Structural studies of the Escherichia coli O90 O-antigen polysaccharide

A bifunctional Pasteurella multocida β1-3-galactosyl/N-acetylgalactosaminyltransferase (PmNatB) for the highly efficient chemoenzymatic synthesis of disaccharides

Glycosyltransferases are nature's key biocatalysts for the formation of glycosidic bonds. Discovery and characterization of new synthetically useful glycosyltransferases are critical for the development of efficient enzymatic and chemoenzymatic strategies for producing complex carbohydrates and glycoconjugates. Herein we report the identification of Pasteurella multocida PmNatB as a bifunctional single-catalytic-domain glycosyltransferase with both β1-3-galactosyltransferase and β1-3-N-acetylgalactosaminyltransferase activities. It is a novel glycosyltransferase for constructing structurally diverse GalNAcβ3Galα/βOR and Galβ3GalNAcα/βOR disaccharides in one-pot multienzyme systems with in situ generation of UDP-sugars.

Structure and genetics of Escherichia coli O antigens

Escherichia coli includes clonal groups of both commensal and pathogenic strains, with some of the latter causing serious infectious diseases. O antigen variation is current standard in defining strains for taxonomy and epidemiology, providing the basis for many serotyping schemes for Gram-negative bacteria. This review covers the diversity in E. coli O antigen structures and gene clusters, and the genetic basis for the structural diversity. Of the 187 formally defined O antigens, six (O31, O47, O67, O72, O94 and O122) have since been removed and three (O34, O89 and O144) strains do not produce any O antigen. Therefore, structures are presented for 176 of the 181 E. coli O antigens, some of which include subgroups. Most (93%) of these O antigens are synthesized via the Wzx/Wzy pathway, 11 via the ABC transporter pathway, with O20, O57 and O60 still uncharacterized due to failure to find their O antigen gene clusters. Biosynthetic pathways are given for 38 of the 49 sugars found in E. coli O antigens, and several pairs or groups of the E. coli antigens that have related structures show close relationships of the O antigen gene clusters within clades, thereby highlighting the genetic basis of the evolution of diversity.

The structures ofEscherichia coliO-polysaccharide antigens

Escherichia coli is usually a non-pathogenic member of the human colonic flora. However, certain strains have acquired virulence factors and may cause a variety of infections in humans and in animals. There are three clinical syndromes caused by E. coli: (i) sepsis/meningitis; (ii) urinary tract infection and (iii) diarrhoea. Furthermore the E. coli causing diarrhoea is divided into different 'pathotypes' depending on the type of disease, i.e. (i) enterotoxigenic; (ii) enteropathogenic; (iii) enteroinvasive; (iv) enterohaemorrhagic; (v) enteroaggregative and (vi) diffusely adherent. The serotyping of E. coli based on the somatic (O), flagellar (H) and capsular polysaccharide antigens (K) is used in epidemiology. The different antigens may be unique for a particular serogroup or antigenic determinants may be shared, resulting in cross-reactions with other serogroups of E. coli or even with other members of the family Enterobacteriacea. To establish the uniqueness of a particular serogroup or to identify the presence of common epitopes, a database of the structures of O-antigenic polysaccharides has been created. The E. coli database (ECODAB) contains structures, nuclear magnetic resonance chemical shifts and to some extent cross-reactivity relationships. All fields are searchable. A ranking is produced based on similarity, which facilitates rapid identification of strains that are difficult to serotype (if known) based on classical agglutinating methods. In addition, results pertinent to the biosynthesis of the repeating units of O-antigens are discussed. The ECODAB is accessible to the scientific community at http://www.casper.organ.su.se/ECODAB/.

Two different O-polysaccharides from Escherichia coli O86 are produced by different polymerization of the same O-repeating unit

The structure of a new O-polysaccharide from Escherichia coli O86:K62:B7 was determined using NMR and methylation analysis. The structure is as follows: [carbohydrate: see text]. Comparison with the previously published structure from E. coli O86:K2:H2 revealed that the O-polysaccharides from these two E. coli O86 serotypes share the same branched pentasaccharide repeating unit. However, they differ in the anomeric configuration of the linkage, the linkage position, and the identity of the residue through which polymerization occurs. The immunochemical activity of these two forms of LPS toward anti-B antibody was studied and compared. The results showed that LPS from E. coli O86:K2:H2 strain possesses higher blood group B reactivity. The immunoreactivity difference was explained by modeling of the O-repeating unit tetrasaccharide fragments. This finding provides a good system for the further study of O-polysaccharide biosynthesis especially the repeating unit polymerization mechanism.

Controlled study of cytolethal distending toxin-producing Escherichia coli infections in Bangladeshi children

The role of cytolethal distending toxin (CDT)-producing Escherichia coli, a newly described category of E. coli, in the causation of diarrhea was studied by screening E. coli isolates from 546 children < 5 years of age with diarrhea and 215 matched controls without diarrhea by using a specific DNA probe. Although CDT-positive E. coli strains were isolated from more children with diarrhea than from healthy controls (3.1 versus 0.93%), this difference did not reach statistical significance (P = 0.082). All CDT-positive strains also possessed the virulence factors of enteropathogenic E. coli or enteroaggregative E. coli isolates.