SLOW DYNAMICS OF THE CYCLIC OSMOREGULATED PERIPLASMIC GLUCAN OF RALSTONIA-SOLANACEARUM AS REVEALED BY HETERONUCLEAR RELAXATION STUDIES

C-13 relaxation data obtained at different field strengths are reporte d for the osmoregulated periplasmic glucan (OPG) of Ralstonia solanace arum. Previous studies on this molecule showed that it is composed of 13 glucose units, linked all but one via beta-(1-2) (Talaga et al. J. Bacteriol. 1996, 178, 2263-2271). The single alpha-(1-6) linkage induc es structural constraints to such an extent that all individual anomer ic proton resonances could be distinguished, opening the possibility o f a genuine structure determination of this molecule. The relaxation d ata in this report agree well with the dynamical data extracted from t he off-resonance ROESY experiments (Lippens et al. J. Am. Chem. Sec. 1 996, 118, 7019-7027), but indicate as well an important exchange contr ibution to the T-2 relaxation times. This latter event was shown to re sult from a large-scale motion on the microsecond time scale, especial ly affecting the residues downstream of the alpha-(1-6) linkage. Futur e atomic models of the compound will have to take into account the pre sence of conformational exchange.