Synthesis of GDP-Mannose and Mannosylglycerate from Labeled Mannose by Genetically Engineered Escherichia coli without Loss of Specific Isotopic Enrichment

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American Society for Microbiology

RESUMO

We report the construction of an Escherichia coli mutant that harbors two compatible plasmids and that is able to synthesize labeled 2-O-α-d-mannosyl-d-glycerate from externally added labeled mannose without the loss of specific isotopic enrichment. The strain carries a deletion in the manA gene, encoding phosphomannose isomerase. This deletion prevents the formation of fructose-6-phosphate from mannose-6-phosphate after the uptake of mannose from the medium by mannose-specific enzyme II of the phosphotransferase system (PtsM). The strain also has a deletion of the cps gene cluster that prevents the synthesis of colanic acid, a mannose-containing polymer. Plasmid-encoded phosphomannomutase (cpsG) and mannose-1-phosphate guanylyltransferase (cpsB) ensure the formation of GDP-mannose. A second plasmid harbors msg, a gene from Rhodothermus marinus that encodes mannosylglycerate synthase, which catalyzes the formation of 2-O-α-d-mannosyl-d-glycerate from GDP-mannose and endogenous glycerate. The rate-limiting step in 2-O-α-d-mannosyl-d-glycerate formation is the transfer of GDP-mannose to glycerate. 2-O-α-d-mannosyl-d-glycerate can be released from cells by treatment with cold-water shock. The final product is formed in a yield exceeding 50% the initial quantity of labeled mannose, including loss during preparation and paper chromatography.

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