Enhancement of hydrogen peroxide stability of a novel Anabaena sp. DyP-type peroxidase by site-directed mutagenesis of methionine residues

摘要

Previous reports have shown that a unique bacterial dye-decolorizing peroxidase from the cyanobacterium Anabaena sp. strain PCC7120 (AnaPX) efficiently oxidizes both recalcitrant anthraquinone dyes (AQ) and typical aromatic peroxidase substrates. In this study, site-directed mutagenesis to replace five Met residues in AnaPX with high redox residues Ile, Leu, or Phe was performed for the improvement of the enzyme stability toward H₂O₂. The heme cavity mutants M401L, M401I, M401F, and M451I had significantly increased H₂O₂ stabilities of 2.4-, 3.7-, 8.2-, and 5.2-fold, respectively. Surprisingly, the M401F and M451I retained 16% and 5% activity at 100 mM H₂O₂, respectively, in addition to maintaining high dye-decolorization activity toward AQ and azo dyes at 5 mM H₂O₂ and showing a slower rate of heme degradation than the wildtype enzyme. The observed stabilization of AnaPX may be attributed to the replacement of potentially oxidizable Met residues either increasing the local stability of the heme pocket or limiting of the self-inactivation electron transfer pathways due to the above mutations. The increased stability of AnaPX variants coupled with the broad substrate specificity can be potentially useful for the further practical application of these enzymes especially in bioremediation of wastewater contaminated with recalcitrant AQ.