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 α2,4-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.

Campylobacter jejuni, sialic acid, legionaminic acid, flagellin glycosylation, neuraminic aid

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
2	Ac
4	Ac
	aDRhapN4N	94.0	53.8	67.7	54.8	68.1	18.0


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
2	Ac
4	Ac
	aDRhapN4N	5.11	4.30	4.06	3.77	3.97	1.19


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
2	Ac
4	Ac
	aDRhapN4N	94.0/5.11	53.8/4.30	67.7/4.06	54.8/3.77	68.1/3.97	18.0/1.19

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@@H]1[C@@H](O)O[C@H](C)[C@@H](NC(C)=O)[C@@H]1O

246.263 g/mol (C₁₀H₁₈N₂O₅)