In Vitro Biosynthesis and Chemical Identification of UDP-N-acetyl-d-quinovosamine (UDP-d-QuiNAc)

• Published in: The Journal of biological chemistry Vol. 289; no. 26; pp. 18110 - 18120
• Main Authors: Li, Tiezheng, Simonds, Laurie, Kovrigin, Evgenii L., Noel, K. Dale
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 27.06.2014; American Society for Biochemistry and Molecular Biology
• Subjects: Acetylglucosamine - chemistry; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Biocatalysis; Carbohydrate Biosynthesis; Glycobiology; Glycobiology and Extracellular Matrices; Nuclear Magnetic Resonance (NMR); Oxidoreductases - chemistry; Oxidoreductases - genetics; Oxidoreductases - isolation & purification; Oxidoreductases - metabolism; Reductase; Rhizobium etli; Rhizobium etli - enzymology; Rhizobium etli - genetics; UDP-2-acetamido-2,6-dideoxy-d-xylo-4-hexulose; UDP-d-GlcNAc; UDP-d-QuiNAc; WreQ; Glycobiology; UDP-2-acetamido-2,6-dideoxy-d-xylo-4-hexulose; Rhizobium etli; Bacteria; UDP-d-GlcNAc; Carbohydrate Biosynthesis; UDP-d-QuiNAc; WreQ; Nuclear Magnetic Resonance (NMR); Reductase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.555862

N-acetyl-d-quinovosamine (2-acetamido-2,6-dideoxy-d-glucose, QuiNAc) occurs in the polysaccharide structures of many Gram-negative bacteria. In the biosynthesis of QuiNAc-containing polysaccharides, UDP-QuiNAc is the hypothetical donor of the QuiNAc residue. Biosynthesis of UDP-QuiNAc has been proposed to occur by 4,6-dehydration of UDP-N-acetyl-d-glucosamine (UDP-GlcNAc) to UDP-2-acetamido-2,6-dideoxy-d-xylo-4-hexulose followed by reduction of this 4-keto intermediate to UDP-QuiNAc. Several specific dehydratases are known to catalyze the first proposed step. A specific reductase for the last step has not been demonstrated in vitro, but previous mutant analysis suggested that Rhizobium etli gene wreQ might encode this reductase. Therefore, this gene was cloned and expressed in Escherichia coli, and the resulting His6-tagged WreQ protein was purified. It was tested for 4-reductase activity by adding it and NAD(P)H to reaction mixtures in which 4,6-dehydratase WbpM had acted on the precursor substrate UDP-GlcNAc. Thin layer chromatography of the nucleotide sugars in the mixture at various stages of the reaction showed that WbpM converted UDP-GlcNAc completely to what was shown to be its 4-keto-6-deoxy derivative by NMR and that addition of WreQ and NADH led to formation of a third compound. Combined gas chromatography-mass spectrometry analysis of acid hydrolysates of the final reaction mixture showed that a quinovosamine moiety had been synthesized after WreQ addition. The two-step reaction progress also was monitored in real time by NMR. The final UDP-sugar product after WreQ addition was purified and determined to be UDP-d-QuiNAc by one-dimensional and two-dimensional NMR experiments. These results confirmed that WreQ has UDP-2-acetamido-2,6-dideoxy-d-xylo-4-hexulose 4-reductase activity, completing a pathway for UDP-d-QuiNAc synthesis in vitro. Background:d-QuiNAc is found in many important bacteria, but its biosynthesis has not been defined. Results: UDP-d-QuiNAc was synthesized in vitro from UDP-d-GlcNAc in reactions catalyzed by two cloned enzymes. Conclusion:R. etli CE3 protein WreQ has UDP-2-acetamido-2,6-dideoxy-d-xylo-4-hexulose 4-reductase activity. Significance: The defined pathway for UDP-d-QuiNAc biosynthesis provides this compound for in vitro biosynthetic studies and predicts organisms that contain d-QuiNAc.