Vibrational circular dichroism of β-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 similar to 1643-1659 cm(-1) region, and a weak positive VCD band at similar to 1693 cm(-1). These spectral features are diagnostic of beta-hairpins cm 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-(D)Pro-Gly-LeuPhe-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-(D)Pro-Gly-Leu-Val-Leu-Ala-(D)Pro-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.