Purification, characterization and cytotoxicity assessment of Ageritin: The first ribotoxin from the Basidiomycete mushroom Agrocybe aegerita

Publication date: Available online 20 February 2017
Source:Biochimica et Biophysica Acta (BBA) - General Subjects
Author(s): Nicola Landi, Severina Pacifico, Sara Ragucci, Rosario Iglesias, Simona Picolella, Adolfo Amici, Antonella M.A. Di Giuseppe, Antimo Di Maro
BackgroundSeveral species belonging to Ascomycota phylum produce extracellular ribonucleases, known as ribotoxins, which exhibit RNase activity through the cleavage of a single phosphodiester bond, located at the universally conserved sarcin/ricin loop of the large rRNA leading inhibition of protein biosynthesis. Clarifying the structure-function relationship in ribotoxins is interesting for their use in human tumour therapy and in construction of pests resistant transgenic plants.ResultsThe ribotoxin Ageritin has been isolated for the first time from Basidiomycetes class. The enzyme, characterized by means of its amino acid composition, N-terminal sequence and a circular dichroism, structurally differs from Ascomycota ribotoxin prototype, although it was able, as α-sarcin, to release a specific α-fragment. However, it does not display aspecific ribonucleolytic activity. Ageritin exerts cytotoxicity and cell death promoting effects towards CNS model cell lines (SK-N-BE(2)-C, U-251 and C6), as vinblastine, a plant alkaloid used in cancer therapy. Moreover, our results indicate that Ageritin initially activates caspase-8, whereas caspase-9 cleavage was not detected, demonstrating the involvement of extrinsic apoptotic pathway.ConclusionsOur findings show that Ageritin is the earliest diverging member of the Ascomycota ribotoxin family, suggesting that ribotoxins are more widely distributed among fungi than previously believed.General significanceAgeritin, structurally different from the widely known Ascomycota ribotoxins, with promising anti-cancer properties vs. aggressive brain tumours, has been found from the basidiomycete fungus Agrocybe aegerita. Finally, this finding highlights that ribotoxin family has divergent members in Basidiomycota phylum, whose structural and functional characterization can give new information on ribotoxin or ribonuclease superfamilies.

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