Escherichia coli Periplasmic Thiol Peroxidase Acts as Lipid Hydroperoxide Peroxidase and the Principal Antioxidative Function during Anaerobic Growth

Abstract

To clarify the enzymatic property of Escherichia coli periplasmic thiol peroxidase (p20), the specific peroxidase activity toward peroxides was compared with other bacterial thiol peroxidases. p20 has the most substrate preference and peroxidase activity toward organic hydroperoxide. Furthermore, p20 exerted the most potent lipid peroxidase activity. Despite that the mutation of p20 caused the highest susceptibility toward organic hydroperoxide and heat stress, the cellular level of p20 did not respond to the exposure of oxidative stress. Expression level of p20 during anaerobic growth was sustained at the ∼50% level compared with that of the aerobic growth. Viability of aerobic p20Δ without glucose was reduced to the ∼65% level of isogenic strains, whereas viability of aerobic p20Δ with 0.5% glucose supplement was sustained. The deletion of p20 resulted in a gradual loss of the cell viability during anaerobic growth. At the stationary phase, the viability of p20Δ was down to ∼10% level of parent strains. An analysis of the protein carbonyl contents of p20Δ as a marker for cellular oxidation indicates that severe reduction of viability of anaerobic p20Δ was caused by cumulative oxidative stress. P20Δ showed hypersensitivity toward membrane-soluble organic hydroperoxides. An analysis of protein carbonyl and lipid hydroperoxide contents in the membrane of the stress-imposed p20Δ demonstrates that the severe reduction of viability was caused by cumulative oxidative stress on the membrane. Taken together, present data uncover in vivo function for p20 as a lipid hydroperoxide peroxidase and demonstrate that, as the result, p20 acts as the principal antioxidant in the anaerobic habitats.