The structure of the O-antigen polysaccharide (PS) from Escherichia coli O177 has been determined. Component analysis together with (1)H and (13)C NMR spectroscopy experiments was used to determine the structure. Inter-residue correlations were determined by (1)H,(13)C-heteronuclear multiple-bond correlation and (1)H,(1)H-NOESY experiments. PS is composed of tetrasaccharide repeating units with the following structure: →2)-α-L-Rhap-(1→3)-α-L-FucpNAc-(1→3)-α-L-FucpNAc-(1→3)-β-D-GlcpNAc-(1→. An α-L-Rhap residue is suggested to be present at the terminal part of the polysaccharide, which on average is composed of ∼20 repeating units, since the (1)H and (13)C chemical shifts of an α-linked rhamnopyranosyl group could be assigned by a combination of 2D NMR spectra. Consequently, the biological repeating unit has a 3-substituted N-acetyl-D-glucosamine residue at its reducing end. The repeating unit of the E. coli O177 O-antigen shares the →3)-α-L-FucpNAc-(1→3)-β-D-GlcpNAc-(1→ structural element with the O-antigen from E. coli O15 and this identity may then explain the reported cross-reactivity between the strains.

Lipopolysaccharide, NMR, Escherichia coli, cross-reactivity, biological repeating unit

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3,3	aLRhap	95.78	79.72	70.56	72.90	70.07	17.58
3,3,2	Ac	174.96	22.89
3,3	aLFucpN	94.19	47.92	73.17	67.53	67.84	16.36
3,2	Ac	174.85	23.07
3	aLFucpN	98.69	48.06	73.22	67.80	67.44	16.11
2	Ac	175.10	23.04
	bDGlcpN	103.35	56.41	79.57	69.24	76.51	61.58


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,3	aLRhap	5.08	4.00	3.72	3.31	3.56	1.30
3,3,2	Ac	-	2.04
3,3	aLFucpN	5.01	4.33	3.76	4.02	3.90	1.29
3,2	Ac	-	2.06
3	aLFucpN	5.03	4.37	3.91	3.99	4.35	1.20
2	Ac	-	2.00
	bDGlcpN	4.66	3.93	3.69	3.54	3.47	3.75-3.92


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3,3	aLRhap	95.78/5.08	79.72/4.00	70.56/3.72	72.90/3.31	70.07/3.56	17.58/1.30
3,3,2	Ac		22.89/2.04
3,3	aLFucpN	94.19/5.01	47.92/4.33	73.17/3.76	67.53/4.02	67.84/3.90	16.36/1.29
3,2	Ac		23.07/2.06
3	aLFucpN	98.69/5.03	48.06/4.37	73.22/3.91	67.80/3.99	67.44/4.35	16.11/1.20
2	Ac		23.04/2.00
	bDGlcpN	103.35/4.66	56.41/3.93	79.57/3.69	69.24/3.54	76.51/3.47	61.58/3.75-3.92

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

723.726 g/mol (C₃₀H₄₉R₂N₃O₁₇, R = next and previous repeats, not counted in mol weight)