Schematic depicting the targeting strategy to localize mtON to the mitochondrial inner membrane (IM). The electron transport chain (ETC) complexes generate the endogenous mitochondrial PMF by proton pumping, represented by the + and - across the IM. Mitochondrial ATP synthase utilizes the PMF to convert ADP to ATP. The N-terminal mitochondria target sequence from the IMMT1 protein shown in red; GFP shown in green. In response to light, mtON pumps protons from the mitochondrial matrix to the intermembrane space (IMS). 