Exploring the catalytic mechanism of the first dimeric Bcp: Functional, structural and docking analyses of Bcp4 from Sulfolobus solfataricus.

The detoxification from peroxides in Sulfolobus solfataricus is performed by the Bacterioferritin comigratory proteins (Bcps), Bcp1 (Sso2071), Bcp2 (Sso2121), Bcp3 (Sso2255) and Bcp4 (Sso2613), antioxidant enzymes belonging to one of the subfamilies of the Peroxiredoxins. In this paper we report on thefunctional, structural and docking analyses of Bcp4, characterized by the CXXXXC motif in the active site. Bcp4 represents the first dimeric Bcp so far investigated. Biochemical studies showed that the protein has a non-covalent dimeric structure and adopts an atypical 2-Cys catalytic mechanism. The X-ray structure of the double mutant C45S/C50S, representative of the fully reduced enzyme state, described the protein dimeric arrangement. Finally, concurrent availability of the crystallographic structure of the monomericBcp1 allowed comparative analysis of the interaction with Protein Disulfide Oxidoreductase SsPDO (Sso0192), involved in the reduction of both Bcp1 and Bcp4, through a proteineprotein docking approach.