Improvement of aflatoxin B degradation ability by CotA-laccase Q441A mutant.

Aflatoxin B (AFB) contamination seriously threatens nutritional safety and common health. Bacterial CotA-laccases have great potential to degrade AFB without redox mediators. However, CotA-laccases are limited because of the low catalytic activity as the spore-bound nature. The AFB degradation ability of CotA-laccase from ANSB821 has been reported by a previous study in our laboratory. In this study, a Q441A mutant was constructed to enhance the activity of CotA-laccase to degrade AFB. After the site-directed mutation, the mutant Q441A showed a 1.73-fold higher catalytic efficiency (/K) towards AFB than the wild-type CotA-laccase did. The degradation rate of AFB by Q441A mutant was higher than that by wild-type CotA-laccase in the pH range from 5.0 to 9.0. In addition, the thermostability was improved after mutation. Based on the structure analysis of CotA-laccase, the higher catalytic efficiency of Q441A for AFB may be due to the smaller steric hindrance of Ala441 than Gln441. This is the first research to enhance the degradation efficiency of AFB by CotA-laccase with site-directed mutagenesis. In summary, the mutant Q441A will be a suitable candidate for highly effective detoxification of AFB in the future.