Glycobiology Advance Access originally published online on September 8, 2004
Glycobiology 2005 15(1):101-108; doi:10.1093/glycob/cwh142
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Glycobiology vol. 15 no. 1 © Oxford University Press 2005; all rights reserved.
Sinorhizobium meliloti strain 1021 produces a low-molecular-mass capsular polysaccharide that is a homopolymer of 3-deoxy-D-manno-oct-2-ulosonic acid harboring a phospholipid anchor
2 Department of Genetics, Faculty of Biology, University of Bielefeld, D-33615 Bielefeld, Germany; 3 Division of Biophysics, Research Center Borstel, Leibniz Center for Medicine and Biosciences, D-23845 Borstel, Germany; 4 Division of Structural Biochemistry, Research Center Borstel, Leibniz Center for Medicine and Biosciences, D-23845 Borstel, Germany; and 5 Laboratoire des IMRCP, Universite Paul Sabatier, F-31062 Toulouse, France
1 To whom correspondence should be addressed; e-mail: nfraysse{at}genetik.uni-bielefeld.de
Received on July 20, 2004; revised on August 19, 2004; accepted on August 23, 2004
Sinorhizobium meliloti strain 1021 possesses the particularity to synthesize biologically inefficient capsular polysaccharides (KPS). It has been assumed that this class of compounds is not produced in high-molecular-mass (HMM) forms, even if many genetic analyses show the existence of expression of genes involved in the biosynthesis of capsular polysaccharides. The expression of these genes that are involved in the export of a KPS throughout the membrane and in the attachment of a lipid moiety has never been related to a structurally characterized surface polysaccharide. It is now reported that S. meliloti strain 1021 produces low-molecular-mass polysaccharides (4–4.5 kDa) that are exclusively composed of ß-(2
7)-linked 3-deoxy-D-manno-oct-2-ulopyranosonic acid (Kdo) residues. These compounds are considered precursor molecules of HMM KPS, whose biosynthesis is arrested in the case of S. meliloti strain 1021. For the first time, the phospholipid anchor of a rhizobial KPS has been found, and its structure could be partially identified—namely, a phosphoglycerol moiety bearing a hydroxy-octacosanoic acid. When compared to other rhizobial KPS (composed of dimeric hexose-Kdo-like sugar repeating units), the Kdo homopolymer described here may explain why a complementation of S. meliloti strain 1021 Exo B mutant with an effective rkpZ gene restoring an active higher KPS size does not completely lead to the fully effective nitrogen fixing phenotype.
Key words: capsular polysaccharides / Fourier transform ion cyclotron resonance / phospholipic anchor / QTOF MS / Sinorhizobium meliloti
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