Glyceraldehyde 3-phosphate dehydrogenase converts methylmercury to its sulfur adduct with lowered toxicity through sulfane sulfur atoms on Cys247

Abstract

Methylmercury (MeHg) reacts with nucleophilic sulfur species to form sulfur adducts, such as the low-toxic metabolite bismethylmercury sulfide [(MeHg)₂S]. We found that protein-bound persulfides interact with MeHg to form (MeHg)₂S and identified glutathione S-transferase pi 1 as a S-sulfhydrated protein involved in (MeHg)₂S formation. Although glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a house-keeping protein abundantly expressed in various tissues, has been reported to undergo S-sulfhydration in the presence of sulfur donors or cystathionine γ-lyase, the biological significance of this post-translational modification is poorly understood. In this study, we investigated the possible interaction between GAPDH and MeHg to form (MeHg)₂S. High-performance liquid chromatography/atomic absorption spectrophotometry revealed that (MeHg)₂S was formed during the reaction of MeHg with a model of cysteine persulfide and GAPDH following incubation of the protein with NaHS. After reacting with NaHS, GAPDH C152S and C156S mutants transformed MeHg into (MeHg)₂S, whereas formation of the sulfur adduct was not observed for the C247S mutant, suggesting that Cys247 is critical for conversion of MeHg to (MeHg)₂S. These results suggest that the sulfane sulfur on Cys247 of GAPDH plays a protective role in reducing MeHg toxicity.