title: Self-aggregation of Cryptococcus neoformans capsular glucuronoxylomannan is dependent on divalent cations.
abstract: The capsular components of the human pathogen Cryptococcus neoformans are transported to the extracellular space and then used for capsule enlargement by distal growth. It is not clear, however, how the glucuronoxylomannan (GXM) fibers are incorporated into the capsule. In the present study, we show that concentration of C. neoformans culture supernatants by ultrafiltration results in the formation of highly viscous films containing pure polysaccharide, providing a novel, nondenaturing, and extremely rapid method to isolate extracellular GXM. The weight-averaged molecular mass of GXM in the film, determined using multiangle laser light scattering, was ninefold smaller than that of GXM purified from culture supernatants by differential precipitation with cetyl trimethyl ammonium bromide (CTAB). Polysaccharides obtained either by ultrafiltration or by CTAB-mediated precipitation showed different reactivities with GXM-specific monoclonal antibodies. Viscosity analysis associated with inductively coupled plasma mass spectrometry and measurements of zeta potential in the presence of different ions implied that polysaccharide aggregation was a consequence of the interaction between the carboxyl groups of glucuronic acid and divalent cations. Consistent with this observation, capsule enlargement in living C. neoformans cells was influenced by Ca(2+) in the culture medium. These results suggest that capsular assembly in C. neoformans results from divalent cation-mediated self-aggregation of extracellularly accumulated GXM molecules.
authors.affiliation: Laboratório de Estudos Integrados em Bioquímica Microbiana, Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, 21941-590, Brazil.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Nimrichter
authors.forename: Susana
authors.initials: S
authors.lastname: Frases
authors.forename: Leonardo P
authors.initials: LP
authors.lastname: Cinelli
authors.forename: Nathan B
authors.initials: NB
authors.lastname: Viana
authors.forename: Antonio
authors.initials: A
authors.lastname: Nakouzi
authors.forename: Luiz R
authors.initials: LR
authors.lastname: Travassos
authors.forename: Arturo
authors.initials: A
authors.lastname: Casadevall
authors.forename: Marcio L
authors.initials: ML
authors.lastname: Rodrigues
mesh_terms: D016667:Bacterial Capsules / Q000737:chemistry*; D002413:Cations, Divalent / Q000737:chemistry*; D003455:Cryptococcus neoformans / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry*
chemical_list: D002413:Cations, Divalent; D011134:Polysaccharides; C027478:glucuronoxylomannan