I am designing an experiment to measure the effect of a mutant electron transfer (ET) mediating protein on the production of ROS. The ET mediator is located in the periplasm, and I am expressing it in E. coli.
If you will extract the recombinant protein from your E. coli and use it in an in-vitro-assay, then you would not need to target it. For an in-vivo-assay, you can achieve endogenous targeting expressing the transgene including regulatory elements of ET.