Dynamic NADPH homeostasis is essential to obtain maximal antioxidant protection in Escherichia coli

M. V. HUMBERT; CARRILLO, N.; ADRIANA DEL ROSARIO KRAPP

San Miguel de Tucuman, Argentina

Congreso; XLIV Reunión anual de SAIB; 2009

SAIB

Bacteria have evolved sophisticated molecular mechanisms to monitor oxidant levels and to activate antioxidant defense genes in response to specific signals. SoxR serves in Escherichia coli as a redox sensing protein activated upon exposure to superoxide- generating agents such as methyl viologen (MV), and becomes active when the 2Fe-2S cluster is oxidized. During aerobic growth, SoxR is maintained in the inactive reduced form by a reducing activity dependent on NADPH. When oxidized, SoxR activates the transcription of the soxS gene. The SoxS protein induces transcription of the soxRS regulon, whose products act collectively to avoid and repair oxidative damage. The aim of this work was to investigate how directed alterations in NADP(H) levels could affect both deployment of the soxRS response and tolerance to MV-driven oxidative stress. E. coli transformation with a plasmid encoding a strong NADPH producer, the non-phosphorylating plant glyceraldehyde 3-phosphate dehydrogenase, led to build-up of NADPH contents, down-regulation of the soxRS response and decreased tolerance to MV. Conversely, incorporation of a NADPH consumer, chloroplast ferredoxin, resulted in the opposite behaviour. These observations indicate that NADP(H) homeostasis plays a critical role in proper execution of the soxRS response.