The primary structure of the O-deacetylated capsular glucuronoxylomannan (GXM) isolated from Cryptococcus neoformans serotype C was investigated by 2D NMR spectroscopy. Assignment of the 1H NMR chemical shifts for the polysaccharide was accomplished from the analysis of DQF-COSY, TOCSY, NOESY and/or ROESY spectra of three isolates (298, 34, and 401). These isolates contain the same polysaccharide glycosyl residues but in different proportions. The serotype C GXM consists of two repeating polysaccharide units that have the following structures: . It is not known if these repeating units comprise a single or two separate polymer chains. The relative amounts of the more highly branched octasaccharide 1 in the isolates studied (i.e., approximately 75% in isolate 34, 50% in isolate 298, and 25% in isolate 401) can be used to explain the serological specificity of these isolates with C. neoformans factor sera, as was previously determined by ELISA in this laboratory. The octasaccharide 1 component is the one previously postulated as the structure of the serotype C GXM although definitive placement of the b-Xyl-(l→4) residues had previously not been determined. The heptasaccharide 2 component is uniformly found as the repeating unit in the polysaccharide from serotype B isolates. Additionally, GXM 401 was found to contain a small amount of the hexasaccharide repeating unit usually attributed to serotype A GXM.

NMR, structure, capsular, serotype, capsular polysaccharide, spectroscopy, 2D NMR spectroscopy, O-acetyl, 1H NMR, Cryptococcus, Cryptococcus neoformans, Glucuronoxylomannan

13C NMR data:
missing...
1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,2	bDGlcpA	4.452	3.412	3.482	3.598	3.630	-
3,3,4	bDXylp	4.401	3.274	3.459	?	?
3,3	aDManp	5.118	4.266	4.178	3.661	3.978	3.784-3.873
3,2	bDXylp	4.484	3.290	3.457	3.632	?
3	aDManp	5.311	4.188	4.079	3.856	3.870	?
2	bDXylp	4.266	3.342	3.415	3.674	?
	aDManp	5.124	4.140	4.047	3.661	3.978	3.784-3.873

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

1058.892 g/mol (C₃₉H₆₂R₂O₃₃, R = next and previous repeats, not counted in mol weight)