The Bin/Amphiphysin/Rvs (BAR) domain of Rich-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 GAP interacting with CIP4 homologs proteins (Rich). Members contain an N-terminal BAR domain, followed by a Rho GAP domain, and a C-terminal prolin-rich region. Vertebrates harbor at least three Rho GAPs in this subfamily including Rich1, Rich2, and SH3-domain binding protein 1 (SH3BP1). Rich1 and Rich2 play complementary roles in the establishment and maintenance of cell polarity. Rich1 is a Cdc42- and Rac-specific GAP that binds to polarity proteins through the scaffold protein angiomotin and plays a role in maintaining the integrity of tight junctions. Rich2 is a Rac GAP that interacts with CD317 and plays a role in actin cytoskeleton organization and the maintenance of microvilli in polarized epithelial cells. SH3BP1 is a Rac GAP that inhibits Rac-mediated platelet-derived growth factor (PDGF)-induced membrane ruffling. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions. The BAR domain of Rich1 has been shown to form oligomers, bind membranes and induce membrane tubulation.