The O-antigen of the lipopolysaccharide (LPS) from the enteroaggregative Escherichia coli strain 87/D2 has been determined by component analysis together with NMR spectroscopy. The polysaccharide has pentasaccharide repeating units in which all the residues have the galacto-configuration. The repeating unit of the O-antigen, elucidated using the O-deacylated LPS, is branched with the following structure: Analysis of the (1)H NMR spectrum of the LPS revealed O-acetyl groups (approximately 0.7 per repeating unit) distributed over two positions. Subsequent analysis showed that the galactose residue carries acetyl groups at either O-3 or O-4 in a ratio of approximately 2:1. The international reference strain from E. coli O128ab was investigated and the repeating unit of the O-antigens has the following structure: Analysis of the (1)H NMR spectrum of the LPS revealed O-acetyl groups (approximately one per repeating unit) distributed over two positions. The integrals of the resonances for the O-acetyl groups indicated similarities between the O-antigen from E. coli O128ab and that of E. coli strain 87/D2, whereas the O-acetyl substitution pattern in the E. coli O128ac O-antigen differed slightly. Enzyme immunoassay using specific anti-E. coli O128ab and anti-E. coli O128ac rabbit sera confirmed the results

Lipopolysaccharide, NMR, Escherichia coli, serology, biological repeating unit, Enteroaggregative

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,3,2	aLFucp	100.0	68.9	70.5	72.7	67.7	16.2
3,4,3	bDGalp	103.0	76.8	74.4	69.7	73.6	68.8
3,4,2	Ac	175.1	23.2
3,4	bDGalpN	104.6	52.4	77.6	69.3	75.5	62.0
3	aDGalp	96.6	69.5	69.7	77.7	71.4	61.0
2	Ac	175.1	23.2
	bDGalpN	102.2	51.6	76.8	65.0	75.8	62.0


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,3,2	aLFucp	5.23	3.76	3.62	3.70	4.21	1.20
3,4,3	bDGalp	4.61	3.62	3.82	3.88	3.77	3.88-3.94
3,4,2	Ac	-	2.05
3,4	bDGalpN	4.48	3.97	3.89	4.03	3.70	3.80
3	aDGalp	5.08	3.64	3.88	4.01	3.80	3.70-3.86
2	Ac	-	2.05
	bDGalpN	4.57	4.04	3.81	4.06	3.68	3.80


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,3,2	aLFucp	100.0/5.23	68.9/3.76	70.5/3.62	72.7/3.70	67.7/4.21	16.2/1.20
3,4,3	bDGalp	103.0/4.61	76.8/3.62	74.4/3.82	69.7/3.88	73.6/3.77	68.8/3.88-3.94
3,4,2	Ac		23.2/2.05
3,4	bDGalpN	104.6/4.48	52.4/3.97	77.6/3.89	69.3/4.03	75.5/3.70	62.0/3.80
3	aDGalp	96.6/5.08	69.5/3.64	69.7/3.88	77.7/4.01	71.4/3.80	61.0/3.70-3.86
2	Ac		23.2/2.05
	bDGalpN	102.2/4.57	51.6/4.04	76.8/3.81	65.0/4.06	75.8/3.68	62.0/3.80

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*OC[C@H]1O[C@@H](O[C@@H]2[C@@H](NC(C)=O)[C@H](O[C@H]3[C@@H](CO)O[C@H](O[C@@H]4[C@@H](NC(C)=O)[C@H](*)O[C@H](CO)[C@@H]4O)[C@H](O)[C@H]3O)O[C@H](CO)[C@@H]2O)[C@H](O[C@@H]2O[C@@H](C)[C@@H](O)[C@@H](O)[C@@H]2O)[C@@H](O)[C@H]1O

876.812 g/mol (C₃₄H₅₆R₂N₂O₂₄, R = next and previous repeats, not counted in mol weight)