Dual functions of Arabidopsis sulfiredoxin: Acting as a redox-dependent sulfinic acid reductase and as a redox-independent nuclease enzyme

Based on the fact that the amino acid sequence of sulfiredoxin (Srx), already known as a redox-dependent sulfinic acid reductase, showed a high sequence homology with that of ParB, a nuclease enzyme, we examined the nucleic acid binding and hydrolyzing activity of the recombinant Srx in Arabidopsis (AtSrx). We found that AtSrx functions as a nuclease enzyme that can use single-stranded and double-stranded DNAs as substrates. The nuclease activity was enhanced by divalent cations. Particularly, by point-mutating the active site of sulfinate reductase, Cys (72) to Ser (AtS-rx-C72S), we demonstrate that the active site of the reductase function of AtSrx is not involved in its nuclease function. (C) 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.