Shedding light on YfhS and YjlC: novel effectors of the NADH dehydrogenase activity of the electron transport chain in Bacillus subtilis

Oxidative phosphorylation is the most efficient way of generating ATP in respiring cells. As high energy electrons are the major source of reactive oxygen species their production needs to be carefully calibrated. In most organisms, NADH dehydrogenase serves as the primary source and gateway of electrons. This complex is responsible for oxidizing NADH to NAD+, which liberates two electrons that are then fed into the respiratory chain. In the Gram-positive model bacterium, Bacillus subtilis, a transcription factor (Rex) is utilized to monitor the rise in NADH level and subsequently increase the production of the NADH dehydrogenase Ndh. Thus, the generation of electrons through this pathway is tightly regulated. In this report, we reveal the presence of another independent mechanism to moderate Ndh activity involving a previously uncharacterized protein, YfhS. Additionally, we present the first experimental evidence showing that the functional NADH dehydrogenase is a two-protein complex comprised of a membrane-associated YjlC and the enzyme Ndh. We find that absence of YfhS leads to cell morphology and growth defects that are corrected by spontaneous mutations in ndh. We note that increased production of NADH dehydrogenase complex proteins by itself is not detrimental. However, strikingly, it is lethal in a strain lacking yfhS. These results reveal that YfhS is an important moderator of NADH dehydrogenase activity. We also demonstrate that YfhS and YjlC are interaction partners. A model developed based on our data indicates that YfhS is an important regulator of intracellular NADH concentration. Compounds that target specific microbial (Type II) NADH dehydrogenase, which is absent in human mitochondria, are considered promising drug candidates to help address the threat posed by antibiotic-resistant bacteria. Overall, our data unveiling the importance of YfhS and YjlC in controlling Ndh activity could be harnessed for the development of new therapeutics.