[Acceptor specificity of mannosyl transferases from Salmonella of serotypes C2 and C3]

Synthetic mono- and disaccharide derivatives of moraprenyl pyrophosphate were studied as mannose acceptors during the assembly of the repeating unit Rha-Man-Man-Gal of the Salmonella newport (serogroup C2) and S. kentucky (serogroup C3) O-antigens. Mannosyl transferases revealed strict specificity towards the configuration of terminal monosaccharide residue at C1 as well as to the type of linkage between monosaccharide residues in the disaccharide acceptor. The specificity of mannosyl transferases towards the structure of subterminal monosaccharide was not absolute. Alpha-D-Glucose and alpha-D-mannose derivatives were found not to serve as mannosyl residue acceptors, whereas those of alpha-D-talose, alpha-D-fucose, 4-deoxy-D-xylo-hexose and Man (alpha 1-3) glucose were substrates in enzymatic mannosylation with formation of polyprenyl pyrophosphate trisaccharides. These derivatives could serve as substrates for two subsequent enzymatic reactions: rhamnosylation and polymerization of the repeating units, yielding 40-60% of the polysaccharides.