The
sialic acid-like
sugar 5,7-diacetamido-3,5,7,9-tetradeoxy-D-glycero-D-galacto-nonulosonic
acid, or legion-aminic
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 alpha2,4-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 11 candidate biosynthetic
enzymes from Campylobacter 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.