Eukaryotic Cell doi:10.1128/EC.00378-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Cryptococcus neoformans CAPSULAR AND EXOPOLYSACCHARIDE FRACTIONS MANIFEST PHYSICAL, CHEMICAL AND ANTIGENIC DIFFERENCES
Susana Frases,
Leonardo Nimrichter,
Nathan B. Viana,
Antonio Nakouzi,
and
Arturo Casadevall*
Department of Microbiology and Immunology, and Division of Infectious Diseases of the Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx, NY, 10461, USA; Laboratório de Estudos Integrados em Bioquímica Microbiana, Instituto de Microbiologia Professor Paulo de Góes, LPO-COPEA, Instituto de Ciências Biomédicas, and Instituto de Física, Universidade Federal do Rio de Janeiro, 21941-590, Brazil
* To whom correspondence should be addressed. Email:
casadeva{at}aecom.yu.edu.
 |
Abstract |
|---|
The human pathogenic fungus Cryptococcus neoformans has a large polysaccharide (PS) capsule and releases copious amounts of PS into cultures and infected tissues. The capsular PS is a major virulence factor that can elicit protective antibody responses. PS recovered from culture supernatants has historically provided an ample and convenient source of material for structural and immunological studies. Two major assumptions in such studies are that the structural features of the exopolysaccharide material faithfully mirror those of capsular PS and that the isolation methods do not change PS properties. However, a comparison of exopolysaccharide made by two isolation techniques with capsular PS stripped from cells with gamma radiation or DMSO revealed significant differences in glycosyl composition, mass, size, charge, viscosity, circular dichroism spectra and reactivity with monoclonal antibodies (mAbs). Our results strongly suggest that exopolysaccharides and capsular PS are structurally different. A noteworthy finding was that polysaccharide made by Cetyl trimethylammonium bromide (CTAB) precipitation had larger mass and different conformation, than PS isolated by concentration and filtration, suggesting that the most commonly used methodology to purify GXM alters the PS. Hence, the method used to isolate PS can significantly influence the structural and antigenic properties of the product. Our findings have important implications for current views of the relationship between capsular and exopolysaccharides, for the generation of PS preparations suitable for immunological studies and for the formulation of PS-based vaccines for the prevention of cryptococcosis.
