Chemical structure of -galactofuranose-containing polysaccharide and O-linked oligosaccharides obtained from the cell wall of pathogenic dematiaceous fungus Fonsecaea pedrosoi

Abstract

Fonsecaea pedrosoi is the main etiologic agent of chromoblastomycosis, usually occurring in tropical and subtropical areas. The cell wall components of pathogenic microorganisms behave as an antigen and/or ligand of the innate immune response. The cells of F. pedrosoi reacted with the α-galactopyranose-binding lectin (Griffonia simplicifolia lectin 1B4 isolectin, GSL 1B4), as well as the α-mannose-binding lectin, concanavalin A. The cell wall glycoprotein was isolated from conidial cells of F. pedrosoi, and its structure was analyzed by (1)H-nuclear magnetic resonance (NMR) and (13)C-NMR experiments. The N-linked polysaccharide moiety consists of a backbone β-1,6-linked galactofuranose and α-1,6-linked mannose polymers, both of which are substituted with α-1,2-linked glucose side-chains. Furthermore, the glycoprotein contained a large amount of O-linked oligosaccharides, especially a hexaose that constituted approximately 20% of the glycoprotein. Unexpectedly, the hexaose had a highly branched structure which consisted of galactofuranose, galactopyranose, glucose and mannose residues as follows: An anti-F. pedrosoi antibody specifically reacted with the cells of F. pedrosoi, whereas other fungal cells that contain galactofuranose residues did not react. The reactivity of the antibody was strongly inhibited by the branched hexaose, suggesting that the characteristic structure of the O-linked hexaose involves the antigenic specificity of the cells.