RhoGAP_myosin_IX: RhoGAP (GTPase-activator protein [GAP] for Rho-like small GTPases) domain present in class IX myosins. Class IX myosins contain a characteristic head domain, a neck domain, a tail domain which contains a C6H2-zinc binding motif and a RhoGAP domain. Class IX myosins are single-headed, processive myosins that are partly cytoplasmic, and partly associated with membranes and the actin cytoskeleton. Class IX myosins are implicated in the regulation of neuronal morphogenesis and function of sensory systems, like the inner ear. There are two major isoforms, myosin IXA and IXB with several splice variants, which are both expressed in developing neurons. 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.
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