Infections caused by Acinetobacter baumannii isolates from the major global clones, GC1 and GC2, are difficult to treat with antibiotics, and phage therapy, which requires extensive knowledge of the variation in the surface polysaccharides, is an option under consideration. The gene clusters directing the synthesis of capsular polysaccharide (CPS) in A. baumannii GC1 isolate A388 and GC2 isolate G21 differ by a single glycosyltransferase (gtr) gene. They include genes encoding a novel UDP-glucose dehydrogenase (Ugd2) and a putative pyruvyl transferase (Ptr2). The composition and structures of the linear K20 and K21 tetrasaccharide repeats (K units) of the CPSs isolated from A338 and G21, respectively, were established by sugar analyses and Smith degradation along with 1D and 2D 1H and 13C NMR spectroscopy. The K20 and K21 CPSs are the first known to include GlcpA produced by Ugd2 and d-galactose with an (R)-configured 4,6-pyruvic acid acetal added by Prt2. The first sugar in the tetrasaccharide K units is 2-acetamido-4-amino-2,4,6-trideoxy-d-glucose (d-QuipNAc4N) that carries a 4-N-[(S)-3-hydroxybutanoyl] group in some K units and a 4-N-acetyl group in the others. Accordingly, K unit polymerases WzyK20 and WzyK21 form a β-d-QuipNAc4NR-(1→2)-d-Galp bond. The K20 and K21 units differ only in the configuration of the glycosidic linkages of d-GlcpNAc allowing the unique inverting glycosyltransferases Gtr43 and the retaining glycosyltransferase Gtr45 to be assigned to the formation of the β-d-GlcpNAc-(1→4)-d-GlcpA and α-d-GlcpNAc-(1→4)-d-GlcpA linkages, respectively.

Acinetobacter baumannii, capsular polysaccharide, glucuronic acid, Pyruvic acid acetal, K locus

← originally published structure   Show legend

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3,2,4	lS3HOBut	175.4	46.5	66.4	23.6
3,3,2,2	Ac	174.6-176.0	23.4-24.1
3,3,2	bDQuipN4N	102.7	57.8	73.0	62.0	72.3	18.3
3,3,6	xRPyr	175.4	101.4	26.4
3,3	bDGalp	99.3	78.4	72.6	72.3	67.3	66.3
3,2	Ac	174.6-176.0	23.4-24.1
3	bDGlcpN	102.7	55.9	83.9	69.8	76.9	62.0
	xLEry-onic	104.6	71.8	82.3	62.0


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,2,4	lS3HOBut	-	2.42	4.18	1.21
3,3,2,2	Ac	-	1.92-1.94
3,3,2	bDQuipN4N	4.77	3.77	3.58	3.61	3.54	1.22
3,3,6	xRPyr	-	-	1.48
3,3	bDGalp	4.61	3.61	3.68	4.17	3.61	3.93-4.05
3,2	Ac	-	1.92-1.94
3	bDGlcpN	4.76	3.82	3.76	3.58	3.48	3.77-3.91
	xLEry-onic	-	4.34	4.33	3.77-4.06


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3,2,4	lS3HOBut		46.5/2.42	66.4/4.18	23.6/1.21
3,3,2,2	Ac		23.4-24.1/1.92-1.94
3,3,2	bDQuipN4N	102.7/4.77	57.8/3.77	73.0/3.58	62.0/3.61	72.3/3.54	18.3/1.22
3,3,6	xRPyr			26.4/1.48
3,3	bDGalp	99.3/4.61	78.4/3.61	72.6/3.68	72.3/4.17	67.3/3.61	66.3/3.93-4.05
3,2	Ac		23.4-24.1/1.92-1.94
3	bDGlcpN	102.7/4.76	55.9/3.82	83.9/3.76	69.8/3.58	76.9/3.48	62.0/3.77-3.91
	xLEry-onic		71.8/4.34	82.3/4.33	62.0/3.77-4.06

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@H]1[C@H](O[C@@H]2[C@@H](O)[C@H]3O[C@](C)(C(=O)O)OC[C@H]3O[C@H]2O[C@H]2[C@H](O)[C@@H](CO)O[C@@H](O[C@@H](CO)[C@H](O)C(=O)O)[C@@H]2NC(C)=O)O[C@H](C)[C@@H](NC(=O)C[C@H](C)O)[C@@H]1O

843.786 g/mol (C₃₃H₅₃N₃O₂₂)