Heterologous Production and Functional Characterization of Ageritin, a Novel Type of Ribotoxin Highly Expressed during Fruiting of the Edible Mushroom Agrocybe aegerita

Fungi produce various defense proteins against antagonists, including ribotoxins. These toxins cleave a single phosphodiester bond within the universally conserved sarcin-ricin loop of ribosomes and inhibit protein biosynthesis. Here, we report on the structure and function of ageritin, a previously reported ribotoxin from the edible mushroom; Agrocybe aegerita; The amino acid sequence of ageritin was derived from cDNA isolated from the dikaryon; A. aegerita; AAE-3 and lacks, according to; in silico; prediction, a signal peptide for classical secretion, predicting a cytoplasmic localization of the protein. The calculated molecular weight of the protein is slightly higher than the one reported for native ageritin. The; A. aegerita; ageritin-encoding gene,; AaeAGT1; , is highly induced during fruiting, and toxicity assays with; AaeAGT1; heterologously expressed in; Escherichia coli; showed a strong toxicity against; Aedes aegypti; larvae yet not against nematodes. The activity of recombinant; A. aegerita; ageritin toward rabbit ribosomes was confirmed; in vitro; Mutagenesis studies revealed a correlation between; in vivo; and; in vitro; activities, indicating that entomotoxicity is mediated by ribonucleolytic cleavage. The strong larvicidal activity of ageritin makes this protein a promising candidate for novel biopesticide development.; IMPORTANCE; Our results suggest a pronounced organismal specificity of a protein toxin with a very conserved intracellular molecular target. The molecular details of the toxin-target interaction will provide important insight into the mechanism of action of protein toxins and the ribosome. This insight might be exploited to develop novel bioinsecticides.