Slow Dynamics of the Cyclic Osmoregulated Periplasmic Glucan of Ralstonia solanacearum As Revealed by Heteronuclear Relaxation Studies

Abstract

13C relaxation data obtained at different field strengths are reported for the osmoregulated periplasmic glucan (OPG) of Ralstonia solanacearum. Previous studies on this molecule showed that it is composed of 13 glucose units, linked all but one via β-(1−2) (Talaga et al. J. Bacteriol. 1996, 178, 2263−2271). The single α-(1−6) linkage induces structural constraints to such an extent that all individual anomeric proton resonances could be distinguished, opening the possibility of a genuine structure determination of this molecule. The relaxation data in this report agree well with the dynamical data extracted from the off-resonance ROESY experiments (Lippens et al. J. Am. Chem. Soc. 1996, 118, 7019−7027), but indicate as well an important exchange contribution to the T2 relaxation times. This latter event was shown to result from a large-scale motion on the microsecond time scale, especially affecting the residues downstream of the α-(1−6) linkage. Future atomic models of the compound will have to take into account the presence of conformational exchange.