The structure of the O-antigen from Escherichia coli reference strain O188 (E. coli O188:H10) has been investigated. The lipopolysaccharide shows a typical nonrandom modal chain-length distribution and the sugar and absolute configuration analysis revealed d-Man, d-Glc, d-GlcN and d-GlcA as major components. The structure of the O-specific polysaccharide was determined using one- and two-dimensional (1)H and (13)C NMR spectroscopy experiments, where inter-residue correlations were identified by (1)H,(13)C-heteronuclear multiple-bond correlation and (1)H,(1)H-NOESY experiments, which revealed that it consists of pentasaccharide repeating units with the following structure: Biosynthetic aspects and NMR analysis are consistent with the presented structure as the biological repeating unit. The O-antigen of Shigella boydii type 16 differs only in that it carries O-acetyl groups to ~50% at O6 of the branch-point mannose residues. A molecular model of the E. coli O188 O-antigen containing 20 repeating units extends ~100 A, which is similar to the height of the periplasmic portion of polysaccharide co-polymerase Wzz proteins that regulate the O-antigen chain length of lipopolysaccharides in the Wzx/Wzy biosynthetic pathway.

Lipopolysaccharide, Escherichia coli, NMR spectroscopy, Shigella boydii

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,2	bDGlcpA	104.95	73.93	74.46	81.62	77.77	174.18
3,4,3	aDGalp	101.44	69.50	70.14	70.47	72.52	62.74
3,4	bDManp	101.25	79.26	78.06	67.22	77.18	61.19
3	bDManp	101.64	71.11	72.18	77.53	75.78	61.31
2	Ac	175.40	23.27
	bDGlcpN	101.59	55.25	84.36	69.37	76.21	61.48


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,2	bDGlcpA	4.61	3.43	3.60	3.79	3.65	-
3,4,3	aDGalp	5.26	3.79	3.83	3.99	4.17	3.74
3,4	bDManp	4.80	4.35	3.84	3.81	3.48	3.80-3.93
3	bDManp	4.71	3.93	3.80	3.81	3.54	3.72-3.87
2	Ac	-	2.07
	bDGlcpN	4.61	3.84	3.75	3.59	3.53	3.79-3.94


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,2	bDGlcpA	104.95/4.61	73.93/3.43	74.46/3.60	81.62/3.79	77.77/3.65	
3,4,3	aDGalp	101.44/5.26	69.50/3.79	70.14/3.83	70.47/3.99	72.52/4.17	62.74/3.74
3,4	bDManp	101.25/4.80	79.26/4.35	78.06/3.84	67.22/3.81	77.18/3.48	61.19/3.80-3.93
3	bDManp	101.64/4.71	71.11/3.93	72.18/3.80	77.53/3.81	75.78/3.54	61.31/3.72-3.87
2	Ac		23.27/2.07
	bDGlcpN	101.59/4.61	55.25/3.84	84.36/3.75	69.37/3.59	76.21/3.53	61.48/3.79-3.94

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

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