부산대학교 도서관

The structure of the O-antigen from the international reference strain Escherichia coli O93:−:H16 has been determined. A nonrandom modal chain-length distribution was observed for the lipopolysaccharide, a pattern which is typical when long O-specific polysaccharides are expressed. By a combination of (i) bioinformatics information on the gene cluster related to O-antigen synthesis including putative function on glycosyl transferases, (ii) the magnitude of NMR coupling constants of anomeric protons, and (iii) unassigned 2D 1H, 13C-HSQC, and 1H,1H-TOCSY NMR spectra it was possible to efficiently elucidate the structure of the carbohydrate polymer in an automated fashion using the computer program CASPER. The polysaccharide also carries O -acetyl groups and their locations were determined by 2D NMR experiments showing that ~½ of the population was 2,6-di- O -acetylated, ~¼ was 2- O -acetylated, whereas ~¼ did not carry O -acetyl group(s) in the 3- O -substituted mannosyl residue of the repeating unit. The structure of the tetrasaccharide repeating unit of the O-antigen is given by: →2)-β- d -Man p -(1→3)-β- d -Man p 2Ac6Ac-(1→4)-β- d -Glc p A-(1→3)-α- d -Glc p NAc-(1→, which should also be the biological repeating unit and it shares structural elements with capsular polysaccharides from E. coli K84 and K50. The structure of the acidic O-specific polysaccharide from Cellulophaga baltica strain NN015840T differs to that of the O-antigen from E. coli O93 by lacking the O -acetyl group at O6 of the O -acetylated mannosyl residue. [ABSTRACT FROM AUTHOR]