The whole-genome sequence of the multiply antibiotic resistant Acinetobacter baumannii isolate RCH51 belonging to sequence type ST103 (Institut Pasteur scheme) revealed that the set of genes at the capsule locus, KL24, includes four genes predicted to direct the synthesis of 3-acetamido-3,6-dideoxy-d-galactose (d-Fuc3NAc), and this sugar was found in the capsular polysaccharide (CPS). One of these genes, fdtE, encodes a novel bifunctional protein with an N-terminal FdtA 3,4-ketoisomerase domain and a C-terminal acetyltransferase domain. KL24 lacks a gene encoding a Wzy polymerase to link the oligosaccharide K units to form the CPS found associated with isolate RCH51, and a wzy gene was found in a small genomic island (GI) near the cpn60 gene. This GI is in precisely the same location as another GI carrying wzy and atr genes recently found in several A. baumannii isolates, but it does not otherwise resemble it. The CPS isolated from RCH51, studied by sugar analysis and 1D and 2D 1H and 13C NMR spectroscopy, revealed that the K unit has a branched pentasaccharide structure made up of Gal, GalNAc and GlcNAc residues with d-Fuc3NAc as a side branch, and the K units are linked via a β-d-GlcpNAc-(1→3)-β-d-Galp linkage formed by the Wzy encoded by the GI. The functions of the glycosyltransferases encoded by KL24 were assigned to formation of specific bonds. A correspondence between the order of the genes in KL24 and other KL and the order of the linkages they form was noted, and this may be useful in future predictions of glycosyltransferase specificities.

Acinetobacter baumannii, gene cluster, 6-dideoxy-D-galactose, polysaccharide structure, 3-Acetamido-3, capsule, antibiotic, Wzy polymerase, K locus, genomic island

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,6	aDGalp	99.6	68.9	80.6	70.3	71.8	62.3
3,4,2	Ac	175.5-175.9	23.3-23.7
3,4,3,3	Ac	175.5-175.9	23.3-23.7
3,4,3	bDFucp3N	104.9	69.7	56.1	71.1	73.3	16.7
3,4	aDGlcpN	99.7	54.0	81.7	69.8	72.2	66.6
3,2	Ac	175.5-175.9	23.3-23.7
3	aDGalpN	98.8	51.3	68.4	78.3	72.9	61.0
2	Ac	175.5-175.9	23.3-23.7
	bDGlcpN	103.6	55.8	80.3	72.2	76.9	61.8


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,6	aDGalp	4.94	3.89	3.93	4.19	3.96	3.72-3.72
3,4,2	Ac	-	2.05
3,4,3,3	Ac	-	2.05
3,4,3	bDFucp3N	4.54	3.54	3.93	3.65	3.90	1.25
3,4	aDGlcpN	4.98	4.15	3.96	3.75	4.34	3.64-4.30
3,2	Ac	-	2.05
3	aDGalpN	5.44	4.28	3.94	4.07	3.95	3.70-3.75
2	Ac	-	2.05
	bDGlcpN	4.76	3.83	3.78	3.68	3.45	3.75-3.90


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,6	aDGalp	99.6/4.94	68.9/3.89	80.6/3.93	70.3/4.19	71.8/3.96	62.3/3.72-3.72
3,4,2	Ac		23.3-23.7/2.05
3,4,3,3	Ac		23.3-23.7/2.05
3,4,3	bDFucp3N	104.9/4.54	69.7/3.54	56.1/3.93	71.1/3.65	73.3/3.90	16.7/1.25
3,4	aDGlcpN	99.7/4.98	54.0/4.15	81.7/3.96	69.8/3.75	72.2/4.34	66.6/3.64-4.30
3,2	Ac		23.3-23.7/2.05
3	aDGalpN	98.8/5.44	51.3/4.28	68.4/3.94	78.3/4.07	72.9/3.95	61.0/3.70-3.75
2	Ac		23.3-23.7/2.05
	bDGlcpN	103.6/4.76	55.8/3.83	80.3/3.78	72.2/3.68	76.9/3.45	61.8/3.75-3.90

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

958.918 g/mol (C₃₈H₆₂R₂N₄O₂₄, R = next and previous repeats, not counted in mol weight)