A glutaredoxin-fused thiol peroxidase acts as an important player in hydrogen peroxide detoxification in late-phased growth of Anabaena sp. PCC7120.

The Anabaena sp. genome contains an open reading frame with homology to a novel hybrid form of thiol peroxidase, fused with a glutaredoxin domain. The gene was expressed in Escherichia coli. The purified hybrid protein exerted the highest peroxidase activity toward H2O2 using an electron from a reduced form of glutathione. The calculated kcat and kcat/K(m) values for H2O2 are 48.2 s(-1) and 3.29 x 10(6) M(-1) s(-1), respectively. Immunoblot analyses of the heterocystic proteins showed that the level of the protein in the heterocyst is comparable to that in the vegetative cell. All oxidants tested significantly elevated the mRNA and protein levels. The transcript slightly increased during the exponential growth phase, following which it increased steeply. Also, the levels of transcript were significantly increased in response to N2 starvation, carbon starvation, and light elimination. Taken together, the present data reveal for the first time that the glutathione-dependent thiol peroxidase is an adaptive strategy in Anabaena sp. that efficiently combats H2O2 that are produced during later phase of vegetative and heterocystic growth.