Enhancement of copper content and specific activity of CotA laccase from Bacillus licheniformis by coexpression with CopZ copper chaperone in E. coli

Copper depletion of bacterial laccases obtained by heterologous expression in Escherichia coli is a common problem in production of these versatile biocatalysts. We demonstrate that coexpression of small soluble copper chaperones can mitigate this problem. The laccase CotA and the copper chaperone CopZ both from Bacillus licheniformis were used as model system. The use of the E. coli BL21(DE3) strain expressing CopZ and CotA simultaneously from two plasmids resulted in an 20% increase in copper occupancy and in 26% higher specific activity. We conclude that not only intracellular copper ion concentration, but also presence of an appropriate copper chaperone influences copper ion insertion into CotA laccase. Moreover, E. coli BL21(DE3) seems to lack such a copper chaperone which can be partially complemented by heterologous expression thereof. The presented system is simple and can routinely be used for improved heterologous production of bacterial laccase in E. coli.