Vacuum-ultraviolet circular dichroism analysis of biomolecules

Abstract

The vacuum-ultraviolet circular dichroism (VUVCD) spectra of various amino acids, saccharides, and proteins were measured using a synchrotron-radiation CD spectrophotometer at HiSOR/HSRC that is capable of measuring the CD spectra down to 140 nm in aqueous solution. L-Isomers of amino acids show two successive positive peaks at around 200 and 180 nm depending on the side chain. The ab initio assignment by time-dependent density functional theory predicts that these peaks are attributed to n-π* and π-π transitions of the carboxyl group, respectively. Most mono- and disaccharides exhibit characteristic peaks at around 170 nm, sensitively depending on the anomeric and axial/equatorial configurations of hydroxyl groups, trans-gauche conformations of the hydroxymethyl group, and the type of glycosidic linkage. The VUVCD spectra of 31 globular proteins allow us to estimate more accurately the content and number of α-helix and β-strand segments by extending the short-wavelength limit of the analytical program SELCON3 down to 160 nm. These results demonstrate that synchrotron-radiation VUVCD spectroscopy is a useful tool for structure analyses of biomolecules in solution based on the higher energy transitions of chromophores. © 2006 Wiley-Liss, Inc.