The possibility of a mercuric ion binding protein MerP as antioxidant

Reactive oxygen species (ROS) are occurred in biological system by the action of mitochondrial electron transport system and nicotinamide adenine dinucleotide phosphate (NADP) oxidase. These oxygen free radicals play a major role in the development of ailments such as cancer and cataracts. On the other hand, there are various antioxidants such as superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), glutathione (GSH) and ascorbic acid (AA) that could mitigate the impact of ROS. Interestingly, some heavy metal binding proteins has been shown to scavenge free radicals as well and this prompted us to examine whether the mercuric ion binding protein (MerP) may play as an antioxidant or not. In this study, a signal peptides defected Bacillus MerP protein was purified from recombinant Escherichia coli host and synthesized oligopeptides that according to the metal binding motif of MerP occurred from either Gram-positive or negative bacteria. The 1,1-diphenyl-picrylhydrazyl radical (DPPH•) and 2,2-azinobis-3-ethylbenzothiazoline -6-sulfonic acid (ABTS•) were used as free radicals and GSH was used as the control antioxidant. Though the free radicals scavenging ratio in DPPH• assay was almost the same between MerP and GSH where MerP was 20% higher than GSH in ABTS•+. The result suggests that MerP can play as an antioxidant. Furthermore, both of the synthesized oligopeptides performed scavenging ability as good as GSH in ABTS• assay and over 30% higher than GSH in DPPH•. Meanwhile, the scavenging abilities were lost while their cysteine residues were replaced by alanine. These results may show the dual functions of those heavy metals binding proteins.