Structure of the O56 antigen of Escherichia coli, a polysaccharide containing 7-substituted alpha-N-acetylneuraminic acid

Characterization of two beta-1,3-glucosyltransferases from Escherichia coli serotypes O56 and O152

The O antigens of outer membrane-bound lipopolysaccharides (LPS) in gram-negative bacteria are oligosaccharides consisting of repeating units with various structures and antigenicities. The O56 and O152 antigens of Escherichia coli both contain a Glc-beta1-3-GlcNAc linkage within the repeating unit. We have cloned and identified the genes (wfaP in O56 and wfgD in O152) within the two O-antigen gene clusters that encode glucosyltransferases involved in the synthesis of this linkage. A synthetic substrate analog of the natural acceptor substrate undecaprenol-pyrophosphate-lipid [GlcNAc-alpha-PO3-PO3-(CH2)11-O-phenyl] was used as an acceptor and UDP-Glc as a donor substrate to demonstrate that both wfgD and wfaP encode glucosyltransferases. Enzyme products from both glucosyltransferases were isolated by high-pressure liquid chromatography and analyzed by nuclear magnetic resonance. The spectra showed the expected Glc-beta1-3-GlcNAc linkage in the products, confirming that both WfaP and WfgD are forms of UDP-Glc: GlcNAc-pyrophosphate-lipid beta-1,3-glucosyltransferases. Both WfaP and WfgD have a DxD sequence, which is proposed to interact with phosphate groups of the nucleotide donor through the coordination of a metal cation, and a short hydrophobic sequence at the C terminus that may help to associate the enzymes with the inner membrane. We showed that the enzymes have similar properties and substrate recognition. They both require a divalent cation (Mn2+ or Mg2+) for activity, are deactivated by detergents, have a broad pH optimum, and require the pyrophosphate-sugar linkage in the acceptor substrate for full activity. Substrates lacking phosphate or pyrophosphate linked to GlcNAc were inactive. The length of the aliphatic chain of acceptor substrates also contributes to the activity.

NMR reinvestigation of two N-acetylneuraminic acid-containing O-specific polysaccharides (O56 and O24) of Escherichia coli

Structures for the N-acetylneuraminic acid (Neu5Ac)-containing O56 and O24 polysaccharides of Escherichia coli have been reported previously. During these studies unusual chemical shifts had been observed for the NMR signals for H-3eq and C-3 of the Neu5Ac residues of both polysaccharides. In further pursuing this phenomenon, we have reinvestigated the O56 and O24 polysaccharides as well as derived oligosaccharides by one- and two-dimensional NMR spectroscopy. The results showed that structures of both polysaccharides (PSs) had to be modified and formulated as [formula: see text] 2D ROESY spectra revealed a strong NOE between H-3eq of Neu5Ac and the protons of the side-chain sugar (H-3 and H-5 of alpha-D-Gal p in the O56 PS and H-3 of alpha-D-Glc p in the O24 PS) and also between H-3ax of Neu5Ac and H-3 of beta-D-Glc p in the main chain. This indicated a close spatial association of the seven-linked alpha-Neu5Ac and the side-chain residues alpha-D-Gal p (O56 PS) and alpha-D-Glc p (O25 PS), respectively. The strong long-range spatial contacts caused the unusual chemical shifts of H-3eq and C-3 of Neu5Ac.

The structure of the O-specific polysaccharide from Escherichia coli O113 lipopolysaccharide

The O-specific polysaccharide from Escherichia coli O113 lipopolysaccharide was separated from the core and lipid A by mild acid hydrolysis and purified by GPC. Methylation analysis and 1H and 13C NMR spectroscopic studies of the O-deacetylated polysaccharide allowed the determination of the structure of the pentasaccharide repeating unit of the polysaccharide which can be written as [equation: see text] The position of the O-acetyl groups was not determined.

Structure of the Escherichia coli O24 and O56 O-specific sialic-acid-containing polysaccharides and linkage of these structures to the core region in lipopolysaccharides

The lipopolysaccharides from Escherichia coli O24 and O56 could be separated into higher-molecular-mass and lower-molecular-mass fractions. Mild acid hydrolysis of lipopolysaccharides of both serotypes released an O-specific polysaccharide and a tetrasaccharide repeating unit. Oligomers of the repeating unit, the core and the oligosaccharide that contains a fragment of the repeating unit linked to the core region were also obtained according to hydrolysis conditions. On the basis of sugar and methylation analyses, Smith degradation, fast-atom-bombardment mass spectrometry and NMR spectroscopy of the hydrolysis products, the biological repeating units of the O-specific polysaccharides were shown to be the following tetrasaccharides: [formula: see text] The structures differ from the structures proposed previously by Kogan et al. [Kogan, G., Shashkov, A. S., Jann, B. & Jann, K. (1993) Carbohydr. Res. 238, 261-270; Kogan, G., Jann, B. & Jann, K. (1993) Carbohydr. Res. 238, 335-338]. The O-specific repeating unit in E. coli O24 lipopolysaccharide is linked to O6 of the terminal D-galactose in the core region, whereas in O56 LPS the repeating unit is linked to O4 of a subterminal D-glucose residue in an R2 type core.

Structure of the O-specific polysaccharide of the O22-antigen (LPS) from Escherichia coli O22:K13

The polysaccharide moiety of the O22-antigen (lipopolysaccharide, LPS) consists of 2-acetamido-2-deoxy-D-galactose, D-glucuronic acid, D-glucose, and D-galactose in the molar ratios 2:1:1:1. Methylation analysis as well as 1D and 2D NMR spectroscopy showed that the O22 polysaccharide has the primary structure [formula: see text]