 The GRD is closely homologous to RasGAP and represents about 10% (229 amino acids) of the neurofibromin sequence.The GRD is made up of a central portion called the minimal central catalytic domain (GAPc) as well as an extra domain (GAPex) that is formed through the coiling of about 50 residues from the N- and C- terminus.The Ras-binding region is found in the surface of GAPc and consists of a shallow pocket that is lined by conserved amino acid residues.