Localization of the death effector domain of Fas-associated death domain protein into the membrane of Escherichia coli induces reactive oxygen species-involved cell death.

The death effector domain (DED) of the mammalian apoptosis mediator, Fas-associated death domain protein (FADD), induces Escherichia coli cell death under aerobic culture conditions, yet the mechanisms by which FADD-DED induces cell death are not fully understood. Oxidative stress has been implicated as one of the mechanisms. Using a proteomic approach and validation by coexpression analysis, we illustrate that overexpression of FADD-DED in E. coli invokes protein expression changes that facilitate conversion of pro-oxidant NADH into antioxidant NADPH. Typically, isocitrate dehydrogenase, phosphoenolpyruvate carboxykinase, and pyruvate kinase are downregulated and malate dehydrogenase is upregulated. We reasoned that such a change in E. coli cells is an active response to reduce the size of the NADH pool, thereby decreasing the level of ROS generation. From the coexpression studies, we observed that DNA binding protein Hns, which induces growth arrest when overexpressed heterologously, alleviated the cell killing effect of FADD-DED. FADD-DED was expressed as a noncovalently linked multimeric protein in the membrane of E. coli. Exogenous treatment of E. coli cells with FADD-DED in the presence of a membrane component induced cell death, which was accompanied by a shift of the redox balance and a decrease in the cellular ATP level. Cell death was blocked by prior expression of thioredoxin. Localization of FADD-DED to the membrane may shift the cells into a state that stimulates and fuels ROS generation. The cell death mechanism mediated by ROS may mimic antibiotic-mediated bacterial cell death or Bax-mediated apoptosis in mammalian cells. Our results provide a common mechanistic feature of ROS-involved cell death throughout prokaryotes and eukaryotes.