Bioactive beta-bend structures for the antagonist halpha CGRP(8 - 37) at the CGRP(1) receptor of the rat pulmonary artery.
The aim of this study was to determine beta-bend structures and the role of the N- and C-terminus in the antagonist halpha CGRP(8 - 37) at the rat pulmonary artery CGRP receptor mediating halpha CGRP relaxation. Halpha CGRP(8 - 37) Pro(16) (10(-6) M), with a bend-biasing residue (proline) at position 16, did not antagonize halpha CGRP responses, while a structure-conserving amino acid (alanine(16)) at the same position retained antagonist activity (apparent pK(B) 6.6+/-0.1; 10(-6) M). Halpha CGRP(8 - 37) Pro(19) (10(-6) M), with proline at position 19 was an antagonist (apparent pK(B) 6.9+/-0.1). Incorporation of a beta-bend forcing residue, BTD (beta-turn dipeptide), at positions 19 and 20 in halpha CGRP(8 - 37) (10(-6) M) antagonized halpha CGRP responses (apparent pK(B) 7.2+/-0.2); and BTD at positions 19,20 and 33,34 within halpha CGRP(8 - 37) was a competitive antagonist (pA(2) 7.2; Schild plot slope 1.0+/-0.1). Halpha CGRP(8 - 37) analogues, substituted at the N-terminus by either glycine(8) or des-NH(2) valine(8) or proline(8) were all antagonists (apparent pK(B) 6.9+/-0.1; (10(-6) M), 7.0+/-0.1 (10(-6) M), and pA(2) 7.0 (slope 1.0+/-0.2), respectively); while replacements by proline(8) together with glutamic acid(10,14) in halpha CGRP(8 - 37) (10(-6) M) or alanine amide(37) at the C-terminus of halpha CGRP(8 - 37) (10(-5) M) were both inactive compounds. In conclusion, possible bioactive structures of halpha CGRP(8 - 37) include two beta-bends (at 18 - 21 and 32 - 35), which were mimicked by BTD incorporation. Within halpha CGRP(8 - 37), the N-terminus is not essential for antagonism while the C-terminus may interact directly with CGRP(1) receptors in the rat pulmonary artery.
Wisskirchen
F M
FM
Department of Pharmacology, University College London, Gower Street, London WC1E 6BT.
Doyle
P M
PM
Gough
S L
SL
Harris
C J
CJ
Marshall
I
I
D000409:Alanine / Q000737:chemistry; D019943:Amino Acid Substitution; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000737:chemistry* / Q000494:pharmacology*; D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D018698:Glutamic Acid / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D066298:In Vitro Techniques; D008297:Male; D008968:Molecular Conformation; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D010446:Peptide Fragments / Q000737:chemistry* / Q000494:pharmacology*; D011392:Proline / Q000737:chemistry; D011651:Pulmonary Artery / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D010446:Peptide Fragments; C058636:calcitonin gene-related peptide (8-37); D018698:Glutamic Acid; D011392:Proline; D015740:Calcitonin Gene-Related Peptide; D000409:Alanine; D005998:Glycine