title: Type-specific polysaccharides of Cryptococcus neoformans. n.m.r.-spectral study of a glucuronomannan chemically derived from a Tremella mesenterica exopolysaccharide.
abstract: A glucuronomannan (GM) was derived by removal, through Smith degradation, of xylose from the native (3-O-acetylglucurono)xylomannan exopolysaccharide isolated from Tremella mesenterica. 13C-N.m.r. chemical shifts measured at various pD values were compared for p-nitrophenyl beta-D-glucopyranosiduronic acid (1) and two GMs (2 and 3) differing in GlcA content (Man:GlcA; 2, 10:1; and 3, 5:1). Also measured and compared were pKa values for 1 and 2. One-dimensional and two-dimensional (COSY and HETCOR) n.m.r. data allowed unambiguous assignments of pD-sensitive chemical shifts due to 2-O-beta-D-GlcpA substituents attached to a (1----3)-linked alpha-D-Manp backbone. The pKa and n.m.r. data indicated that the CO2H groups in either GM are independent of each other, and are similar in behavior to those of p-nitrophenyl beta-D-glucopyranosiduronic acid molecules. The n.m.r. data confirmed the previous, chemically deduced, structural role of GlcpA in the native polysaccharide from T. mesenterica, and indicated that significant pD-induced changes occur in the stabilities of the glycosidic orientations in the GM. Previous 13C-n.m.r. assignments for 2-O-beta-D-GlcpA in polysaccharides derived from Cryptococcus neoformans serotype A-variant were confirmed, except for the signal due to the anomeric carbon atom. This signal is now known to be pD-sensitive. In acidic solutions, it is coincident with the signal (104.5 p.p.m.) due to the anomeric carbon atoms of the unsubstituted alpha-D-Manp backbone residues. In basic solutions, the 2-O-beta-D-GlcpA anomeric carbon resonance is shifted upfield by approximately 0.2 p.p.m., and is observed as a separate signal.
authors.affiliation: Department of Chemistry, Georgia State University, Atlanta 30303.
authors.forename: R
authors.initials: R
authors.lastname: Cherniak
authors.forename: R G
authors.initials: RG
authors.lastname: Jones
authors.forename: M E
authors.initials: ME
authors.lastname: Slodki
mesh_terms: D001487:Basidiomycota / Q000032:analysis*; D055598:Chemical Phenomena; D002621:Chemistry; D003454:Cryptococcus / Q000032:analysis*; D003455:Cryptococcus neoformans / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D011134:Polysaccharides; D011135:Polysaccharides, Bacterial / Q000032:analysis*; D013010:Sonication
chemical_list: D011134:Polysaccharides; D011135:Polysaccharides, Bacterial; C027478:glucuronoxylomannan