Recent Developments in Raman Optical Activity of Biopolymers

Abstract

Recent advances in Raman optical activity (ROA) instrumentation are outlined which have enhanced significantly the quality of vibrational ROA spectra of biopolymers in aqueous solution. Peptides, proteins, carbohydrates, glycoproteins, and nucleic acids now provide excellent ROA spectra which contain detailed information about solution structure. ROA spectra can be measured just as easily in D2O as in H2O solution, and, as illustrated for bovine serum albumin and concanavalin A, a comparison of the two can be highly informative. In addition to signatures of extended secondary structure, protein ROA spectra also contain signatures related to loops and turns which are valuable for studying tertiary structure and dynamics, exemplified here by a comparison of the ROA spectra of reduced lysozyme and unordered poly-L-lysine, by the ROA spectra of acid molten globule α-lactalbumin at different temperatures, which reveal a native-like tertiary fold, and by changes in the ROA spectrum of native lysozyme on binding to a saccharide inhibitor. Carbohydrate ROA spectra contain signatures of all the central features of their stereochemistry and, as shown by a comparison of laminaribiose with laminarin, can also probe extended secondary structure in polysaccharides. Results on a glycoprotein, orosomucoid, suggest that ROA can provide information about both the protein and the carbohydrate components. Preliminary results on nucleic acids are outlined with the ROA spectra of Poly(rA)·Poly(rU) and Poly(rI)·Poly(rC) shown as examples.