Conformation of a novel tetrapeptide inhibitor NH2-d-Trp-d-Met-Phe(pCl)-Gla-NH2 bound to farnesyl-protein transferase

: Farnesyl‐protein transferase (FPTase) catalyzes the post‐translational farnesylation of the cysteine residue located in the C‐terminal tetrapeptide of the Ras oncoprotein. Prenylation of this residue is essential for membrane association and cell‐transforming activities of ras. Inhibitors of FPTase have been demonstrated to display antitumor activity in both tissue culture and animal models, and thus represent a potential therapeutic strategy for the treatment of human cancers. A synthetic tetrapeptide library, which included an expanded set of 68 l‐, d‐ and noncoded amino acids, has been screened for inhibitors of FPTase activity. The tetrapeptide, NH2‐d‐Trp‐d‐Met‐l‐Phe(pCl)‐l‐Gla‐NH2 was shown to be competitive with the isoprenyl cosubstrate, farnesyl diphosphate (FPP) but not with the peptide substrate, the C‐terminal tetrapeptide of the Ras protein. The FPTase‐bound conformation of the inhibitor, NH2‐d‐Trp‐d‐Met‐l‐Phe(pCl)‐l‐Gla‐NH2 was determined by NMR spectroscopy. Distance constraints were derived from two‐dimensional transferred nuclear Overhauser effect (TRNOE) experiments. Ligand competition experiments identified the NOEs that originate from the active‐site conformation of the inhibitor. Structures were calculated using a combination of distance geometry and restrained energy minimization. The peptide backbone is shown to adopt a reverse‐turn conformation most closely approximating a type II′β‐turn. The resolved conformation of the inhibitor represents a distinctly different structural motif from that determined for Ras‐competitive inhibitors. Knowledge of the bound conformation of this novel inhibitor provides a template and future direction for the design of new classes of FPTase antagonists.