Fungal extracellular ribotoxins as insecticidal agents

Fungal ribotoxins were discovered almost 50 years ago as extracellular ribonucleases (RNases) with antitumoral properties. However, the biological function of these toxic proteins has remained elusive. The discovery of the ribotoxin HtA, produced by the invertebrates pathogen Hirsutella thompsonii, revived the old proposal that insecticidal activity would be their long searched function. Unfortunately, HtA is rather singular among all ribotoxins known in terms of sequence and structure similarities. Thus, it was intriguing to answer the question of whether HtA is just an exception or, on the contrary, the paradigmatic example of the ribotoxins function. The work presented uses HtA and α-sarcin, the most representative member of the ribotoxins family, to show their strong toxic action against insect larvae and cells.

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► The unique fungal ribotoxin Hirsutellin A is not the only insecticide protein of the family.
► α-Sarcin, the main member of the family, is comparable to HtA in toxicity against the larvae G. mellonella.
► In vivo and in vitro experiments show how ribotoxins are able to inactivate insect ribosomes.
►  Both toxins interact with vesicles made of insect membrane lipids, the first step for their toxicity.
► The insecticidal activity could be the biological function of ribotoxins produced by different fungi.