Decapeptide agonists of human C5a: the relationship between conformation and neutrophil response

Abstract

A series of decapeptide analogues corresponding to the C-terminal region of the human C5a anaphylatoxin (C5a65-74) was synthesized with residue substitutions to restrict conformational flexibility in the C-terminal region (residues 71-74). These analogues behaved as full agonists of natural C5a in their ability to induce shape change (polarization) and the release of enzyme (beta-glucuronidase) from human neutrophils (PMNs). There was a significant pharmacological correlation between the polarization and enzyme-release assays, suggesting similarities in PMN responsiveness toward these constrained peptides. Good correlations were also observed between these two PMN responses and spasmogenic activity (smooth muscle contraction of human fetal artery). A structure-function analysis for PMN polarization and enzyme release led to the identification of the following preferred backbone conformations: a twisted, helix-like conformation for residues 65-69, an extended conformation for residues 70-71, and a beta-turn of type V for residues (71)72-74. The existence of a C-terminal, type V beta-turn is supported by the NOE (nuclear Overhauser effect) results of two peptides from this series. These conformational features are reminiscent of those that were shown to correlate with the expression of spasmogenic and platelet aggregatory activities in an earlier investigation (Sanderson, S.D.; et al. J. Med. Chem. 1994, 37, 3171). These results suggest that PMNs and the cells responsible for smooth muscle contraction possess C5a receptors that respond to similar topochemical features presented by the agonist peptide ligand.

Potent Cyclic Antagonists of the Complement C5a Receptor on Human Polymorphonuclear Leukocytes. Relationships between Structures and Activity

“…Small peptides derived from the C terminus of C5a typically show partial agonist activity in promoting enzyme release from human PMNLs (Luly et al, 1993;Konteatis et al, 1994Konteatis et al, , 1997Siciliano et al, 1994;Sanderson et al, 1995;Finch et al, 1997). Decapeptide YSFKPMPLaR is one of the most potent examples of a full agonist, with an apparent receptor affinity for human PMNLs of 5 M (Finch et al, 1997).…”

“…The solution structure of C5a (Zuiderweg et al, 1989;Zhang et al, 1997) consists of a 64-residue, high-affinity 'receptor-binding' N-terminal helix bundle attached to a 10-residue low affinity 'receptor-activating' C-terminal domain thought to bind in a transmembrane pore region of the receptor Huber-Lang et al, 2003). Much effort has been devoted to developing short peptides derived from the C terminus of C5a as agonists/antagonists (Drapeau et al, 1993;Luly et al, 1993;Konteatis et al, 1994;Sanderson et al, 1994Sanderson et al, , 1995Finch et al, 1997). Most were partial agonists, but the hexapeptide MeFKPdChaWr was a full antagonist with Ͻ1 M affinity for the C5aR (Drapeau et al, 1993;Konteatis et al, 1994).…”

Development of Response-Selective Agonists of Human C5a Anaphylatoxin Conformational, Biological, and Therapeutic Considerations

“…This same panel of conformationally biased agonists was evaluated in assays measuring the ability of these agonists to induce the release of β-glucuronidase from human PMNs and the polarization (shape change) of PMNs [43]. YSFKDMPLaR behaved as a potent full agonist in the PMN assays (EC 50 = 2.1 µM for polarization and 57.7 µM for enzyme release), but it was not the most potent member of this panel as it was in the spasmogenic and platelet aggregatory assays.…”

Induction of an Antigen-Specific CTL Response by a Conformationally Biased Agonist of Human C5a Anaphylatoxin as a Molecular Adjuvant

“…pD 2 transforms [Ϫlog EC 50 (M)] were calculated for each concentration-response curve and reported as the mean Ϯ SE. Peptide binding affinity to the C5aR was evaluated on intact human PMNs by a competition assay using [ 125 I]-C5a according to previously described methods (7,8). Statistical analysis of the values obtained from pharmacologic assays was performed using one-way ANOVA.…”