| Sujet | acids; antibodies; antibody; bacterial; Bacteroides fragilis; biochemistry; biosynthesis; capsular polysaccharide; capsule; carbohydrate conformation; carbohydrate sequence; cells; cell surface; chemistry; complexes; electron; forms; high-resolution; immunoelectrophoresis; interaction; isoelectric focusing; isolation & purification; laboratories; magnetic resonance spectroscopy; metabolism; methods; microscopy; microscopy, immunoelectron; molecular; molecular sequence data; molecular structure; molecular weight; monoclonal-antibodies; monoclonal-antibody; NMR spectroscopy; polysaccharides; polysaccharides, bacterial; repeating unit; resolution; resolution NMR spectroscopy; spectroscopy; structural; structure; substituent; support, non-U.S. Gov't; support, U.S. Gov't, P.H.S.; surface; ultrastructure; unit |
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| Résumé | Recently, we have shown that the capsular polysaccharide of Bacteroides fragilis NCTC 9343 is composed of an aggregate of two discrete large molecular weight polysaccharides (designated polysaccharides A and B). Following disaggregation of this capsular complex by very mild acid treatment, high resolution NMR spectroscopy demonstrated that polysaccharides A and B consist of highly charged repeating unit structures with unusual substituent groups (Baumann, H., Tzianabos, A. O., Brisson, J.-R., Kasper, D.L., and Jennings, H.J. (1992) Biochemistry 31, 4081-4089). Presently, we report that the capsular polysaccharide of B. fragilis represents a complex structure that is formed as a result of ionic interactions between polysaccharides A and B. Electron microscopy of immunogold-labeled organisms (with monoclonal antibodies specific for polysaccharides A and B) demonstrated that the two polysaccharides are co-expressed on the cell surface of B. fragilis. We have shown that the purified capsule complex is made up exclusively of polysaccharide A and polysaccharide B (no other macromolecular structure was detected) in a 1:3.3 ratio and that disaggregation of this complex into the native forms of the constituent polysaccharides could be accomplished by preparative isoelectric focusing. Structural analyses of the native polysaccharides A and B showed that they possessed the same repeating unit structures as the respective acid-derived polysaccharides. The ionic nature of the linkage between polysaccharides A and B was demonstrated by reassociation of the native polysaccharides to form an aggregated polymer comparable to the original complex. The distinctive composition of this macromolecule may provide a rationale for the unusual biologic properties associated with the B. fragilis capsular polysaccharide |
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