 Rheb is a 21-kDa protein monomer composed of 184 amino acids.The first 169 amino acids by the N-terminus make up the GTPase domain, and the remaining amino acids are part of a hypervariable region ending at the C-terminus in a CAAX motif (C – cysteine, A – aliphatic amino acid, X – C-terminus amino acid).The protein is a lipid-anchored, cell-membrane protein with five repeats of the RAS-related GTP-binding region.