An ectophosphatase activity inCryptococcus neoformans

Abstract

There is increasing evidence in the literature showing that fungal pathogens express biologically active ectoenzymes. The expression of surface phosphatases at the cell surface of Cryptococcus neoformans, the etiologic agent of cryptococcosis, was evaluated in the present study. Different isolates of C. neoformans express ectophosphatase activity, which is not influenced by capsule size or serotype. The cryptococcal enzyme is an acid phosphatase, inhibited by classic inhibitors of ectophosphatases, including ammonium molybdate and sodium salts of fluoride and orthovanadate. Only the inhibition of enzyme activity caused by sodium orthovanadate has been shown to be irreversible. The cryptococcal ectoenzyme is also inhibited by Zn2+ and inorganic phosphate, the final product of reactions catalyzed by phosphatases. The ectophosphatase from C. neoformans efficiently releases phosphate groups from different phosphorylated amino acids, giving a higher rate of phosphate removal when phosphothreonine is used as a substrate. Yeast cells with irreversibly inhibited ectophosphatases are less capable of adhering to animal epithelial cells than fungi fully expressing enzyme activity, suggesting that ectoenzyme expression can contribute to the pathogenesis of C. neoformans.