Theoretical insights into the mechanism underlying aflatoxin B1 transformation by the BsCotA-methyl syringate system.

Global concern exists regarding the contamination of food and animal feed with aflatoxin B 1 (AFB 1), which poses a threat to the health of both humans and animals. Previously, we found that a laccase from Bacillus subtilis (Bs CotA) effectively detoxified AFB 1 in a reaction mediated by methyl syringate (MS), although the underlying mechanism has not been determined. Therefore, our primary objective of this study was to explore the detoxification mechanism employed by Bs CotA. First, the enzyme and mediator dependence of AFB 1 transformation were studied using the Bs CotA-MS system, which revealed the importance of MS radical formation during the oxidation process. Aflatoxin Q 1 (AFQ 1) resulting from the direct oxidation of AFB 1 by Bs CotA, was identified using ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results of UPLC-MS/MS and density functional theory calculations indicated that the products included AFQ 1 , AFB 1 -, and AFD 1 -MS-coupled products in the Bs CotA-MS system. The toxicity evaluations revealed that the substances derived from the transformation of AFB 1 through the Bs CotA-MS mechanism exhibited markedly reduced toxicity compared to AFB 1. Finally, we proposed a set of different AFB 1 -transformation pathways generated by the Bs CotA-MS system based on the identified products. These findings greatly enhance the understanding of the AFB 1 -transformation mechanism of the laccase-mediator system. [Display omitted] • AFB 1 can be transformed by Bs CotA both in the presence or absence of a mediator. • AFB 1 was directly converted to AFQ 1 by Bs CotA. • Coupling reactions occurred between AFB 1 and MS radical. • The identified products exhibit lower toxicity levels than AFB 1. [ABSTRACT FROM AUTHOR]