Glycobiology Advance Access published online on March 12, 2009
Glycobiology, doi:10.1093/glycob/cwp039
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The CMP-legionaminic acid pathway in Campylobacter: biosynthesis involving novel GDP-linked precursors
Institute for Biological Sciences, National Research Council, Ottawa, Ontario, Canada K1A 0R6
1 To whom correspondence, proofs and reprints should be addressed; Fax: 613-952-9092 Tel: 613-991-2141 e-mail: ian.schoenhofen{at}nrc-cnrc.gc.ca
Received on December 18, 2008; accepted on March 7, 2009
The sialic acid-like sugar 5,7-diacetamido-3,5,7,9-tetradeoxy-D-glycero-D-galacto-nonulosonic acid, or legionaminic acid, is found as a virulence-associated cell-surface glycoconjugate in the Gram-negative bacteria Legionella pneumophila and Campylobacter coli. L. pneumophila serogroup 1 strains, causative agents of Legionnaire's disease, contain an
2,4-linked homopolymer of legionaminic acid within their lipopolysaccharide O-chains, whereas the gastrointestinal pathogen C. coli modifies its flagellin with this monosaccharide via O-linkage. In this work, we have purified and biochemically characterized eleven candidate biosynthetic enzymes from C. jejuni, thereby fully reconstituting the biosynthesis of legionaminic acid and its CMP-activated form, starting from fructose-6-P. This pathway involves unique GDP-linked intermediates, likely providing a cellular mechanism for differentiating between this and similar UDP-linked pathways, such as UDP-2,4-diacetamido-bacillosamine biosynthesis involved in N-linked protein glycosylation. Importantly, these findings provide a facile method for efficient large-scale synthesis of legionaminic acid, and since legionaminic acid and sialic acid share the same D-glycero-D-galacto absolute configuration, this sugar may now be evaluated for its potential as a sialic acid mimic.
Key words: Campylobacter jejuni / flagellin glycosylation / legionaminic acid / neuraminic acid / sialic acid