文獻名： Cryptococcus neoformans Capsular Polysaccharide and Exopolysaccharide Fractions Manifest Physical, Chemical, and Antigenic Differences
作者： Susana Frases1, Leonardo Nimrichter2, Nathan B. Viana3,4, Antonio Nakouzi1 and Arturo Casadevall1,5
1Department of Microbiology and Immunology
5Division of Infectious Diseases of the Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461
2Laboratório de Estudos Integrados em Bioquímica Microbiana, Instituto de Microbiologia Paulo de Góes
3LPO-COPEA, Instituto de Ciências Biomédicas
4Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-590, Brazil
摘要：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 dimethyl sulfoxide revealed significant differences in glycosyl composition, mass, size, charge, viscosity, circular-dichroism spectra, and reactivity with monoclonal antibodies. Our results strongly suggest that exopolysaccharides and capsular PS are structurally different. A noteworthy finding was that PS made by cetyltrimethylammonium bromide precipitation had a larger mass and a different conformation than PS isolated by concentration and filtration, suggesting that the method most commonly used to purify glucuronoxylomannan 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 PS 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.
