The ribotoxin-like protein Ostreatin from Pleurotus ostreatus fruiting bodies: Confirmation of a novel ribonuclease family expressed in basidiomycetes

• Published in: International journal of biological macromolecules Vol. 161; pp. 1329 - 1336
• Main Authors: Landi, Nicola, Ragucci, Sara, Russo, Rosita, Valletta, Mariangela, Pizzo, Elio, Ferreras, J. Miguel, Di Maro, Antimo
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-10-2020
• Subjects: Agaricales; Ageritin; Amino Acid Sequence; Ascomycota - genetics; Base Sequence; Chromatography, Gel; Enzyme Activation; Fruiting Bodies, Fungal - enzymology; Gene Expression; Models, Molecular; Mycotoxins - chemistry; Mycotoxins - genetics; Mycotoxins - isolation & purification; Mycotoxins - metabolism; Pleurotus - enzymology; Pleurotus ostreatus; Protein Conformation; Recombinant Proteins; Ribonucleases - chemistry; Ribonucleases - genetics; Ribonucleases - isolation & purification; Ribonucleases - metabolism; Ribotoxin-like proteins; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Structure-Activity Relationship; Ageritin; Ribotoxin-like proteins; Pleurotus ostreatus
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2020.07.267

Fungi produce several toxins active against plants, animal or humans. Among them, ribotoxins are enzymes that specifically attack ribosomes irreparably compromising protein synthesis, useful as insecticides or as anticancer agents. Here, a novel ribotoxin from the edible mushroom Pleurotus ostreatus has been purified and characterized. This ribotoxin, named Ostreatin, is a specific ribonuclease releasing α-fragment when incubated with yeast or rabbit ribosomes. Ostreatin shows IC50 of 234 pM in rabbit reticulocyte lysate, and metal dependent endonuclease activity. Following the completion of Ostreatin primary structure, we ascertained that this toxin is homologous to Ageritin, the first ribotoxin-like protein from the basidiomycete Agrocybe aegerita, with which it shares 38.8% amino acid sequence identity. Ostreatin consists of 131 amino acid residues with an experimental molecular mass of 14,263.51 Da ([M+H+]+). Homology modeling revealed that Ostreatin and Ageritin share a similar fold in which the common catalytic triad is conserved. Purified Ostreatin lacks N-terminal and C-terminal peptides, which instead are present in the Ostreatin coding sequence. Such peptides are probably involved in protein sorting and for this they could be removed.
Our findings confirm the presence of ribotoxin-like proteins in basidiomycetes edible mushrooms, that we propose as novel tool for biotechnological applications.
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•Ostreatin from edible mushroom Pleurotus ostreatus releases the α-fragment.•Primary structure was achieved by bioinformatic approach and mass spectrometry.•Homology modeling displays a similar fold with the prototype Ageritin.•Ostreatin is the second member of basidiomycetes ribotoxin-like proteins family.