STRUCTURE OF THE O-DEACETYLATED GLUCURONOXYLOMANNAN FROM CRYPTOCOCCUS-NEOFORMANS SEROTYPE-C AS DETERMINED BY 2D H-1-NMR SPECTROSCOPY

The primary structure of the O-deacetylated capsular glucuronoxylomann an (GXM) isolated from Cryptococcus neoformans serotype C was investig ated by 2D NMR spectroscopy. Assignment of the H-1 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 40 1). These isolates contain the same polysaccharide glycosyl residues b ut in different proportions. The serotype C GXM consists of two repeat ing polysaccharide units that have the following structures: [GRAPHICS ] It is not known if these repeating units comprise a single or two se parate polymer chains. The relative amounts of the more highly branche d 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 t o explain the serological specificity of these isolates with C. neofor mans factor sera, as was previously determined by ELISA in this labora tory. The octasaccharide 1 component is the one previously postulated as the structure of the serotype C GXM although definitive placement o f the beta-Xyl-(1-->4) residues had previously not been determined. Th e 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 u nit usually attributed to serotype A GXM.