Among the putative defense proteins that occur in fungi, one of the best studied is α-sarcin, produced by the mold Aspergillus giganteus. This protein is the most significant member of the ribotoxin family, which consists of extracellular rRNA ribonucleases that display cytotoxic activity toward animal cells. Ribotoxins are rRNA endonucleases that catalyze the hydrolysis of the phosphodiester bond between G4325 and A4326 from the rat 28S rRNA. The results of several experimental approaches have led to propose ribotoxins as insecticidal agents. In this work, we report that α-sarcin displays a strong antifungal activity against Penicillium digitatum, being able to enter into the cytosol where it inactivates the ribosomes, thus killing the cells and arresting the growth of the fungus. This is the first time that a ribotoxin has been found to display antifungal activity. Therefore, this protein could play, besides the already proposed insecticidal function, a role in nature as an antifungal agent.
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