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	C7	C8	C9
5,0,5	Ac
5,0,7	Ac
5,0	bXLegp	?	?	42.6	68.3	53.7	72.3	55.3	66.9	19.5
5	P
	xXnucC


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
5,0,5	Ac
5,0,7	Ac
5,0	bXLegp	-	-	1.63-2.48	3.98	3.72	4.33	3.77	4.03	1.10
5	P
	xXnucC


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
5,0,5	Ac
5,0,7	Ac
5,0	bXLegp			42.6/1.63-2.48	68.3/3.98	53.7/3.72	72.3/4.33	55.3/3.77	66.9/4.03	19.5/1.10
5	P
	xXnucC

The spectrum also has 2 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@@H]1[C@@H](O)C[C@@](OP(=O)(O)OC[C@H]2O[C@@H](n3ccc(N)nc3=O)[C@H](O)[C@@H]2O)(C(=O)O)O[C@H]1[C@H](NC(C)=O)[C@@H](C)O

639.508 g/mol (C₂₂H₃₄N₅O₁₅P)