Department of Chemistry and Biochemistry, University of Maryland Baltimore County, Baltimore, MD 21228
While conformational models based on NOE data have been satisfactory for oligosaccharides which are relatively rigid, describing structures for flexible oligosaccharides is more difficult. We find that the simpler form of averaging 3J(CH) over multiple conformations makes it possible to construct a flexible model for the receptor polysaccharide of Streptococcus mitis J22 from long range heteronuclear coupling constants. Accurate coupling constants were derived from 3-d HMQC-NOESY data on a unformly C13 enriched polysaccharide without decoupling. Statistical weights of different conformers were extracted from linear fitting to the experimental data with 3J(CH) values calculated from a Karplus relation. The NOE data simulated from a statistically averaged complete relaxation matrix were also in agreement with experimental NOE data from a C13 decoupled 3-d HMQC-NOESY spectrum. The dynamic behavior of the the C13 labeled polysaccharide was studied by T1, T1rho and heteronuclear NOE measured with inverse detection. Selective excitation of the anomeric carbon atoms was used in order to simplify data analysis. The relaxation data were fit to various dynamics models of internal mobility for comparison with the structural models to provide insight into the role of polysaccharide dynamics in coaggregation of oral bacteria.