Based on the O-antigens (O-polysaccharides), one of the most variable cell constituents, 46 O-serogroups have been recognized in the Kauffmann-White serotyping scheme for Salmonella enterica. In this work, the structure of the O-polysaccharide and the genetic organization of the O-antigen gene cluster of S. enterica O56 were investigated. As judged by sugar and methylation analyses, along with NMR spectroscopic data, the O-polysaccharide has a linear tetrasaccharide O-unit, which consists of one residue each of d-ribofuranose, N-acetyl-d-glucosamine, N-acetyl-d-galactosamine, and a novel sugar derivative, 4-(N-acetyl-l-seryl)amino-4,6-dideoxy-d-glucose (d-Qui4NSerAc). The following structure of the O-polysaccharide was established: →3)-β-D-Quip4NSerAc-(1→3)-β-D-Ribf-(1→4)-α-D-GalpNAc-(1→3)-α-D-GlcpNAc-(1→ The O-antigen gene cluster of S. enterica O56 having 12 open reading frames was found between the housekeeping genes galF and gnd. A comparison with databases and using the O-antigen structure data enabled us to ascribe functions to genes for (i) synthesis of d-GalNAc and d-Qui4NSerAc, (ii) sugar transfer, and (iii) O-antigen processing, including genes for O-unit flippase (Wzx) and O-antigen polymerase (Wzy).

O-antigen, Salmonella enterica, 6-dideoxy-d-glucose, 4-amino-4, O-antigen gene cluster, bacterial polysaccharide srtructure

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,3,4,2	Ac	175.5	23.2
3,4,3,4	xLSer	173.4	57.4	62.3
3,4,3	bDQuip4N	104.3	73.6	77.8	58.0	72.2	18.0
3,4	bDRibf	110.1	75.8	80.6	82.2	64.0
3,2	Ac	176.0	23.5
3	aDGalpN	98.5	51.2	69.2	77.0	72.1	61.2
2	Ac	175.0	23.9
	aDGlcpN	97.8	53.1	77.0	72.2	73.0	62.4


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,3,4,2	Ac	-	2.02
3,4,3,4	xLSer	-	4.33	3.71-3.82
3,4,3	bDQuip4N	4.53	3.47	3.82	3.87	3.57	1.18
3,4	bDRibf	5.28	4.36	4.25	4.13	3.72-3.87
3,2	Ac	-	2.04
3	aDGalpN	5.47	4.17	3.84	4.07	3.82	3.79-3.79
2	Ac	-	2.05
	aDGlcpN	5.15	3.90	3.87	3.72	4.15	3.75-3.81


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,3,4,2	Ac		23.2/2.02
3,4,3,4	xLSer		57.4/4.33	62.3/3.71-3.82
3,4,3	bDQuip4N	104.3/4.53	73.6/3.47	77.8/3.82	58.0/3.87	72.2/3.57	18.0/1.18
3,4	bDRibf	110.1/5.28	75.8/4.36	80.6/4.25	82.2/4.13	64.0/3.72-3.87
3,2	Ac		23.5/2.04
3	aDGalpN	98.5/5.47	51.2/4.17	69.2/3.84	77.0/4.07	72.1/3.82	61.2/3.79-3.79
2	Ac		23.9/2.05
	aDGlcpN	97.8/5.15	53.1/3.90	77.0/3.87	72.2/3.72	73.0/4.15	62.4/3.75-3.81

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

812.776 g/mol (C₃₂H₅₂R₂N₄O₂₀, R = next and previous repeats, not counted in mol weight)