In recent decades, fungus laccases (p-diphenol-dioxygen oxidoreductases; EC 1.10.3.2) have attracted the attention of researches due to their wide range of biotechnological and industrial applications. In the present study, we have cloned a gene encoding laccase (poxa1b) from Pleurotus ostreatus and then heterologously expressed in Escherichia coli BL21. The biochemical properties of POXA1b were characterized using ABTS as a typical substrate of laccases. Moreover, the in vitro oxidation of the benzo[a]pyrene was investigated in the presence or absence of ABTS. The codon-optimized poxa1b showed higher expression yields and efficiency in comparison with the wild-type (p < 0.01). The maximum activity of POXA1b (2075 UL-1) was observed after incubation at 50 °C for 0.5 h and the enzyme retained more than 85% of its initial activity after 2 h incubation at 25–45 °C. The optimum pH of the enzyme was pH4 and the enzyme was stable when being incubated at pH range from 2.5 to 4.5 for 2 h in the absence of ABTS, the enzyme oxidized a little amount of benzo[a]pyrene, whereas its oxidation enhanced following the ABTS addition. These findings indicate POXA1b of P. ostreatus as a promising candidate for further biotechnological approaches.

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