The NMR group in the Laboratory of Biophysics focuses on understanding the structure and dynamics of carbohydrates and proteins. We determined and compared the structure and dynamics of alpha- and beta-lactose using residual dipolar couplings, which were measured using new solution NMR techniques developed in our group. Although the two anomers of lactose differ only by their configuration at the anomeric (a stereochemical difference), their three-dimensional structures are significantly different. This structural difference may be the basis for enzymatic recognition of one anomer over another. A more subtle point found in our studies is the detection of dynamics about the glycosidic bond. This type of motion had long been suspected in carbohydrates. Though alpha- and beta-lactose appear to be rigid from 13C relaxation data, residual dipolar couplings detected this type of motion. Thus, upon comparison, even the motion in alpha-lactose differs from that in beta-lactose. We are also focusing on a detailed understanding of the methods we use to measure long-range residual dipolar couplings. We have found that even at very high magnetic fields, strong coupling reduces the accuracy of the measured couplings, and are currently exploring solutions to this problem. We are also investigating the structure of cellobiose using residual dipolar couplings to develop a basis for future projects involving polysaccharide vaccine characterization. As part of our studies on biomolecules, we are investigating the structure and dynamics of a polypeptide (38 amino acids) from HIV gp41.
