The structure of the repeating unit of the O-antigenic polysaccharide from Plesiomonas shigelloides strain AM36565 has been determined. Component analysis and (1)H and (13)C NMR spectroscopy experiments were employed to elucidate the structure. Inter-residue correlations were determined by (1)H,(13)C heteronuclear multiple-bond correlation, (1)H,(1)H-NOESY, and (1)H,(13)C-HSQC-(1)H,(1)H-NOESY experiments. The O-antigen polysaccharide is composed of repeating units with the following structure: →3)-α-L-Rhap-(1→2)-α-L-Rhap-(1→4)[β-D-GalpNAc-(1→3)]-α-d-GlcpNAc-(1→, in which the monosaccharide side-chain substitutes the backbone in half of the repeating units. A matrix-assisted laser desorption/ionization mass spectrometry experiment suggested that the polysaccharide consists of two regions, one with tetrasaccharide repeating units and one with trisaccharide repeating units.

Lipopolysaccharide, NMR, biological repeating unit, MALDI-TOF MS, Plesiomonas shigelloides, SDS-PAGE

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
4,2	aLRhap	103.0	67.6	76.1	71.2	70.1	17.7
4	aLRhap	98.4	79.7	70.5	73.4	69.6	17.7
2	Ac	174.5	23.0
3,2	Ac	175.6	23.2
3	%bDGalpN	103.1	53.5	71.2	68.8	75.8	62.0
	aDGlcpN	95.1	54.5	75.1	72.4	72.0	60.6


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
4,2	aLRhap	4.99	4.23	3.81	3.54	3.78	1.33
4	aLRhap	5.15	3.96	4.02	3.44	4.61	1.38
2	Ac	-	2.11
3,2	Ac	-	1.99
3	%bDGalpN	4.56	3.84	3.76	3.93	3.63	3.80-3.86
	aDGlcpN	4.97	4.13	4.14	3.86	4.07	3.70-3.87


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
4,2	aLRhap	103.0/4.99	67.6/4.23	76.1/3.81	71.2/3.54	70.1/3.78	17.7/1.33
4	aLRhap	98.4/5.15	79.7/3.96	70.5/4.02	73.4/3.44	69.6/4.61	17.7/1.38
2	Ac		23.0/2.11
3,2	Ac		23.2/1.99
3	%bDGalpN	103.1/4.56	53.5/3.84	71.2/3.76	68.8/3.93	75.8/3.63	62.0/3.80-3.86
	aDGlcpN	95.1/4.97	54.5/4.13	75.1/4.14	72.4/3.86	72.0/4.07	60.6/3.70-3.87

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

698.672 g/mol (C₂₈H₄₆R₂N₂O₁₈, R = next and previous repeats, not counted in mol weight)