Mechanism of type 3 capsular polysaccharide synthesis in Streptococcus pneumoniae

Academic Article


  • The glycosidic linkages of the type 3 capsular polysaccharide of Streptococcus pneumoniae ([3)-β-D-GlcUA-(1→4)-β-D-Glc-(1→](n)) are formed by the membrane-associated type 3 synthase (Cps3S), which is capable of synthesizing polymer from UDP sugar precursors. Using membrane preparations of S. pneumoniae in an in vitro assay, we observed type 3 synthase activity in the presence of either Mn2+ or Mg2+ with maximal levels seen with 10- 20 nM Mn2+. High molecular weight polymer synthesized in the assay was composed of Glc and glucuronic acid and could be degraded to a low molecular weight product by a type 3-specific depolymerase from Bacillus circulans. Additionally, the polymer bound specifically to an affinity column made with a type 3 polysaccharide-specific monoclonal antibody. The polysaccharide was rapidly synthesized from smaller chains and remained associated with the enzyme-containing membrane fraction throughout its synthesis, indicating a processive mechanism of synthesis. Release of the polysaccharide was observed, however, when the level of one of the substrates became limiting. Finally, addition of sugars to the growing type 3 polysaccharide was shown to occur at the nonreducing end of the polysaccharide chain.
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    Digital Object Identifier (doi)

    Author List

  • Cartee RT; Forsee WT; Schutzbach JS; Yother J
  • Start Page

  • 3907
  • End Page

  • 3914
  • Volume

  • 275
  • Issue

  • 6