Gene clusters for biosynthesis of 24 of 34 basic O-antigen forms of Shigella spp. are identical or similar to those of the genetically closely related bacterium Escherichia coli. For 18 of these relatedness was confirmed chemically by elucidation of the O-antigen (O-polysaccharide) structures. In this work, structures of the six remaining O-antigens of E. coli O32, O53, O79, O105, O183 (all related to S. boydii serotypes), and O38 (related to S. dysenteriae type 8) were established using (1)H and (13)C NMR spectroscopy. They were found to be identical to the Shigella counterparts, except for the O32- and O38-polysaccharides, which differ in the presence of O-acetyl groups. The structure of the E. coli O105-related O-polysaccharide of S. boydii type 11 proposed earlier is revised. The contents of the O-antigen gene clusters of the related strains of E. coli and Shigella spp. and different mechanisms of O-antigen diversification in these bacteria are discussed in view of the O-polysaccharide structures established. These data illustrate the value of the O-antigen chemistry and genetics for elucidation of evolutionary relationships of bacteria.

Escherichia coli, Shigella dysenteriae, Shigella boydii, O-antigen gene cluster, O-Polysaccharide structure

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
4,4,6,4	aDGalp	99.9	69.8	70.4	69.5	69.3	68.0
4,4,6	bDGlcpA	104.2	74.2	77.7	77.6	78.1	175.9
4,4	bDGalp	105.3	72.6	74.0	69.9	74.9	71.1
4	bDGalp	104.2	72.5	74.2	78.1	75.7	62.0
2	Ac	176.3	23.5
	bDGlcpN	102.5	56.3	73.7	79.8	76.0	61.4


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
4,4,6,4	aDGalp	5.48	3.80	3.80	3.87	3.97	3.73-3.94
4,4,6	bDGlcpA	4.52	3.37	3.77	3.78	3.81	-
4,4	bDGalp	4.59	3.58	3.68	3.93	3.88	3.93-4.02
4	bDGalp	4.52	3.65	3.81	4.22	3.78	3.80-3.85
2	Ac	-	2.08
	bDGlcpN	4.78	3.78	3.79	3.72	3.71	3.86-4.04


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
4,4,6,4	aDGalp	99.9/5.48	69.8/3.80	70.4/3.80	69.5/3.87	69.3/3.97	68.0/3.73-3.94
4,4,6	bDGlcpA	104.2/4.52	74.2/3.37	77.7/3.77	77.6/3.78	78.1/3.81	
4,4	bDGalp	105.3/4.59	72.6/3.58	74.0/3.68	69.9/3.93	74.9/3.88	71.1/3.93-4.02
4	bDGalp	104.2/4.52	72.5/3.65	74.2/3.81	78.1/4.22	75.7/3.78	62.0/3.80-3.85
2	Ac		23.5/2.08
	bDGlcpN	102.5/4.78	56.3/3.78	73.7/3.79	79.8/3.72	76.0/3.71	61.4/3.86-4.04

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*OC[C@H]1O[C@H](O[C@H]2[C@H](O)[C@@H](O)[C@H](OC[C@H]3O[C@@H](O[C@@H]4[C@H](O)[C@@H](O)[C@H](O[C@H]5[C@H](O)[C@@H](NC(C)=O)[C@H](*)O[C@@H]5CO)O[C@@H]4CO)[C@H](O)[C@@H](O)[C@H]3O)O[C@@H]2C(=O)O)[C@H](O)[C@@H](O)[C@H]1O

865.741 g/mol (C₃₂H₅₁R₂NO₂₆, R = next and previous repeats, not counted in mol weight)