PrxQ-A, a member of the peroxiredoxin Q family, plays a major role in defense against oxidative stress in the cyanobacterium Anabaena sp. strain PCC7120

Abstract: The genome of the cyanobacterium Anabaena PCC 7120 encodes seven polypeptides showing sequence similarities with peroxiredoxins (Prx-s). One of them, prxQ-A (alr2503), which encodes a Prx Q homologue, is located in the same gene cluster as pkn22, which encodes a Ser/Thr kinase. Here we report that the pkn22-knockout mutant (Mp22) is sensitive to oxidative stress because it fails to synthesize PrxQ-A; the expression of prxQ-A is significantly induced under oxidative stress conditions. The hypersensitivity of the Mp22 mutant to oxidative stress was restored by inducing the expression of the prxQ-A gene in trans. The recombinant PrxQ-A protein shows antioxidant activity protecting the DNA from being degraded by reactive oxygen species, catalyzes the reduction of H2O2 in the presence of DTT, and shows thioredoxin-dependent peroxidase activity in vitro. The conserved Cys47 residue is the peroxide oxidation site, since the replacement of Cys47 by a Ser residue completely abolished the peroxidase activity. All these data suggest that PrxQ-A may efficiently protect this organism from oxidative stress. [Copyright &y& Elsevier]