Modulation of chloroplast 2-Cys Peroxiredoxin activities by nucleotides

ARAN, MARTIN; ETCHEGOREN, JUAN I.; CAPORALETTI, DANIEL; SENN, ALEJANDRO: TELLEZ DE IÑON, MARÍA T. AND WOLOSIUK, RICARDO A.

Pinamar, Argentina.

Congreso; XLI SAIB ANNUAL MEETING; 2005

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Peroxiredoxins (Prx) are ubiquitous peroxidases that play an important role in controlling diverse cellular functions. Members of this protein family devoid of heme prosthetic group contain either one (1-Cys) or two (2-Cys) conserved cysteine residues for functioning in the peroxidatic activity using reduced thioredoxin and flavoprotein reductases (i.e. AhpF) as electron donors. X-ray crystal structures of human erythrocytes and Crithidia fasciculata 2-Cys Prx evinced the noncovalent association of five homodimers; i.e. [(Prx)2]5. We found previously that a chaperone activity is associated to the peroxidase activity in the chloroplast 2-Cys Prx from rapeseed (Brassica napus). In this context, we deemed it desirable to analyze whether chloroplast metabolites affect these activities. The concerted action of ATP and Mg2+ inhibited both the peroxidase and the chaperone activities of chloroplast 2-Cys Prx. Germane to this feature, ATP quenched partially the intrinsic emission fluorescence which, as revealed by site-directed mutagenesis studies, arose from interactions with the conserved tryptophan residue located at a C-terminal loop near the Cys175 and an internal cavity (Trp179) but not with the other placed in contact with the solvent (Trp88). Notably, as result of this interaction, ATP transfers the γ-phosphate to the oxidized protein but not to the reduced counterpart. These results illustrated the modulation of chloroplast 2-Cys Prx functions via noncovalent interactions and covalent modifications elicited by ATP which are relevant in the regulation of the oxidative stress.