Vibrational Circular Dichroism of beta-Hairpin Peptides

Analysis of vibrational absorption and vibrational circular dichroism (VCD) for synthetic peptides designed to adopt beta-hairpin conformations reveals characteristic well-resolved amide I absorption and VCD bands. All beta-hairpins with a type II’ beta-turn segment yield an intense negative VCD band in the _1643-1659 cm-1 region, and a weak positive VCD band at _1693 cm-1. These spectral features are diagnostic of beta-hairpins and distinct from those observed for other secondary structures. Comparison of the electronic CD spectra of the beta-hairpin peptides Boc-Leu-Val-Val-DPro-Gly-Leu-Val-Val-OMe (1) and Boc-Leu-Phe-Val-DPro-Gly-Leu-Phe-Val-OMe (2) reveals that cross-strand aromatic interactions result in anomalous CD spectra in the region 200-240 nm for peptide 2. Similar anomalous electronic CD are observed in the three-stranded beta-sheet peptide Boc-Leu-Phe-Val-DPro-Gly-Leu-Val-Leu-Ala-DPro-Gly-Phe-Val-Leu-OMe (3), while the VCD spectrum is characteristic of beta-hairpin conformations. The identical VCD spectra obtained for the peptides 1 and 2 emphasize the utility of VCD, as compared to electronic CD, in the conformational analysis of peptides containing aromatic residues.\u