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

• Published in: Glycobiology (Oxford) 2005-01, Vol.15 (1), p.101-108
• Main Authors: Fraysse, N., Lindner, B., Kaczynski, Z., Sharypova, L., Holst, O., Niehaus, K., Poinsot, V.
• Format: Article
• Language: English
• Subjects: Biopolymers - chemistry; Biopolymers - metabolism; capillary skimmer dissociation; capsular polysaccharide; capsular polysaccharides; Chromatography, Thin Layer; correlation spectroscopy; COSY; CPS; CSD; deoxycholic acid; DOC; electrospray ionization; EPS; ESI; exopolysaccharide; Fourier transform ion cyclotron resonance; FT-ICR; high molecular mass; HMM; K-antigen capsular polysaccharide; KPS; lipopolysaccharide; LMM; low molecular mass; LPS; Magnetic Resonance Spectroscopy; MALDI-TOF; mass spectrometry; matrix-assisted laser desorption ionization time of flight; Molecular Weight; MS/MS; NMR; nuclear magnetic resonance; PAGE; phospholipic anchor; Phospholipids - chemistry; Phospholipids - metabolism; polyacrylamide gel electrophoresis; Polysaccharides - chemistry; Polysaccharides - metabolism; QTOF; QTOF MS; quadrupole time-of-flight; Sinorhizobium meliloti; Sinorhizobium meliloti - classification; Sinorhizobium meliloti - metabolism; Spectrometry, Mass, Electrospray Ionization; Sugar Acids - metabolism; tandem mass spectrometry; thin-layer chromatography; TLC; tryptone-yeast extract
• ISSN: 0959-6658; 1460-2423; 1460-2423
• DOI: 10.1093/glycob/cwh142

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 β-(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.