Metropolis Monte Carlo simulations have been performed on four substructures from the call-wall polysaccharide antigen of Streptococcus group A to explore the conformational begaviour of these compounds. The compounds examined are the trisaccharide, propyl 3-O-(2-acetamido-2-deoxy-b-D-glucopyranosyl)-2-O-(a-L-rhamnopyranosyl)-a-L-rhamnopyranoside, 1, the tetrasaccharide, propyl 3-O-(3-O-(2-acetamido-2-deoxy-b-D-glucopyranosyl)-2-O-(a-L-rhamnopyranosyl)-a-L-rhamnopyranosyl)-a-L-rhamnopyranoside, 2, the hexasacchride, propyl 3-O-(2-O-(3-O-(3-O-(2-acetamido-2-deoxy-bDglucopyranosyl)-a-L-rhamnopyranosyl)-a-L-rhamnopyranosyl)-3-O-(2-acetamido-2-deoxy-b-D-glucopyranosyl)-a-L-rhamnopyranosyl)-a-L-rhamnopyranoside, 3, and the hexasaccharide, propyl 3-O-(2-acetamido-2-deoxy-b-D-glucopyranosyl)-2-O-(3-O-(3-O-(2-acetamido-2-deoxy-b-D-glucopyranosyl)-2-O-(a-L-rhamnopyranosyl)-a-L-rhamnopyranosyl)-a-L-rhamnopyranosyl)-a-L-rhamnopyranoside, 4. In general, the conformational flexibility of simular glycosidic linkages in different compounds is comparable. However, in a few cases, small differences in the conformations available to these linkages in different structural environments could be detected. Interestingly, a secon conformation found for the b-D-GlcNAc-(1→3)-a-L-Rha linkage in three of the compounds was not populated in the hexasaccharide 4. Futhermore, a conformational locale of the a-L-Rha-(1→3)-a-L-Rha linkage found to by populated in the trisaccaharide 1, tetrasaccahride 2, and hexasaccharide 4 is negligibly populated in the hexasaccharide 3. Ensemble averaged proton-proton disances compare favourably with experimental average distances obtained fro mNMR spectroscopy. The trisaccharide branch point in the hexasaccharides is shown to by a hoghly defined conformational feature. The same unit has been found to by one of the crucial elements recognized by anti-Group A Streptococcus antibodies, a result that has implications for the design of improved immunodiagnostics and vaccines.
Oligosaccharides, Metropolis Monte Carlo simulations, Cell-wall polysaccharide, Streptococcus group A
NCBI PubMed ID: 8593633Journal NLM ID: 0043535Publisher: Elsevier
Institutions: Department of Chemistry, Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Valby, Copenhagen, Denmark, Department of Chemistry, Simon Fraser University, Burnaby, B.C. V5A 1S6, Canada
Methods: NMR, conformation analysis
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