The repeat unit structure of the K2 capsule from an extensively antibiotic-resistant Acinetobacter baumannii global clone 2 (GC2) strain was determined. The oligosaccharide contains three simple sugars, d-glucopyranose, d-galatopyranose and N-acetyl-d-galactosamine, and the complex sugar, 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic acid (Pse5Ac7Ac or pseudaminic acid), which has not previously been reported in any A. baumannii capsule. The strain was found to carry all the genes required for the synthesis of the sugars and construction of the K2 structure. The linkages catalyzed by the initiating transferase, three glycosyltransferases and the Wzy polymerase were also predicted. Examination of publicly available A. baumannii genome sequences revealed that the same gene cluster, KL2, often occurs in extensively antibiotic-resistant GC2 isolates and in further strain types. The gene module responsible for the synthesis of pseudaminic acid was also detected in four other K loci. A related module including genes for an acylated relative of pseudaminic acid was also found in two new KL types. A polymerase chain reaction scheme was developed to detect all modules containing genes for sugars based on pseudaminic acid and to specifically detect KL2.

Acinetobacter baumannii, capsule polysaccharide, K locus, global clone 2, K2

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9
3,6,6,5	Ac
3,6,6,7	Ac
3,6,6	aXPsep	?	?	36.6	66.1	50.0	71.8	54.9	68.1	16.9
3,6	bDGlcp	104.8	74.4	76.9	70.5	76.0	63.4
3	bDGalp	105.9	71.1	82.7	69.8	74.5	71.1
2	Ac
	bDGalpN	104.2	52.7	80.7	69.4	76.0	62.3


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
3,6,6,5	Ac
3,6,6,7	Ac
3,6,6	aXPsep	-	-	1.60-2.15	4.26	4.23	3.85	4.20	4.24	1.15
3,6	bDGlcp	4.47	3.28	3.46	3.54	3.53	3.53-3.67
3	bDGalp	4.48	3.59	3.72	4.15	3.86	3.86-3.98
2	Ac
	bDGalpN	4.68	4.05	3.90	4.19	3.70	3.78-3.78


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
3,6,6,5	Ac
3,6,6,7	Ac
3,6,6	aXPsep			36.6/1.60-2.15	66.1/4.26	50.0/4.23	71.8/3.85	54.9/4.20	68.1/4.24	16.9/1.15
3,6	bDGlcp	104.8/4.47	74.4/3.28	76.9/3.46	70.5/3.54	76.0/3.53	63.4/3.53-3.67
3	bDGalp	105.9/4.48	71.1/3.59	82.7/3.72	69.8/4.15	74.5/3.86	71.1/3.86-3.98
2	Ac
	bDGalpN	104.2/4.68	52.7/4.05	80.7/3.90	69.4/4.19	76.0/3.70	62.3/3.78-3.78

The spectrum also has 2 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]O[C@H]1[C@@H](O)[C@@H](CO[C@@H]2O[C@H](CO[C@@]3(C(=O)O)C[C@H](O)[C@H](NC(C)=O)[C@H]([C@@H](NC(C)=O)[C@H](C)O)O3)[C@@H](O)[C@H](O)[C@H]2O)O[C@@H](O[C@@H]2[C@@H](NC(C)=O)[C@H]([*])O[C@H](CO)[C@@H]2O)[C@@H]1O

843.786 g/mol (C₃₃H₅₃R₂N₃O₂₂, R = next and previous repeats, not counted in mol weight)