MPC2

MPC2 is a subunit of the mitochondrial pyruvate carrier (MPC) complex of Toxoplasma gondii, functioning together with MPC1 as a heterodimeric transporter that imports cytosol-derived pyruvate into the mitochondrion and thereby couples glycolysis to the TCA cycle (PMID:36920199). Genetic ablation of MPC2 impairs mitochondrial acetyl-CoA synthesis and globally reduces carbon flux through glycolysis and the TCA cycle, phenocopying loss of branched-chain ketoacid dehydrogenase (BCKDH) and slowing asexual parasite growth (PMID:36920199). Consistent with the metabolic plasticity of the parasite, loss of MPC2 exerts only a modest effect on virulence in mice, indicating that alternative routes can partially compensate for the absence of cytosolic pyruvate import (PMID:36920199). Beyond these transport and metabolic roles, no further mechanistic detail for MPC2 has been characterized in the available corpus.

1. 2023 High

   Whether T. gondii possesses a functional link importing glycolytic pyruvate into the mitochondrion was unresolved; establishing MPC2/MPC1 as a conserved pyruvate carrier defined the missing connection between glycolysis and the TCA cycle.

   Evidence Genetic complementation of a yeast MPC-deficient mutant plus KO of MPC1/MPC2 with 13C-glucose flux tracing in T. gondii

   PMID:36920199

   Open questions at the time

   • No structural model of the MPC1/MPC2 heterodimer or stoichiometry
   • Transport kinetics and substrate specificity not quantified
   • Regulation of carrier assembly/expression unknown
2. 2023 High

   The metabolic consequence of losing pyruvate import was undefined; KO showed MPC2 loss impairs mitochondrial acetyl-CoA synthesis and reduces glycolytic/TCA carbon flux, placing MPC2 upstream in the same pathway as BCKDH.

   Evidence Genetic KO with 13C-glucose metabolic labeling and epistatic comparison against BCKDH mutants

   PMID:36920199

   Open questions at the time

   • Direct demonstration that imported pyruvate feeds BCKDH rather than another enzyme not shown
   • Compensatory carbon sources not identified
3. 2023 Medium

   Whether pyruvate import is essential in vivo was untested; a mouse infection model showed only modest virulence loss, establishing that MPC function is dispensable for infection due to metabolic plasticity.

   Evidence Mouse infection with MPC KO parasites

   PMID:36920199

   Open questions at the time

   • Single-lab in vivo assay demonstrating a modest/negative effect
   • Compensatory pathways sustaining virulence not defined
   • Effect across life-cycle stages not tested

• The structural basis of pyruvate translocation, the stoichiometry and assembly of the MPC1/MPC2 complex, and the identity of compensating metabolic routes remain open.
• No structure or transport mechanism
• Compensatory carbon-source pathways unidentified
• No characterization in other species