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Identification and characterization of NeuB3 from Campylobacter jejuni as a pseudaminic acid synthase

TitleIdentification and characterization of NeuB3 from Campylobacter jejuni as a pseudaminic acid synthase
Publication TypeJournal Article
Year of Publication2005
AuthorsChou, WK, Dick, S, Wakarchuk, WW, Tanner, ME
JournalJournal of Biological Chemistry
Volume280
Pagination35922-35928
Date PublishedOct
Type of ArticleArticle
ISBN Number0021-9258
KeywordsBISUBSTRATE INHIBITOR, ESCHERICHIA-COLI, HELICOBACTER-PYLORI, KDO8P SYNTHASE, NEISSERIA-MENINGITIDIS, O-SPECIFIC POLYSACCHARIDE, PNEUMOPHILA SEROGROUP-1 LIPOPOLYSACCHARIDE, PSEUDOMONAS-AERUGINOSA, SIALIC ACIDS, SOMATIC ANTIGENS
Abstract

Campylobacter jejuni and Campylobacter coli are the main causes of bacterial diarrhea worldwide, and Helicobacter pylori is known to cause duodenal ulcers. In all of these pathogenic organisms, the flagellin proteins are heavily glycosylated with a 2-keto-3-deoxy acid, pseudaminic acid (5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L- manno-nonulosonic acid). The presence of pseudaminic acid is required for the proper development of the flagella and is thereby necessary for motility in, and invasion of, the host. In this study we report the first characterization of NeuB3 from C. jejuni as a pseudaminic acid synthase; the enzyme directly responsible for the biosynthesis of pseudaminic acid. Pseudaminic acid synthase catalyzes the condensation of phosphoenolpyruvate ( PEP) with the hexose, 2,4-diacetamido-2,4,6- trideoxy-L-altrose (6-deoxy-AltdiNAc), to form pseudaminic acid and phosphate. The enzymatic activity was monitored using H-1 and P-31 NMR spectroscopy, and the product was isolated and characterized. Kinetic analysis reveals that pseudaminic acid synthase requires the presence of a divalent metal ion for catalysis and that optimal catalysis occurs at pH 7.0. A coupled enzymatic assay gave the values for k(cat) of 0.65 +/- 0.01 s(-1), KmPEP of 6.5 +/- 0.4 mu M, and K(m)6-deoxy- AltdiNAc of 9.5 +/- 0.7 mu M. A mechanistic study on pseudaminic acid synthase, using[2-O-18] PEP, shows that catalysis proceeds through a C-O bond cleavage mechanism similar to other PEP condensing synthases such as sialic acid synthase.

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