Vibrational Raman optical activity of biopolymers
Advances in Raman optical activity (ROA) instrumentation have enhanced the sensitivity to the level necessary to provide vibrational ROA spectra of biological molecules in aqueous solution. Biopolymers such as peptides, proteins, carbohydrates and glycoproteins often provide good ROA spectra which contain detailed information about solution structure and conformation. ROA spectra can be measured just as easily in D2O as in H2O solution and, as illustrated for bovine serum albumin, a comparison of the two can be highly informative. In addition to clear signatures of extended secondary structures, such as α-helix and β-sheet, protein ROA spectra also contain signatures, possibly related to loops and turns, which should be valuable for studying the tertiary structure and dynamics of proteins, exemplified here by a comparison of the ROA spectra of unfolded and native lysozyme, lysozyme bound to a saccharide inhibitor and α-lactalbumin. Carbohydrate ROA spectra contain signatures of all the central features of carbohydrate stereochemistry and, as shown by a comparison of the disaccharide laminaribiose with laminarin, can also probe extended secondary structure in polysaccharides. Finally, a study of a glycoprotein, orosomucoid, shows that ROA can provide information about both the protein and the carbohydrate components and the mutual influence they exert on each other's stability and conformation.