Vibrational Raman optical activity of lysozyme: hydrogen–deuterium exchange, unfolding and ligand binding
Measurements of the vibrational Raman optical activity (ROA) spectra of hen egg white lysozyme are reported which show that ROA is a useful new probe of protein secondary and tertiary structure and dynamics. ROA spectra can be measured just as easily in D2O as in H2O and a comparison of the two gives information about the relative exchange rates of the amide hydrogens in the peptide backbone for the various types of secondary and tertiary structure in lysozyme. Unfolded lysozyme shows a large conservative ROA couplet in the amide III region which might facilitate the identification of signatures in the ROA spectra of native proteins from irregular structures with the same type of conformational heterogeneity as that of an unfolded protein. The ROA spectrum of lysozyme bound to a saccharide inhibitor shows evidence for an increase in rigid loop content.