Keywords Parole chiave: Metal-Binding Protein, Ribonuclease Activity, Ribotoxins,
*** IBB - CNR *** Istituto di Biostrutture e Bioimmagini, C.N.R., Via Mezzocannone 16, I-80134 Napoli, Italy., Departamento de Bioquimica y Biologia Molecular, Facultad de Quimica, Universidad Complutense, E-28040 Madrid, Spain., Department of Environmental, Biological and Pharmaceutical Sciences and Technologies (DiSTABiF), University of Campania 'Luigi Vanvitelli', Via Vivaldi 43, I-81100 Caserta, Italy., Department of Environmental, Biological and Pharmaceutical Sciences and Technologies (DiSTABiF), University of Campania 'Luigi Vanvitelli', Via Vivaldi 43, I-81100 Caserta, Italy. Electronic address: firstname.lastname@example.org., Istituto di Biostrutture e Bioimmagini, C.N.R., Via Mezzocannone 16, I-80134 Napoli, Italy. Electronic address: email@example.com.,
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Ribotoxins are fungal proteins that serve as weapons against parasites and insects. They are strongly toxic due to their ability to enter host cells and inactivate ribosomes. Ageritin is the prototype of a new ribotoxin-like protein family present in basidiomycetes. We demonstrate that this enzyme has peculiar binding and enzymatic features. Different from other ribotoxins, its ribonucleolytic activity requires the presence of divalent cations, with a maximum activation in the presence of zinc ions, for which Ageritin exhibits the strongest affinity of binding. We modeled the catalytic metal binding site of Ageritin, made of the putative triad Asp68, Asp70 and His77. This report highlights that Ageritin has the structure and function of an RNase but a Mg(2+)/Zn(2+)-dependent mechanism of action, a new finding for ribotoxins. As a zinc-dependent toxin, Ageritin can be classified among the arsenal of zinc-binding proteins involved in fungal virulence.