Two polysaccharides were isolated from Escherichia coli O12, the major being identified as the O12-antigen and the minor as the K5-antigen. The polysaccharides were studied by sugar analysis, Smith degradation, and one- and two-dimensional (1)H and (13)C NMR spectroscopy. As a result, the following structure of the O12-polysaccharide was elucidated, which, to our knowledge, has not been hitherto found in bacterial carbohydrates: →2)-β-d-Glcp-(1→6)-α-d-GlcpNAc-(1→3)-α-l-FucpNAc-(1→3)-β-d-GlcpNAc-(1→. The →4)-β-d-GlcpA-(1→4)-α-d-GlcpNAc-(1→ structure established for the K5-polysaccharide (heparosan) is previously known. Functions of genes in the O-antigen biosynthesis gene cluster of E. coli O12 were assigned by comparison with sequences in the available databases and found to be consistent with the O12-polysaccharide structure.

Escherichia coli, glycosyltransferase, O-antigen gene cluster, O-Polysaccharide structure

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
2,2	Ac	175.7	23.2
2	aDGlcpN	99.0	55.2	72.3	71.3	73.5	61.8
	x?Ery-onic	?	82.3	74.5	61.7


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
2,2	Ac	-	2.04
2	aDGlcpN	5.11	3.94	3.78	3.50	3.89	3.79-3.86
	x?Ery-onic	-	3.97	4.25	3.72-3.76


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
2,2	Ac		23.2/2.04
2	aDGlcpN	99.0/5.11	55.2/3.94	72.3/3.78	71.3/3.50	73.5/3.89	61.8/3.79-3.86
	x?Ery-onic		82.3/3.97	74.5/4.25	61.7/3.72-3.76

The spectrum also has 1 signal at unknown position (not plotted).

There are 2 chemically distinct structures. Please, select:
Ac(1-2)aDGlcpN(1-2)xDEry?-onic Ac(1-2)aDGlcpN(1-2)xLEry?-onic

SVGMWSMILES3D molIonize

 

CC(=O)N[C@H]1[C@@H](O[C@@H](C(=O)O)[C@H](O)CO)O[C@H](CO)[C@@H](O)[C@@H]1O

339.297 g/mol (C₁₂H₂₁NO₁₀)