Structural and functional properties of the Trichosporon asahii glucuronoxylomannan

The virulence attributes of Trichosporon asahii are virtually unknown, despite its growing relevance as causative agent of superficial and invasive diseases in humans. Glucuronoxylomannan (GXM) is a well described virulence factor of pathogenic species in the Cryptococcus genus. GXM is also produced by species of the Trichosporon genus, and both polysaccharides share antigenic determinants, but unlike cryptococcal GXM, relatively little work has been done on trichosporal GXMs. In this study, we analyzed structural and functional aspects of GXM produced by T. asahii and compared them to the properties of the cryptococcal polysaccharide. Trichosporal and cryptococcal GXM shared antigenic reactivity, but the former polysaccharide had smaller effective diameter and negative charge. GXM anchoring to the cell wall was perturbed by dimethylsulfoxide and required interactions of chitin-derived oligomers with the polysaccharide. GXM from T. asahii supernatants are incorporated by acapsular mutants of Cryptococcus neoformans, which renders these cells more resistant to phagocytosis by mouse macrophages. In summary, our results establish that despite similarities in cell wall anchoring, antigenic and antiphagocytic properties, trichosporal and cryptococcal GXMs manifest major structural differences that may directly affect polysaccharide assembly at the fungal surface.