Fusobacterium nucleatum is an anaerobic bacterium found in the human mouth where it causes periodontitis. Recently, it has been gaining attention as a potential causative agent for colorectal cancer and is strongly linked with pregnancy complications including pre-term and still births. Little is known about virulence factors of this organism and thus we have initiated studies to examine the bacterial surface glycochemistry. Consistent with a recent paper suggesting that F. nucleatum strain 10593 can synthesize sialic acid, a staining technique identified sialic acid on the bacterial surface. We isolated lipopolysaccharide from this F. nucleatum strain and performed structural analysis on the O-antigen. Our studies identified a trisaccharide repeating unit of the O-antigen with the following structure: -[→4)-α-Neup5Ac-(2→4)-β-d-Galp-(1→3)-α-d-FucpNAc4NAc-(1-]- where Ac indicates 4-N-acetylation of approximately 30% FucNAc4N residues. The presence of sialic acid as a constituent of the O-antigen is consistent with recent data identifying de novo sialic acid synthesis in this strain.

Lipopolysaccharide, sialic acid, Fusobacterium, Fusobacterium nucleatum

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9
3,4,5	Ac	?	23.3
3,4	aXNeup	173.8	101.9	37.6	75.7	50.4	74.0	69.0	73.0	63.9
3	bDGalp	106.2	72.2	72.9	73.4	76.3	62.1
2	Ac	?	23.3
4	30%Ac	?	23.3
	aDFucpN4N	95.4	49.6	77.5	54.4	67.3	16.8


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
3,4,5	Ac	-	2.02-2.06
3,4	aXNeup	-	-	1.77-2.82	3.69	4.04	3.71	3.62	3.85	3.63-3.86
3	bDGalp	4.50	3.52	3.60	4.49	3.70	3.64-3.73
2	Ac	-	2.02-2.06
4	30%Ac	-	2.02-2.06
	aDFucpN4N	5.00	4.33	3.97	4.47	4.06	1.11


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
3,4,5	Ac		23.3/2.02-2.06
3,4	aXNeup			37.6/1.77-2.82	75.7/3.69	50.4/4.04	74.0/3.71	69.0/3.62	73.0/3.85	63.9/3.63-3.86
3	bDGalp	106.2/4.50	72.2/3.52	72.9/3.60	73.4/4.49	76.3/3.70	62.1/3.64-3.73
2	Ac		23.3/2.02-2.06
4	30%Ac		23.3/2.02-2.06
	aDFucpN4N	95.4/5.00	49.6/4.33	77.5/3.97	54.4/4.47	67.3/4.06	16.8/1.11

The spectrum also has 3 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]O[C@H]1C[C@](O[C@H]2[C@@H](CO)O[C@@H](O[C@@H]3[C@@H](NC(C)=O)[C@@H]([*])O[C@H](C)[C@@H]3NC(C)=O)[C@H](O)[C@H]2O)(C(=O)O)O[C@@H]([C@H](O)[C@H](O)CO)[C@@H]1NC(C)=O

681.645 g/mol (C₂₇H₄₃R₂N₃O₁₇, R = next and previous repeats, not counted in mol weight)