Our goal is to develop vacuum ultraviolet circular dichroism (VUCD) as a structural tool for conformational studies of biopolymers in general, and carbohydrates (polysaccharides) in particular. The general approach has been to combine experimental and theoretical methods where applicable. During the next three years VUCD spectra of selected polysaccharides will be obtained, which will allow a delineation of the contributions of the various factors which determine VUCD spectra; e.g., interresidue rotational angles, anomeric configuration, linkage type, protonation, substituent groups, and hydrogen bonding. Polysaccharides to be studied include xylan, carrageenan, xanthan, galactan, polymannuronate and polyguluronate. VUCD measurements will also be extended to include glycoproteins. Fibronectin plays a role in cell adhesion, cell migration and embryonic differentiation. It exhibits affinities for heparin and other macromolecules, and the interactions are known to have their origin in discrete domains of the fibronectin molecule. Fibronectin has little, if any, helical structure. We will use VUCD spectroscopy to probe the native conformation, and the conformational changes that occur upon heparin binding. Model theoretical calculations will be carried out to determine the origin of a recently discovered sector rule which successfully accounts for the sign of the VUCD in all polysaccharide systems studied to date. Exciton contributions and the role of Sigma-Sigma* transitions to polysaccharide VUCD will be evaluated. The objective of these calculations is to develop a theoretical basis for interpreting polysaccharide VUCD.
