The Synechocystis PCC6803 MerA-Like Enzyme Operates in the Reduction of Both Mercury and Uranium under the Control of the Glutaredoxin 1 Enzyme.

In a continuing effort to analyze the selectivity/redundancy of the three glutaredoxin (Grx) enzymes of the model cyanobacte- rium Synechocystis PCC6803, we have characterized an enzyme system that plays a crucial role in protection against two toxic metal pollutants, mercury and uranium. The present data show that Grxl (Sir1562 in CyanoBase) selectively interacts with the presumptive mercuric reductase protein (S1r1849). This MerA enzyme plays a crucial role in cell defense against both mercuric and uranyl ions, in catalyzing their NADPH-driven reduction. Like MerA, Grxl operates in cell protection against both mercury and uranium. The Grxl-MerA interaction requires cysteine 86 (C86) of Grxl and C78 of MerA, which is critical for its reductase activity. MerA can be inhibited by glutathionylation and subsequently reactivated by Grxl, likely through deglutathionylation. The two Grxl residues C31, which belongs to the redox active site (CX2C), and C86, which operates in MerA interactions, are both required for reactivation of MerA. These novel findings emphasize the role of glutaredoxins in tolerance to metal stress as well as the evolutionary conservation of the glutathionylation process, so far described mostly for eukaryotes [ABSTRACT FROM AUTHOR]