Differential activities of decapeptide agonists of human C5a: the conformational effects of backbone N-methylation

Analogues of the potent, conformationally biased, decapeptide agonist of hu man C5a anaphylatoxin, C5a(65-74)Y65,F67,P69,P71,D-Ala73 (YSFKPMPLaR, pepti de 54), were synthesized with methyl groups occupying specific C5a,, amide nitrogen atoms along the peptide backbone. This N-methylation induced cruci al extended backbone conformations in a manner similar to the two Pro resid ues, but without eliminating the contributions made by the side-chain of th e residue for which Pro was substituted. The presence of backbone N-methyl groups on peptide 54 analogues had pronounced detrimental effects on the ab ility to bind and activate C5aRs expressed on human PMNs, but not on the ab ility to contract smooth muscle of human umbilical artery. Several N-methyl ated analogues of peptide 54 (peptides 56, 67, 124, 125, and 137) were sign ificantly more selective for smooth muscle contraction, which is mediated b y tissue resident macrophages, than for enzyme release from PMNs. Indeed, p eptide 67, YSFKDMP(MeL)aR was almost 3000-fold more selective for smooth mu scle contraction than for PMN enzyme release. Consistent with these differe ntial activities was the observation that peptide 67 expressed a significan tly greater binding affinity to C5aRs expressed on rat macrophages than on rat PMNs. This differential activity was also observed in vivo in the rat w here peptide 67 induced a hypotensive response similar to peptide 54 and rh uC5a, but without accompanying neutropenia. (C) 2001 Elsevier Science B.V. All rights reserved.