Bioactive β-bend structures for the antagonist hα CGRP_(8-37) at the CGRP_1 receptor of the rat pulmonary artery

摘要

1. The aim of this study was to determine β-bend structures and the role of the N- and C-terminus in the antagonist hα CGRP_(8-37) at the rat pulmonary artery CGRP receptor mediating hα CGRP relaxation. 2. Hα CGRP_(8-37) Pro~(16) (10~(-6) M), with a bend-biasing residue (proline) at position 16, did not antagonize hα 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). Hα CGRP_(8-37) Pro~(19) (10~(-6) M), with proline at position 19 was an antagonist (apparent pK_B 6.9 ± 0.1). 3. Incorporation of a β-bend forcing residue, BTD (beta-turn dipeptide), at positions 19 and 20 in hα CGRP_(8-37) (10~(-6) M) antagonized hα CGRP responses (apparent pK_B 7.2 ± 0.2); and BTD at positions 19,20 and 33,34 within hα CGRP_(8-37) was a competitive antagonist (pA_2 7.2; Schild plot slope 1.0 ± 0.1). 4. Hα 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 hα CGRP_(8-37) (10~(-6)M) or alanine amide~(37) at the C-terminus of hα CGRP_(8-37) (10~(-5) M) were both inactive compounds. 5. In conclusion, possible bioactive structures of hα CGRP_(8-37) include two β-bends (at 18-21 and 32-35), which were mimicked by BTD incorporation. Within hα 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.