Thioredoxin-dependent hydroperoxide peroxidase activity of bacterioferritin comigratory protein (BCP) as a new member of the thiol-specific antioxidant protein (TSA)/alkyl hydroperoxide peroxidase C (AhpC) family

Escherichia coli bacterioferritin comigratory protein (BCP), a putative bac terial member of the TSA/AhpC family, was characterized as a thiol peroxida se, BCP showed a thioredoxin-dependent thiol peroxidase activity, BCP prefe rentially reduced linoleic: acid hydroperoxide rather than H2O2 and t-butyl hydroperoxide with the use of thioredoxin as an in vivo immediate electron donor. The value of V-max/K-m of BCP for Linoleic acid hydroperoxide was c alculated to be 5-fold higher than that for H2O2, implying that ECP has a s elective capability to reduce linoleic acid hydroperoxide. Replacement of C ys-45 with serine resulted in the complete loss of thiol peroxidase activit y; suggesting that BCP is a new bacterial member of TSA/AhpC family having a conserved cysteine as the primary site of catalysis, BCP exists as a mono mer, and its functional Cys-45 appeared to exist as cysteine sulfenic acid. The expression level of BCP gradually elevated during exponential growth u ntil mid-log phase growth, beyond which the expression level was decreased. BCP was induced 3-fold by the oxidative stress given by changing the growt h conditions from the anaerobic to aerobic culture. Bcp null mutant grew mo re slowly than its wild type in aerobic culture and showed the hypersensiti vity toward various oxidants such as H2O2, t-butyl hgdroperoxide, and linol eic acid hydroperoxide. The peroxide hypersensitivity of the null mutant co uld be complemented by the expression of bcp gene. Taken together, these da ta suggest that BCP is a new member of thioredoxin-dependent TSA/AhpC famil y, acting as a general hydroperoxide peroxidase.