Secreted alkaline ribonucleases of micromycetes

Abstract

Many ribonucleases (RNases) have a selective cytotoxic effect on tumor cells. Of particular interest are enzymes that are phylogenetically distant from mammalian RNases, such as amphibian, fungal, and bacterial RNases, all insensitive to the action of the mammalian RNAse inhibitor. We screened 15 micromycete isolates for the presence of secreted alkaline ribonuclease. Seven isolates demonstrated the highest ribonucleolytic activity. Based on the phylogenetic analysis, the most active of them were identified as Fusarium sporotrichioides. The maximum level of activity (19000 units/mL) in the culture fluid of F. sporotrichioides was recorded on the third day of growth of the fungus. The obtained data on the thermal stability of the secreted F. sporotrichioides RNase, its molecular weight (11 kDa), and biosynthesis on a medium with a low phosphate content suggest that the enzyme belongs to the RNase T1/N1/U2 family. The culture fluid of F. sporotrichioides grown on the phosphate-deficient medium reduced the viability of A549 human lung adenocarcinoma cells by 16.3%; if the micromycete was grown on a medium with a high phosphate content, no toxicity of the culture fluid was detected. Thus, the secreted RNAse contributes to cytotoxicity. Further description and comprehensive study of the properties of the new RNase will help to establish the mechanisms of its cytotoxicity and identify the areas of application of the enzyme.

Keywords

• micromycetes
• fusarium
• ribonuclease
• thermostability
• cytotoxicity
• a549 lung adenocarcinoma cells