Exploring the antioxidant system of Sulfolobus solfataricus : structural and functional analysis of peroxiredoxin Bcp1.

Peroxiredoxins (Prx) are non-haem-containing peroxidases that generally catalyze the reduction of peroxides to the corresponding alcohols through a peroxidatic cysteine (Cysp) that becomes oxidized to a sulfenic acid during the catalytic process [1]. In the recent years, these proteins have received considerable attention as consequence of their involvement in different cellular processes ranging from antioxidant defence, redox homeostasis, to parasite drug resistance, cancer and H2O2 –mediated cellular signalling. Our studies are focused on peroxiredoxin system in <i>Sulfolobus solfataricus </i>, an aerobic hypethermophilic archaeon growing at 85°C. Recently we characterized four Prxs called, Bcp1, Bcp2, Bcp3 and Bcp4: two of these, Bcp2 and Bcp3, are inducible by oxidative stress whereas Bcp1 and Bcp4 are expressed constitutively. Functional studies showed that all Bcps have antioxidant activity scavenging both H2O2 and organic peroxides [2,3]. The catalytic mechanism of Bcp1was obtained through site-directed mutagenesis, functional analysis and structural studies by crystallization and X ray-diffraction. The data showed that Bcp1 can be classified in the 2-Cys atypical Prx class. The catalytic mechanism involves the oxidation of the Cysp (C45) into sulfenic acid in presence of peroxide and the formation of intramolecular disulfide bond between the Cysp and the resolving cysteine (C50). The reduction of disulfide bond involves a peculiar oxidoreductase system based on: the Protein Disulfide Oxidoreductase SsPDO (Sso0192) [4, 5], the Thioredoxin reductase SsTr (Sso2416) and NADPH. This is the first archaeal peroxiredoxin belonging to 2-Cys atypical class to be crystallized and the structure to be resolved