Structural characterization of a K-antigen capsular polysaccharide essential for normal symbiotic infection in Rhizobium sp. NGR234: Deletion of the rkpMNO locus prevents synthesis of 5,7-diacetamido-3,5,7,9-tetradeoxy-non-2-ulosonic acid

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Erscheinungsjahr:
2006
Medientyp:
Text
Schlagworte:
  • Antigens, Bacterial/chemistry
  • Antigens, Surface/chemistry
  • Bacterial Proteins/chemistry
  • Carbohydrate Sequence
  • Disaccharides/chemistry
  • Escherichia coli/metabolism
  • Gene Deletion
  • Models, Genetic
  • Molecular Sequence Data
  • Polysaccharides/chemistry
  • Rhizobium/metabolism
  • Sialic Acids/biosynthesis
Beschreibung:
  • Many early molecular events in symbiotic infection have been documented, although factors enabling Rhizobium to progress within the plant-derived infection thread and ultimately survive within the intracellular symbiosome compartment as mature nitrogen-fixing bacteroids are poorly understood. Rhizobial surface polysaccharides (SPS), including the capsular polysaccharides (K-antigens), exist in close proximity to plant-derived membranes throughout the infection process. SPSs are essential for bacterial survival, adaptation, and as potential determinants of nodulation and/or host specificity. Relatively few studies have examined the role of K-antigens in these events. However, we constructed a mutant that lacks genes essential for the production of the K-antigen strain-specific sugar precursor, pseudaminic acid, in the broad host range Rhizobium sp. NGR234. The complete structure of the K-antigen of strain NGR234 was established, and it consists of disaccharide repeating units of glucuronic and pseudaminic acid having the structure →4)-β-D- glucuronic acid-(1→4)-β-5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero- L-mannononulosonic acid-(2→. Deletion of three genes located in the rkp-3 gene cluster, rkpM, rkpN, and part of rkpO, abolished pseudaminic acid synthesis, yielding a mutant in which the strain-specific K-antigen was totally absent: other surface glycoconjugates, including the lipopolysaccharides, exopolysaccharides, and flagellin glycoprotein appeared unaffected. The NGRΔrkpMNO mutant was symbiotically defective, showing reduced nodulation efficiency on several legumes. K-antigen production was found to decline after rhizobia were exposed to plant flavonoids, and the decrease coincided with induction of a symbiotically active (bacteroid-specific) rhamnan-LPS, suggesting an exchange of SPS occurs during bacterial differentiation in the developing nodule. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.
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  • info:eu-repo/semantics/openAccess
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Forschungsinformationssystem der UHH
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oai:www.edit.fis.uni-hamburg.de:publications/861c99a5-0544-4fc3-9046-8425eebbcbe3