Thioredoxin regulates human mercaptopyruvate sulfurtransferase at physiologically-relevant concentrations

Pramod Kumar Yadav, Victor Vitvitsky, Sebastián Carballal, Javier Seravalli, Ruma Banerjee

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

3-Mercaptopyruvate sulfur transferase (MPST) catalyzes the desulfuration of 3-mercaptopyruvate (3-MP) and transfers sulfane sulfur from an enzyme-bound persulfide intermediate to thiophilic acceptors such as thioredoxin and cysteine. Hydrogen sulfide (H2S), a signaling molecule implicated in many physiological processes, can be released from the persulfide product of the MPST reaction. Two splice variants of MPST, differing by 20 amino acids at the N terminus, give rise to the cytosolic MPST1 and mitochondrial MPST2 isoforms. Here, we characterized the poorly-studied MPST1 variant and demonstrated that substitutions in its Ser–His–Asp triad, proposed to serve a general acid–base role, minimally affect catalytic activity. We estimated the 3-MP concentration in murine liver, kidney, and brain tissues, finding that it ranges from 0.4 μmol kg-1 in brain to 1.4 μmol kg-1 in kidney. We also show that N-acetylcysteine, a widely-used antioxidant, is a poor substrate for MPST and is unlikely to function as a thiophilic acceptor. Thioredoxin exhibits substrate inhibition, increasing the KM for 3-MP ~15-fold compared with other sulfur acceptors. Kinetic simulations at physiologically-relevant substrate concentrations predicted that the proportion of sulfur transfer to thioredoxin increases ~3.5-fold as its concentration decreases from 10 to 1 μM, whereas the total MPST reaction rate increases ~7-fold. The simulations also predicted that cysteine is a quantitatively-significant sulfane sulfur acceptor, revealing MPST’s potential to generate low-molecular-weight persulfides. We conclude that the MPST1 and MPST2 isoforms are kinetically indistinguishable and that thioredoxin modulates the MPST-catalyzed reaction in a physiologically-relevant concentration range.

Original languageEnglish (US)
Pages (from-to)6299-6310
Number of pages12
JournalJournal of Biological Chemistry
Volume295
Issue number19
DOIs
StatePublished - May 8 2020

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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