VCD spectroscopic properties of the β-hairpin forming miniprotein CLN025 in various solvents

Electronic and vibrational circular dichroism are often used to determine the secondary structure of proteins, because each secondary structure has a unique spectrum. Little is known about the vibrational circular dichroic spectroscopic features of the β-hairpin. In this study, the VCD spectral features of a decapeptide, YYDPETGTWY (CLN025), which forms a stable β-hairpin that is stabilized by intramolecular weakly polar interactions and hydrogen bonds were determined. Molecular dynamics simulations and ECD spectropolarimetry were used to confirm that CLN025 adopts a β-hairpin in water, TFE, MeOH, and DMSO and to examine differences in the secondary structure, hydrogen bonds, and weakly polar interactions. CLN025 was synthesized by microwave-assisted solid phase peptide synthesis with N^α-Fmoc protected amino acids. The VCD spectra displayed a (-,+,-) pattern with bands at 1640 to 1656 cm^-1, 1667 to 1687 cm^-1, and 1679 to 1686 cm^-1 formed by the overlap of a lower frequency negative couplet and a higher frequency positive couplet. A maximum IR absorbance was observed at 1647 to 1663 cm^-1 with component bands at 1630 cm^-1, 1646 cm^-1, 1658 cm^-1, and 1675 to 1680 cm^-1 that are indicative of the β-sheet, random meander, either random meander or loop and turn, respectively. These results are similar to the results of others, who examined the VCD spectra of β-hairpins formed by ^DPro-Xxx turns and indicated that observed pattern is typical of β-hairpins.