MPST

MPST (TUM1) is a rhodanese-family 3-mercaptopyruvate sulfurtransferase that converts 3-mercaptopyruvate to pyruvate and a protein-bound persulfide, providing a major enzymatic source of H2S and reactive sulfur in mammalian cells (PMID:25336638, PMID:26519030). It is expressed as two splice isoforms with distinct compartmentalization—a cytosolic-only form and a form distributed between cytosol and mitochondria—both of which are catalytically active (PMID:25336638). Through physical interaction with the cysteine desulfurase NFS1 and the rhodanese-like protein MOCS3, MPST channels sulfur into molybdenum cofactor biosynthesis and cytosolic tRNA thiomodification, and its loss reduces sulfite oxidase activity, sulfur-modified tRNA levels, H2S output, and cellular bioenergetics (PMID:25336638, PMID:36671528). The persulfide/H2S it generates supports mitochondrial function: MPST loss activates HIF1α, downregulates TIM/TOM import translocase subunits, and suppresses the TCA cycle, oxidative phosphorylation, and fatty acid oxidation, a defect reversible by sulfide donors (PMID:35616614). MPST-derived H2S is the principal sulfide source in coronary artery, where it modulates vasoreactivity through direct chemical reaction with NO (PMID:26519030), and chronic combined H2S deficiency adaptively upregulates the NO/cGMP pathway (PMID:36860295). MPST also directly binds AKT to suppress its phosphorylation, protecting intestinal epithelial cells from apoptosis (PMID:36126419). A nonsense mutation (Tyr85Stop) abolishes enzymatic activity, defining residues required for catalysis (PMID:16545926).

1. 2006 Medium

   Established that specific protein sequence is required for MPST catalytic activity by showing a truncating mutation abolishes function, linking genotype to enzymatic loss.

   Evidence Heterologous expression of a Tyr85Stop variant plus erythrocyte MPST activity measurement

   PMID:16545926

   Open questions at the time

   • No structure-function mapping of which catalytic step the truncation eliminates
   • Clinical phenotype of carriers not defined
2. 2012 Medium

   Resolved the structural architecture of the MPST ortholog, showing two rhodanese-like domains with a single active-site cysteine in the C-terminal domain that mediates sulfur transfer.

   Evidence X-ray crystallography of yeast Tum1 at 1.90 Å

   PMID:22587783

   Open questions at the time

   • Functional validation of the active-site cysteine not performed
   • Identity of unassigned electron density near the active site unknown
3. 2014 High

   Defined MPST isoform compartmentalization and its physical partners, establishing it as a dual cytosolic/mitochondrial sulfurtransferase feeding sulfur-trafficking complexes.

   Evidence Recombinant isoform kinetics, fluorescence localization, in vitro pulldown and split-EGFP interaction with NFS1 and MOCS3

   PMID:25336638

   Open questions at the time

   • Stoichiometry and regulation of the NFS1/MOCS3 sulfur-relay not resolved
   • Functional difference between the two isoforms beyond localization unclear
4. 2015 High

   Identified MPST as the dominant H2S source in coronary artery and clarified that its product modulates vascular tone via direct reaction with NO rather than a single fixed effect.

   Evidence H2S production assays from arterial homogenates, ex vivo vasoreactivity, CSE knockout controls, in vitro H2S–NO reaction

   PMID:26519030

   Open questions at the time

   • Molecular identity of the H2S–NO reaction product in tissue not defined
   • Receptor/channel targets downstream of the H2S–NO interaction not mapped
5. 2022 Medium

   Connected MPST to mitochondrial protein import and oxidative metabolism, showing sulfide supply maintains TIM/TOM translocase expression and energy metabolism.

   Evidence Mpst knockout mouse on high-fat diet, TIM/TOM Western blots, respiratory/flux measurements, sulfide donor rescue

   PMID:35616614

   Open questions at the time

   • Mechanism by which sulfide controls HIF1α/TIM-TOM expression not defined
   • Direct persulfidation targets in import machinery not identified
6. 2022 Medium

   Placed MPST upstream of AKT in an anti-apoptotic pathway by direct binding that suppresses AKT phosphorylation in intestinal epithelium.

   Evidence Co-IP, phosphorylation assays, siRNA/overexpression and AKT epistasis in HT29 cells, DSS colitis mouse model

   PMID:36126419

   Open questions at the time

   • Single Co-IP without reciprocal/structural validation of direct binding
   • Whether suppression depends on persulfidation of AKT not established
7. 2023 Medium

   Confirmed in human cells that MPST is required for molybdenum cofactor biosynthesis and tRNA thiolation, validating its sulfur-donor role beyond interaction data.

   Evidence CRISPR knockout in HEK293, sulfite oxidase activity, LC quantification of thio-modified tRNA, H2S measurement

   PMID:36671528

   Open questions at the time

   • Relative contribution of MPST versus alternative sulfur donors not quantified
   • Single-lab, single cell line
8. 2023 Medium

   Revealed adaptive crosstalk between H2S and NO signaling, where chronic combined H2S deficiency upregulates eNOS and sGC to enhance vasorelaxation.

   Evidence Cth/Mpst double knockout mouse, aortic ring relaxation, blood pressure telemetry, eNOS/sGC Western blots, NOS inhibitor pharmacology

   PMID:36860295

   Open questions at the time

   • MPST-specific contribution not separable from CTH in the double knockout
   • Signaling mechanism driving NO/cGMP upregulation not defined
9. 2025 Medium

   Extended MPST's mitochondrial-metabolic requirement to airway epithelial development, where its loss impairs ciliated differentiation and respiration.

   Evidence RNAi knockdown in patient-derived airway epithelial 3D ALI cultures, RNA-seq, Seahorse flux, ciliated-cell immunofluorescence (preprint)

   PMID:41509323

   Open questions at the time

   • Preprint, single lab, no replication
   • Whether the defect is sulfide-dependent and rescuable not tested

• How MPST partitions its persulfide output among Moco/tRNA sulfur trafficking, mitochondrial import maintenance, AKT regulation, and vascular signaling within a single cell remains unresolved.
• No unifying model connecting MPST's enzymatic persulfide chemistry to its distinct downstream phenotypes
• Direct persulfidation targets across these pathways not catalogued