Peptide inhibitors of E. collagenolyticum bacterial collagenase--effect of N-methylation. Consequences on biological activity and conformational properties.

Peptide inhibitors of E. collagenolyticum bacterial collagenase, HS-CH2-CH2-CO-Pro-Yaa (Yaa = Ala, Leu, Nle), have been N-methylated at the Yaa position. The N-methylation slightly increases the inhibitory potency of the modified peptides as compared to the parent compounds. The conformational effects of the N-methylation have been investigated by both 1H 2D-NMR and molecular mechanics energy minimization. Three low-energy conformers have been predicted for the unmethylated parent compounds (Yaa = Ala, Leu, Nle). They are characterized by the psi value of the central proline residue: psi Pro = 150 degrees (trans' conformation), psi Pro = 70 degrees (C7 conformation) and psi Pro = -50 degrees (cis' conformation). The N-methylation has been found to strongly increase the energy of the C7 conformer and to a less extent the energy of the cis' conformer. This leaves the trans' conformation as the only low-energy conformer. The ROESY experiments have established that both the N-methyl peptides and the parent compounds adopt the same preferred backbone conformation in water solution, i.e. the trans' conformation. Based on these results, the activities of the N-methyl peptides are discussed and a possible conformation of the inhibitor in the bound state is proposed.