Biologically active conformer of the effector region of human C5a and modulatory effects of N-terminal receptor binding determinants on activity.
A conformationally biased decapeptide agonist of human C5a (C5a55-74Y65,F67,P69,P71,D-Ala73 or YSFKPMPLaR) was used as a functional probe of the C5a receptor (C5aR) in order to understand the conformational features in the C-terminal effector region of C5a that are important for C5aR binding and signal transduction. YSFKPMPLaR was a potent, full agonist of C5a, but at higher concentrations had a superefficacious effect compared to the natural factor. The maximal efficacy of this analogue was 216 +/- 56% that of C5a in stimulating the release of beta-glucuronidase from human neutrophils. C5aR activation and binding curves both occurred in the same concentration range with YSFKPMPLaR, characteristics not observed with natural C5a or more conformationally flexible C-terminal agonists. YSFKPMPLaR was then used as a C-terminal effector template onto which was synthesized various C5aR binding determinants from the N-terminal core domain of the natural factor. In general, the presence of N-terminal binding determinants had little effect on either potency or binding affinity when the C-terminal effector region was presented to the C5aR in this biologically active conformation. However, one peptide, C5a12-20-Ahx-YSFKPMPLaR, expressed a 100-fold increase in affinity for the neutrophil C5aR and a 6-fold increase in potency relative to YSFKPMPLaR. These analyses showed that the peptides used in this study have up to 25% of the potency of C5a in human fetal artery and up to 5% of the activity of C5a in the PMN enzyme release assay.
Finch
A M
AM
Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Australia.
Vogen
S M
SM
Sherman
S A
SA
Kirnarsky
L
L
Taylor
S M
SM
Sanderson
S D
SD
D015703:Antigens, CD / Q000378:metabolism*; D001158:Arteries / Q000187:drug effects / Q000196:embryology; D001667:Binding, Competitive; D015936:Complement C5a / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D005333:Fetus; D005966:Glucuronidase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000196:embryology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D044087:Receptor, Anaphylatoxin C5a; D011951:Receptors, Complement / Q000378:metabolism*; D014661:Vasoconstriction / Q000187:drug effects
D015703:Antigens, CD; D010446:Peptide Fragments; D044087:Receptor, Anaphylatoxin C5a; D011951:Receptors, Complement; C105322:complement C5a, (65-74), Tyr(65)-Phe(67)-Pro(69,71)-Ala(73)-; D015936:Complement C5a; D005966:Glucuronidase