Antioxidant system of peroxiredoxins in Sulfolobus solfataricus.

The maintenance of the proper intracellular redox environment in aerobic microorganisms is guaranteed by redox systems and antioxidants that safeguard cells from the attack of reactive oxgen species (ROS) such as superoxide anions (O∙-), hydrogen peroxide (H2O2), hydroxyl radicals (OH∙). The increase of ROS concentration inside the cell damage biomolecules, membranes and essential metabolic functions. To kept low the intracellular level of ROS the cells are equipped of an array of antioxidant systems that have in the first line the superoxide dismutase (SODs) that catalyze the dismutation of O∙- to form H2O2 and oxygen. The H2O2 is reduced by different systems represented mainly by catalases and peroxidases. The peroxiredoxins (Prx) are thiol-peroxidase that can scavange the peroxides utilizing generally Thioredoxin Reductase (TR) / Thioredoxin (Trx) system as electron donors that allow the recycling of the enzymes (1). Prxs are ubiquitous enzymes that share the same basic catalytic mechanisms, in which an activated cysteine (the peroxidative cysteine) is oxidized to sulphenic acid by peroxide substrate. Reductive regeneration of the oxidized catalytic thiol generally depends on glutathione, thioredoxin, glutaredoxin, cyclophilin and tryparedoxin. The aim of this project is to expand the knowledge on antioxidant system in Sulfolobus solfataricus. For this purpose we have expressed in E. coli and characterized the four Prxs, Bcp1, Bcp2 (2), Bcp3, Bcp4. The purified recombinant proteins are able to remove both H2O2 and tert-butyl hydroperoxide and show high thermostability. Furthermore Bcp1, Bcp3 and Bcp4 can use as electron donor in the reycling of enzymes, the redox system Protein Disulfide Oxidoreductase (SsPDO) / TR previously characterized in S.solfataricus (3) while Bcp2 can use only DTT. Comparative functional and transcriptional analysis suggest different role of Bcps during oxidative stress: Bcp2 and Bcp3 could act as inducible enzyme when the cell are attacked by exogenous peroxides, while Bcp1 and Bcp4 could support a protective role against endogenous peroxide formed during metabolism.