RhoGAP_ARHGAP18: RhoGAP (GTPase-activator protein [GAP] for Rho-like small GTPases) domain of ArhGAP18-like proteins. The function of ArhGAP18 is unknown. Small GTPases cluster into distinct families, and all act as molecular switches, active in their GTP-bound form but inactive when GDP-bound. The Rho family of GTPases activates effectors involved in a wide variety of developmental processes, including regulation of cytoskeleton formation, cell proliferation and the JNK signaling pathway. GTPases generally have a low intrinsic GTPase hydrolytic activity but there are family-specific groups of GAPs that enhance the rate of GTP hydrolysis by several orders of magnitude.