The Ribosome-Binding Mode of Trichothecene Mycotoxins Rationalizes Their Structure-Activity Relationships

Abstract

Trichothecenes are the most prevalent mycotoxins contaminating cereal grains. Some of them are also considered as the virulence factors of Fusarium head blight disease. However, the mechanism behind the structure-activity relationship for trichothecenes remains unexplained. Filling this information gap is a crucial step for developing strategies to manage this large family of mycotoxins in food and feed. Here, we perform an in-depth re-examination of the existing structures of Saccharomyces cerevisiae ribosome complexed with three different trichothecenes. Multiple binding interactions between trichothecenes and 25S rRNA, including hydrogen bonds, nonpolar pi stacking interactions and metal ion coordination interactions, are identified as important binding determinants. These interactions are mainly contributed by the key structural elements to the toxicity of trichothecenes, including the oxygen in the 12,13-epoxide ring and a double bond between C⁹ and C¹⁰. In addition, the C³-OH group also participates in binding. The comparison of three trichothecenes binding to the ribosome, along with their binding pocket architecture, suggests that the substitutions at different positions impact trichothecenes binding in two different patterns. Moreover, the binding of trichothecenes induced conformation changes of several nucleotide bases in 25S rRNA. This then provides a structural framework for understanding the structure-activity relationships apparent in trichothecenes. This study will facilitate the development of strategies aimed at detoxifying mycotoxins in food and feed and at improving the resistance of cereal crops to Fusarium fungal diseases.

Keywords: binding contacts; binding mode; binding pocket architecture; mechanism of structure–activity relationships; mycotoxins; ribosome RNA; trichothecene.

Figure 1

The two-dimensional and three-dimensional structures of deoxynivalenol (DON), T-2 toxin, and verrucarin A and their position numbering. The three-dimensional structures were visualized using PyMOL 2.3.4. The PDB accession number of DON is 3J6, those of T-2 toxin and verrucarin A are 3 L2 and ZBA, respectively.

Figure 2

The binding of trichothecene mycotoxins of DON, T-2 toxin and verrucarin A to yeast 80 S ribosome. (A,B): The binding contacts of DON to 25S rRNA; (C,D): The binding contacts of T-2 toxin to 25S rRNA; (E,F): The binding contacts of verrucarin A to 25S rRNA. The hydrophobic stacking interaction between two rings was shaded in light green, and the additional contacts relative to DON were labeled in the red dash lines.

Figure 3

The binding pocket formed merely by 25S rRNA for DON, T-2 toxin and verrucarin A. (A) The partial secondary structure of Saccharomyces cerevisiae 25S rRNA adopted from the previous report [41], the nucleotides contributing to binding pocket formation were circled in red; (B) DON anchoring in the binding pocket; (C) T-2 toxin anchoring in the binding pocket; (D) verrucarin A anchoring in the binding pocket.

Figure 4

The conformation changes of several nucleobases around the binding pocket in 25S rRNA upon trichothecenes binding. The vacant 25S rRNA was taken as the reference and shown in gray, the 25S rRNA bound with DON was in light blue, the 25S rRNA bound with T-2 toxin was in yellow, and that bound with verrucarin A was in deep blue.

Figure 5

The effect of C³-OH conformation change in DON on the interactions to the ribosome. The C³-OH in 3-epi-DON was colored in yellow and red. The dotted lines indicate the binding interactions.