Turn Structures in CGRP C-Terminal Analogues Promote Stable Arrangements of Key Residue Side Chains
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- 作者：Katharine A. Carpenter ; Ralf Schmidt ; Bengt von Mentzer ; Ulla Haglund ; Edward Roberts ; and Chris Walpole
- 刊名：Biochemistry
- 出版年：2001
- 出版时间：July 17, 2001
- 年：2001
- 卷：40
- 期：28
- 页码：8317 - 8325
- 全文大小：125K
- 年卷期：v.40,no.28(July 17, 2001)
- ISSN：1520-4995
文摘
The 37-amino acid calcitonin gene-related peptide (CGRP) is a potent endogenous vasodilatorthought to be implicated in the genesis of migraine attack. CGRP antagonists may thus have therapeuticvalue for the treatment of migraine. The CGRP C-terminally derived peptide [D31,P34,F35]CGRP(27-37)-NH2 was recently identified as a high-affinity hCGRP1 receptor selective antagonist. Reasonable CGRP1affinity has also been demonstrated for several related analogues, including [D31,A34,F35]CGRP(27-37)-NH2. In the study presented here, conformational and structural features in CGRP(27-37)-NH2 analoguesthat are important for hCGRP1 receptor binding were explored. Structure-activity studies carried out on[D31,P34,F35]CGRP(27-37)-NH2 resulted in [D31,P34,F35]CGRP(30-37)-NH2, the shortest reported CGRPC-terminal peptide analogue exhibiting reasonable hCGRP1 receptor affinity (Ki = 29.6 nM). Furtherremoval of T30 from the peptide's N-terminus greatly reduced receptor affinity from the nanomolar tomicromolar range. Additional residues deemed critical for hCGRP1 receptor binding were identified froman alanine scan of [A34,F35]CGRP(28-37)-NH2 and included V32 and F37. Replacement of the C-terminalamide in this same peptide with a carboxyl, furthermore, resulted in a greater than 50-fold reduction inhCGRP1 affinity, thus suggesting a direct role for the amide moiety in receptor binding. The conformationalproperties of two classes of CGRP(27-37)-NH2 peptides, [D31,X34,F35]CGRP(27-37)-NH2 (X is A orP), were examined by NMR spectroscopy and molecular modeling. A 
-turn centered on P29 was a notablefeature consistently observed among active peptides in both series. This turn led to exposure of the criticalT30 residue to the surrounding environment. Peptides in the A34 series were additionally characterized bya stable C-terminal helical turn that resulted in the three important residues (T30, V32, and F37) adoptingconsistent interspatial positions with respect to one another. Peptides in the P34 series were comparativelymore flexible at the C-terminus, although a large proportion of the [D31,P34,F35]CGRP(27-37)-NH2calculated conformers contained a 
-turn centered on P34. These results collectively suggest that turnstructures at both the C-terminus and N-terminus of CGRP(27-37)-NH2 analogues may help toappropriately orient critical residues (T30, V32, and F37) for hCGRP1 receptor binding.
-turn centered on P29 was a notablefeature consistently observed among active peptides in both series. This turn led to exposure of the criticalT30 residue to the surrounding environment. Peptides in the A34 series were additionally characterized bya stable C-terminal helical turn that resulted in the three important residues (T30, V32, and F37) adoptingconsistent interspatial positions with respect to one another. Peptides in the P34 series were comparativelymore flexible at the C-terminus, although a large proportion of the [D31,P34,F35]CGRP(27-37)-NH2calculated conformers contained a -turn centered on P34. These results collectively suggest that turnstructures at both the C-terminus and N-terminus of CGRP(27-37)-NH2 analogues may help toappropriately orient critical residues (T30, V32, and F37) for hCGRP1 receptor binding.