title: The capsular polysaccharide of Bacteroides fragilis comprises two ionically linked polysaccharides.
abstract: 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.
authors.affiliation: Channing Laboratory, Brigham and Women's Hospital, Boston, Massachusetts 02115.
authors.forename: A O
authors.initials: AO
authors.lastname: Tzianabos
authors.forename: A
authors.initials: A
authors.lastname: Pantosti
authors.forename: H
authors.initials: H
authors.lastname: Baumann
authors.forename: J R
authors.initials: JR
authors.lastname: Brisson
authors.forename: H J
authors.initials: HJ
authors.lastname: Jennings
authors.forename: D L
authors.initials: DL
authors.lastname: Kasper
mesh_terms: D001441:Bacteroides fragilis / Q000378:metabolism* / Q000648:ultrastructure; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D007122:Immunoelectrophoresis; D007525:Isoelectric Focusing; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D011135:Polysaccharides, Bacterial