Enzymic Synthesis of Bacterial Polysaccharides from Modified Precursors

Enzymic Synthesis of Bacterial Polysaccharides from Modified Precursors 

Preparation of modified, bacterial polysaccharides having monosaccharide analogs inserted into the polymeric chain is of interest for study of the structure-properties relationship in these biopolymers. Incorporation of chemically prepared, modified, biosynthetic precursors of the polymers in enzymic reactions seems a promising approach for achieving this aim. Such an approach, which may be termed chemical-enzymic synthesis, has now been studied by our group,439-441 using O-specific polysaccharides (10-12) of Salmonella serogroups B and E as an example. 

To clarify the scope and the limitations of this approach, it was first of all necessary to ascertain whether precursors having modified monosaccharide residues may be accepted as substrates by the enzymes responsible both for assembly of the oligosaccharide repeating-units of the polymers and for their polymerization. 

Biosynthesis of repeating units of the main chain of these polysaccharides (see Section V,2,a) includes the consecutive transfer of a-D-galacto-pyranosyl phosphate from UDP-Gal, the L-rhamnopyranosyl group from dTDP-Rha, and the D-mannopyranosyl group from GDP-Man onto a poly- 

It may be seen that only several elements of the trisaccharide structure seem to be strictly controlled by the specificity of the enzymes. These include the anomeric configuration of the terminal monosaccharide residue of the glycosyl acceptor and the configuration of C-4 of the D-mannopyranosyl 

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VI. Enzymic Synthesis of Bacterial Polysaccharides from Modified Precursors... 

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