First Step Toward the Quantitative Identification of Peptide 310-Helix Conformation with NMR Spectroscopy:  NMR and X-ray Diffraction Structural Analysis of a Fully-Developed 310-Helical Peptide Standard

We have synthesized by solution methods and fully characterized the Nα-blocked heptapeptide methylamide mBrBz-[L-Iva-L-(αMe)Val]2-L-(αMe)Phe-L-(αMe)Val-L-Iva-NHMe, fully based on conformationally constrained C α-methylated α-amino acids. An X-ray diffraction investigation of the N α-benzyloxycarbony...

Full description

Saved in:
Bibliographic Details
Published in:Journal of the American Chemical Society 1998-05, Vol.120 (19), p.4763-4770
Main Authors: Gratias, Rainer, Konat, Robert, Kessler, Horst, Crisma, Marco, Valle, Giovanni, Polese, Alessandra, Formaggio, Fernando, Toniolo, Claudio, Broxterman, Quirinus B, Kamphuis, Johan
Format: Article
Language:English
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:We have synthesized by solution methods and fully characterized the Nα-blocked heptapeptide methylamide mBrBz-[L-Iva-L-(αMe)Val]2-L-(αMe)Phe-L-(αMe)Val-L-Iva-NHMe, fully based on conformationally constrained C α-methylated α-amino acids. An X-ray diffraction investigation of the N α-benzyloxycarbonylated analogue showed that in the crystal state both independent molecules (A and B) in the asymmetric unit of the peptide adopt a fully developed, regular, right-handed 310-helical structure, although molecule A would be slightly distorted at the C-terminal residue. Solution conformational analysis on the mBrBz-blocked peptide was carried out in CDCl3 by means of NMR spectroscopy. For structure determination we performed restrained molecular dynamics simulations in CDCl3 based on a search of the conformational space derived from a simulated annealing strategy. For this peptide the NMR observables can be described by a single backbone conformation, more specifically a rigid 310-helix spanning the amino acid sequence from residue 1 to residue 6. The C-terminal methylamido NH group seems to be involved simultaneously in two H-bonds (with the preceding i − 3 and i − 4 carbonyl groups). Although in this peptide model there are no distinct NOE distances for discriminating 310- versus α-helix conformation, the sum of all NMR-derived restraints clearly results in a 310-helical structure. Convergence from different starting structures (including an α-helix) into a 310-helix was observed.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja9731478