The O-antigen, consisting of many repeats of an oligosaccharide, is an essential component of the lipopolysaccharide on the surface of Gram-negative bacteria. The O-antigen is one of the most variable cell constituents, and different O-antigen forms are almost entirely due to genetic variations in O-antigen gene clusters. In this paper, we present structural and genetic evidence for a close relationship between Escherichia coli O107 and E. coli O117 O antigens. The O-antigen of E. coli O107 has a pentasaccharide repeating unit with the following structure: →4)-β-D-GalpNAc-(1→3)-α-L-Rhap-(1→4)-α-D-GlcpNAc-(1→4)-β-D-Galp-(1→3)-α-D-GalpNAc-(1→, which differs from the known repeating unit of E. coli O117 only in the substitution of D-GlcNAc for D-Glc. The O-antigen gene clusters of E. coli O107 and O117 share 98.6% overall DNA identity and contain the same set of genes in the same organization. It is proposed that one cluster was evolved from another via mutations, and the substitution of a few amino acids residues in predicted glycosyltransferases resulted in the functional change of one such protein for transferring different sugars in O107 (D-GlcNAc) and O117 (D-Glc), leading to different O-antigen structures. This is an example of the O-antigen alteration caused by nucleotide mutations, which is less commonly reported for O-antigen variations.

Lipopolysaccharide, O-antigen, Escherichia coli O107, Escherichia coli O117

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,4,3,2	Ac	175.7	23.3
3,4,4,3	bDGalpN	105.4	54.1	70.7	77.4	76.8	61.6
3,4,4	aLRhap	101.9	71.8	81.4	72.2	70.8	17.9
3,4,2	Ac	176.7	23.7
3,4	aDGlcpN	99.9	55.6	70.9	78.9	72.5	61.2
3	bDGalp	106.3	71.9	73.4	78.7	76.6	61.7
2	Ac	175.7	23.3
	aDGalpN	100.2	50.3	78.1	70.0	71.7	61.6


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,4,3,2	Ac	-	2.04
3,4,4,3	bDGalpN	4.69	4.01	3.83	4.02	3.74	3.70-3.70
3,4,4	aLRhap	4.90	4.18	3.84	3.52	4.02	1.24
3,4,2	Ac	-	2.08
3,4	aDGlcpN	4.87	3.93	3.85	3.68	4.25	3.75-3.75
3	bDGalp	4.58	3.55	3.72	3.97	3.74	3.74-3.74
2	Ac	-	2.04
	aDGalpN	4.96	4.43	4.21	4.28	4.45	3.70-3.72


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,4,3,2	Ac		23.3/2.04
3,4,4,3	bDGalpN	105.4/4.69	54.1/4.01	70.7/3.83	77.4/4.02	76.8/3.74	61.6/3.70-3.70
3,4,4	aLRhap	101.9/4.90	71.8/4.18	81.4/3.84	72.2/3.52	70.8/4.02	17.9/1.24
3,4,2	Ac		23.7/2.08
3,4	aDGlcpN	99.9/4.87	55.6/3.93	70.9/3.85	78.9/3.68	72.5/4.25	61.2/3.75-3.75
3	bDGalp	106.3/4.58	71.9/3.55	73.4/3.72	78.7/3.97	76.6/3.74	61.7/3.74-3.74
2	Ac		23.3/2.04
	aDGalpN	100.2/4.96	50.3/4.43	78.1/4.21	70.0/4.28	71.7/4.45	61.6/3.70-3.72

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

917.865 g/mol (C₃₆H₅₉R₂N₃O₂₄, R = next and previous repeats, not counted in mol weight)