. OPHN1, GRAF and GRAF2 show GAP activity towards RhoA and Cdc42. In addition, OPHN1 is active towards Rac. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions. The BAR domains of OPHN1 and GRAF directly interact with their Rho GAP domains and inhibit their activity. The autoinhibited proteins are able to bind membranes and tubulate liposomes, showing that the membrane-tubulation and GAP-inhibitory functions of the BAR domains can occur simultaneously.