Scientific Publications by FDA Staff

Carbohydr Res 2005 Apr 11;340(5):863-74

The utility of residual dipolar couplings in detecting motion in carbohydrates: application to sucrose.

Venable RM, Delaglio F, Norris SE, Freedberg DI

Freedberg DI, US FDA, Ctr Biol Evaluat & Res, Biophys Lab, 1401 Rockville Pike, Rockville, MD 20852 USA US FDA, Ctr Biol Evaluat & Res, Biophys Lab, Rockville, MD 20852 USA NIDDK, Chem Phys Lab, NIH, Bethesda, MD 20892 USA

The solution structure and dynamics of sucrose are examined using a combination of NMR residual dipolar coupling and molecular mechanics force fields. It is found that the alignment tensors of the individual rings are different, and that fitting 35 measured residual dipolar couplings to structures with specific varphi, psi values indicates the presence of three major conformations: varphi, psi=(120 degrees ,270 degrees ), (45 degrees ,300 degrees ) and (90 degrees ,180 degrees ). Furthermore, fitting two structures simultaneously to the 35 residual dipolar couplings results in a substantial improvement in the fits. The existence of multiple conformations having similar stabilities is a strong indication of motion, due to the interconversion among these states. Results from four molecular mechanics force fields are in general agreement with the experimental results. However, there are major disagreements between force fields. Because fits of residual dipolar couplings to structures are dependent on the force field used to calculate the structures, multiple force fields were used to interpret NMR data. It is demonstrated that the pucker of the fructofuranosyl ring affects the calculated potential energy surface, and the fit to the residual dipolar couplings data. Previously published (13)C nuclear relaxation results suggesting that sucrose is rigid are not inconsistent with the present results when motional timescales are considered.