Reconstitution of Active Mycobacterial Binuclear Iron Monooxygenase Complex in Escherichia coli

Abstract

ABSTRACTBacterial binuclear iron monooxygenases play numerous physiological roles in oxidative metabolism. Monooxygenases of this type found in actinomycetes also catalyze various useful reactions and have attracted much attention as oxidation biocatalysts. However, difficulties in expressing these multicomponent monooxygenases in heterologous hosts, particularly inEscherichia coli, have hampered the development of engineered oxidation biocatalysts. Here, we describe a strategy to functionally express the mycobacterial binuclear iron monooxygenase MimABCD inEscherichia coli. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of themimABCDgene expression inE. colirevealed that the oxygenase components MimA and MimC were insoluble. Furthermore, although the reductase MimB was expressed at a low level in the soluble fraction ofE. colicells, a band corresponding to the coupling protein MimD was not evident. This situation rendered the transformedE. colicells inactive. We found that the following factors are important for functional expression of MimABCD inE. coli: coexpression of the specific chaperonin MimG, which caused MimA and MimC to be soluble inE. colicells, and the optimization of themimDnucleotide sequence, which led to efficient expression of this gene product. These two remedies enabled this multicomponent monooxygenase to be actively expressed inE. coli. The strategy described here should be generally applicable to theE. coliexpression of other actinomycetous binuclear iron monooxygenases and related enzymes and will accelerate the development of engineered oxidation biocatalysts for industrial processes.