BCKDH-E2

BCKDH-E2 (PF3D7_0303700) is the E2 lipoamide acyltransferase subunit of the mitochondrial branched-chain keto acid dehydrogenase (BCKDH) complex in Plasmodium, where the complex functions in the parasite as the enzyme that generates acetyl-CoA for central carbon metabolism (PMID:25032958, PMID:37068227). In P. berghei, BCKDH substitutes for the missing mitochondrial pyruvate dehydrogenase by converting pyruvate to acetyl-CoA feeding the TCA cycle, and this activity is required for blood-stage development and for oocyst maturation during mosquito transmission (PMID:25032958). The E2 subunit itself localises to the P. falciparum mitochondrion (PMID:25116855) and is activated by lipoylation through a distinctive two-component mechanism: neither LipL1 nor LipL2 alone can modify BCKDH-E2, but together they lipoylate it exclusively under strongly reducing conditions, a redox-gated route distinct from the H-protein lipoylation pathway (PMID:25116855). Functionally, BCKDH-E2 and the α-ketoglutarate dehydrogenase E2 subunit (KDH) are synthetically lethal in P. falciparum—single deletions are tolerated but simultaneous loss is not—establishing that the two ketoacid dehydrogenases together supply the mitochondrial acetyl-CoA pool required for survival, with LipL2-dependent lipoylation being necessary for BCKDH activity (PMID:37068227). This mitochondrial acetyl-CoA in turn is required for histone and other protein acetylation outside the mitochondrion, linking BCKDH-E2 metabolism to nuclear/cytosolic acetylation essential for the parasite (PMID:37068227). Beyond its role as a lipoylated E2 subunit of this complex, no further mechanistic detail specific to PF3D7_0303700 has been characterized in the available corpus.

1. 2014 Medium

   Establishing that in Plasmodium the BCKDH complex, of which BCKDH-E2 is the acyltransferase subunit, performs the pyruvate-to-acetyl-CoA reaction normally assigned to pyruvate dehydrogenase, and that this is required for transmission.

   Evidence Genetic deletion of the BCKDH E1a subunit (partner of E2) in P. berghei with growth, virulence, oocyst, and metabolite readouts

   PMID:25032958

   Open questions at the time

   • BCKDH-E2 was inferred as a complex member, not directly manipulated
   • Does not resolve the specific catalytic contribution of the E2 subunit versus other subunits
   • Shown in P. berghei; not tested in P. falciparum here
2. 2014 High

   Determining where the E2 subunit acts and how it is post-translationally activated resolved that BCKDH-E2 is mitochondrial and is lipoylated by a novel redox-gated two-enzyme mechanism.

   Evidence Fluorescence localisation and in vitro lipoylation reconstitution with purified LipL1 and LipL2 under defined redox conditions in P. falciparum

   PMID:25116855

   Open questions at the time

   • Structural basis of LipL1/LipL2 cooperativity not defined
   • Physiological redox trigger for lipoylation in vivo not established
   • Localisation shown in a single study/lab
3. 2023 High

   Testing whether the two mitochondrial ketoacid dehydrogenases are individually essential revealed a synthetic lethal relationship, defining BCKDH-E2 together with KDH as the source of an essential mitochondrial acetyl-CoA pool.

   Evidence Genetic epistasis (synthetic lethality) with isotope tracing of acetyl-CoA metabolism in P. falciparum

   PMID:37068227

   Open questions at the time

   • Does not isolate the BCKDH-E2 contribution independently of the full complex
   • Quantitative partition of acetyl-CoA flux between BCKDH and KDH not resolved
4. 2023 Medium

   Linking mitochondrial output to gene regulation showed that acetyl-CoA generated by BCKDH/KDH is required for extra-mitochondrial histone and protein acetylation, connecting central metabolism to epigenetic regulation.

   Evidence Metabolite labelling and genetic deletion with measurement of histone/protein acetylation in dehydrogenase-disrupted P. falciparum lines

   PMID:37068227

   Open questions at the time

   • BCKDH-E2 contribution inferred as part of the complex, not directly manipulated alone
   • Mechanism of acetyl-CoA export from mitochondrion not defined
   • Which acetylation targets are functionally decisive not established

• How BCKDH-E2 (PF3D7_0303700) functions in isolation—its individual catalytic activity, structure, and any role separate from KDH-dependent acetyl-CoA supply—remains uncharacterized.
• No structure of BCKDH-E2 in the corpus
• No direct measurement of its acyltransferase activity alone
• Regulation of its expression or turnover unknown