Inter-Residue Coupling of Model PPII Helices using 13c Isotopic Labeling

Abstract

Characterization of poly-proline II (PPII) conformation on a site-specific basis has importance in developing a model for structure and stability in these systems. Coupling of selected residues for a series of related peptides having predominantly PPII conformations were measured using VCD and IR spectra of selected variants that were doubly labeled with 13C on the amide C=O. The characteristics of the 13C=O component of the amide I’IR band and their sensitivity to the local structure of the peptide are compared to predictions based on DFT level calculations for related structures and used to determine coupling between C=O groups along the backbone of this helical structure.