title: Distribution of the O-acetyl groups and β-galactofuranose units in galactoxylomannans of the opportunistic fungus Cryptococcus neoformans.
abstract: Galactoxylomannans (GalXMs) are a mixture of neutral and acidic capsular polysaccharides produced by the opportunistic fungus Cryptococcus neoformans that exhibit potent suppressive effects on the host immune system. Previous studies describing the chemical structure of C. neoformans GalXMs have reported species without O-acetyl substituents. Herein we describe that C. neoformans grown in capsule-inducing medium produces highly O-acetylated GalXMs. The location of the O-acetyl groups was determined by nuclear magnetic resonance (NMR) spectroscopy. In the neutral GalXM (NGalXM), 80% of 3-linked mannose (α-Manp) residues present in side chains are acetylated at the O-2 position. In the acidic GalXM also termed glucuronoxylomannogalactan (GXMGal), 85% of the 3-linked α-Manp residues are acetylated either in the O-2 (75%) or in the O-6 (25%) position, but O-acetyl groups are not present at both positions simultaneously. In addition, NMR spectroscopy and methylation analysis showed that β-galactofuranose (β-Galf) units are linked to O-2 and O-3 positions of nonbranched α-galactopyranose (α-Galp) units present in the GalXMs backbone chain. These findings highlight new structural features of C. neoformans GalXMs. Among these features, the high degree of O-acetylation is of particular interest, since O-acetyl group-containing polysaccharides are known to possess a range of immunobiological activities.
authors.affiliation: Laboratório de Glicobiologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21941902Rio de Janeiro, Brazil.
authors.forename: Jose O
authors.initials: JO
authors.lastname: Previato
authors.affiliation: National Research Council, 100 Sussex Dr, K1A 0R6Ottawa, Canada.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Vinogradov
authors.affiliation: Université Lille, CNRS, UMR 8576, UGSF, Unité de Glycobiologie Structurale et Fonctionnelle,F 59000Lille, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Maes
authors.affiliation: Laboratório de Glicobiologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21941902Rio de Janeiro, Brazil.
authors.forename: Leonardo M
authors.initials: LM
authors.lastname: Fonseca
authors.affiliation: Université Lille, CNRS, UMR 8576, UGSF, Unité de Glycobiologie Structurale et Fonctionnelle,F 59000Lille, France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Guerardel
authors.affiliation: Laboratório de Glicobiologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21941902Rio de Janeiro, Brazil.
authors.forename: Priscila A V
authors.initials: PAV
authors.lastname: Oliveira
authors.affiliation: Laboratório de Glicobiologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21941902Rio de Janeiro, Brazil.
authors.forename: Lucia
authors.initials: L
authors.lastname: Mendonça-Previato
mesh_terms: D003455:Cryptococcus neoformans / Q000737:chemistry*; D062610:Fungal Polysaccharides / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry*
chemical_list: D062610:Fungal Polysaccharides; D011134:Polysaccharides; C043689:galactoxylomannan
keywords: Cryptococcus; O-acetyl; capsular polysaccharides; galactofuranose; galactoxylomannans