The enzymatic detoxification of the mycotoxin deoxynivalenol: identification of DepA from the DON epimerization pathway

Abstract

The biological detoxification of mycotoxins, including deoxynivalenol (DON), represents a very promising approach to address the challenging problem of cereal grain contamination. The recent discovery of Devosia mutans 17-2-E-8 (Devosia spp. 17-2-E-8), a bacterial isolate capable of transforming DON to the non-toxic stereoisomer 3-epi-deoxynivalenol, along with earlier reports of bacterial species capable of oxidizing DON to 3-keto-DON, has generated interest in the possible mechanism and enzyme(s) involved. An understanding of these details could pave the way for novel strategies to manage this widely present toxin. It was previously shown that DON epimerization proceeds through a two-step biocatalysis. Significantly, this report describes the identification of the first enzymatic step in this pathway. The enzyme, a dehydrogenase responsible for the selective oxidation of DON at the C3 position, was shown to readily convert DON to 3-keto-DON, a less toxic intermediate in the DON epimerization pathway. Furthermore, this study provides insights into the PQQ dependence of the enzyme. This enzyme may be part of a feasible strategy for DON mitigation within the near future.

Figure 1

Devosia mutans 17‐2‐E‐8 transforms DON into 3‐keto‐DON.

Figure 2

Effects of Ca²⁺ and PQQ on partially purified DepA from Devosia mutans 17‐2‐E‐8. Reactions contained 50 μg ml⁻¹ DON in Tris, pH 7.5, with 1 mM Ca²⁺ and 100 μM PQQ. Buffers and water used to dilute substrates have been treated with Chelex 100 (Sigma) to remove any metal ion. This experiment was replicated with independently purified protein with similar results.

Figure 3

DON transformation ability of heterologously expressed DepA. A. PQQ is essential for DepA activity. Reactions contained 100 μg ml⁻¹ DON, in Tris pH 7.5 with 15 μg of purified DepA in the presence or absence of 100 μM PQQ. B. DepA completely transforms DON to 3‐keto‐DON. Each reaction consisted of 100 μg ml⁻¹ DON, 40 μM phenazine and 100 μM PQQ with or without 5 μg of DepA. Reactions were incubated overnight at room temperature and replicated with an independent purification.