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Journal of Bacteriology, July 2005, p. 4470-4479, Vol. 187, No. 13
0021-9193/05/$08.00+0     doi:10.1128/JB.187.13.4470-4479.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Initiation and Synthesis of the Streptococcus pneumoniae Type 3 Capsule on a Phosphatidylglycerol Membrane Anchor

Robert T. Cartee, W. Thomas Forsee, and Janet Yother*

Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294

Received 28 February 2005/ Accepted 30 March 2005

The type 3 synthase from Streptococcus pneumoniae is a processive ß-glycosyltransferase that assembles the type 3 polysaccharide [3)-ß-D-GlcUA-(1->4)-ß-D-Glc-(1->] by a multicatalytic process. Polymer synthesis occurs via alternate additions of Glc and GlcUA onto the nonreducing end of the growing polysaccharide chain. In the presence of a single nucleotide sugar substrate, the type 3 synthase ejects its nascent polymer and also adds a single sugar onto a lipid acceptor. Following single sugar incorporation from either UDP-[14C]Glc or UDP-[14C]GlcUA, we found that phospholipase D digestion of the Glc-labeled lipid yielded a product larger than a monosaccharide, while digestion of the GlcUA-labeled lipid resulted in a product larger than a disaccharide. These data indicated that the lipid acceptor contained a headgroup and that the order of addition to the lipid acceptor was Glc followed by GlcUA. Higher-molecular-weight product synthesized in vitro was also sensitive to phospholipase D digestion, suggesting that the same lipid acceptor was being used for single sugar additions and for polymer formation. Mass spectral analysis of the anionic lipids of a type 3 S. pneumoniae strain demonstrated the presence of glycosylated phosphatidylglycerol. This lipid was also observed in Escherichia coli strains expressing the recombinant type 3 synthase. The presence of the lipid primer in S. pneumoniae membranes explained both the ability of the synthase to reinitiate polysaccharide synthesis following ejection of its nascent chain and the association of newly synthesized polymer with the membrane. Unlike most S. pneumoniae capsular polysaccharides, the type 3 capsule is not covalently linked to the cell wall. The present data indicate that phosphatidylglycerol may anchor the type 3 polysaccharide to the cell membrane.

* Corresponding author. Mailing address: Department of Microbiology, BBRB 661/12, 845 19th St. South, Birmingham, AL 35294. Phone: (205) 934-9531. Fax: (205) 975-6715. E-mail: jyother{at}uab.edu.

Journal of Bacteriology, July 2005, p. 4470-4479, Vol. 187, No. 13
0021-9193/05/$08.00+0     doi:10.1128/JB.187.13.4470-4479.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Forsee, W. T., Cartee, R. T., Yother, J. (2009). A Kinetic Model for Chain Length Modulation of Streptococcus pneumoniae Cellubiuronan Capsular Polysaccharide by Nucleotide Sugar Donor Concentrations. J. Biol. Chem. 284: 11836-11844 [Abstract] [Full Text]  
  • Forsee, W. T., Cartee, R. T., Yother, J. (2009). Characterization of the Lipid Linkage Region and Chain Length of the Cellubiuronic Acid Capsule of Streptococcus pneumoniae. J. Biol. Chem. 284: 11826-11835 [Abstract] [Full Text]  
  • Aanensen, D. M., Mavroidi, A., Bentley, S. D., Reeves, P. R., Spratt, B. G. (2007). Predicted Functions and Linkage Specificities of the Products of the Streptococcus pneumoniae Capsular Biosynthetic Loci. J. Bacteriol. 189: 7856-7876 [Abstract] [Full Text]  
  • Forsee, W. T., Cartee, R. T., Yother, J. (2006). Role of the Carbohydrate Binding Site of the Streptococcus pneumoniae Capsular Polysaccharide Type 3 Synthase in the Transition from Oligosaccharide to Polysaccharide Synthesis. J. Biol. Chem. 281: 6283-6289 [Abstract] [Full Text]  


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