CotA laccase, a novel aflatoxin oxidase from Bacillus licheniformis, transforms aflatoxin B1 to aflatoxin Q1 and epi-aflatoxin Q1.

In the present study, the CotA protein from Bacillus licheniformis ANSB821 was cloned and expressed in Escherichia coli. Apart from the laccase activities, we found that the recombinant CotA could effectively oxidize aflatoxin B₁ in the absence of redox mediators. The K_m, K_cat and V_max values of the recombinant CotA towards aflatoxin B₁ were 60.62 μM, 0.03 s^-1 and 10.08 μg min^-1 mg^-1, respectively. CotA-mediated aflatoxin B₁ degradation products were purified and identified to be aflatoxin Q₁ and epi-aflatoxin Q₁. The treatment of human liver cells L-02 with aflatoxin Q₁ and epi-aflatoxin Q₁ did not suppress cell viability and induce apoptosis. Molecular docking simulation revealed that hydrogen bonds and van der Waals interaction played an important role in aflatoxin B₁-CotA stability. These findings in the current study are promising for a possible application of CotA as a novel aflatoxin oxidase in degrading AFB₁ in food.