ARHGEF9 (Rho guanine nucleotide exchange factor 9, also called PEM2 or collybistin) selectively activates Cdc42 by exchanging bound GDP for free GTP []. It is highly expressed in the brain and it interacts with gephyrin, a postsynaptic protein associated with GABA and glycine receptors. Mutations in the ARHGEF9 gene cause X-linked mental retardation with associated features like seizures, hyper-anxiety, aggressive behavior, and sensory hyperarousal [, , ]. ARHGEF9 contains a SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains [].This entry represents the SH3 domain of ARHGEF9.
