Solution conformation and dynamics of a tetrasaccharide related to the Lewis(x) antigen deduced by NMR relaxation measurements.

Abstract

1H-NMR cross-relaxation rates and nonselective longitudinal relaxation times have been obtained at two magnetic fields (7.0 and 11.8 T) and at a variety of temperatures for the branched tetrasaccharide methyl 3-O-alpha-N-acetyl-galactosaminyl-beta-galactopyranosyl-(1-->4)[3-O-alph a -fucosyl]-glucopyranoside (1), an inhibitor of astrocyte growth. In addition, 13C-NMR relaxation data have also been recorded at both fields. The 1H-NMR relaxation data have been interpreted using different motional models to obtain proton-proton correlation times. The results indicate that the GalNAc and Fuc rings display more extensive local motion than the two inner Glc and Gal moieties, since those present significantly shorter local correlation times. The 13C-NMR relaxation parameters have been interpreted in terms of the Lipari-Szabo model-free approach. Thus, order parameters and internal motion correlation times have been deduced. As obtained for the 1H-NMR relaxation data, the two outer residues possess smaller order parameters than the two inner rings. Internal correlation times are in the order of 100 ps. The hydroxymethyl groups have also different behaviour, with the exocyclic carbon on the glucopyranoside unit showing the highest S2. Molecular dynamics simulations using a solvated system have also been performed and internal motion correlation functions have been deduced from these calculations. Order parameters and interproton distances have been compared to those inferred from the NMR measurements. The obtained results are in fair agreement with the experimental data.