PyrK

PyrK (PF3D7_0626800) is a glycolytic pyruvate kinase expressed during the intraerythrocytic stages of Plasmodium falciparum that catalyzes the phosphoenolpyruvate/ADP reaction as an active homotetramer with hyperbolic kinetics (PEP Km = 0.19 mM, ADP Km = 0.12 mM) (PMID:15567170). Its allosteric regulation departs from canonical human pyruvate kinases: it is activated by glucose-6-phosphate, which raises apparent maximal velocity, and is inhibited by ATP (competitive with PEP) and citrate (non-competitive, shifting PEP kinetics from hyperbolic to sigmoidal) (PMID:15567170, PMID:32878705). The active R-state and inactive T-state crystal structures define a 'rock-and-lock' mechanism in which rigid-body rotation of each tetramer subunit gates activity (PMID:32878705). Substrate binding and catalytic integrity depend on the A-domain cysteines C49 and C343, whose mutation causes conformational changes, altered substrate affinity, and reduced activity (PMID:35998635). PyrK is also subject to reversible redox control through S-glutathionylation, which inhibits the enzyme and is reversed by P. falciparum glutaredoxin 1, thioredoxin 1, and plasmoredoxin (PMID:21595565). The trypanosome drug suramin inhibits PyrK, and effector-binding-site divergence from human isoforms marks it as a potential antimalarial target (PMID:32878705, PMID:17298920). No physical partners or complex membership of PyrK itself have been characterized in the available corpus beyond its enzymatic deglutathionylation by thioredoxin-family enzymes.

1. 1988 Low

   Established that P. falciparum infection introduces a parasite-specific pyruvate kinase activity into the host erythrocyte, motivating molecular characterization of a distinct parasite enzyme.

   Evidence Enzymatic activity assay and gel electrophoresis of PK activity in infected versus uninfected red cells

   PMID:3058230

   Open questions at the time

   • Indirect evidence from mixed cell populations; the parasite enzyme was not molecularly identified
   • Cannot distinguish PyrK from other pyruvate kinase isoforms
2. 2005 High

   Answered what the recombinant parasite enzyme is and how it behaves kinetically, showing PyrK is an active homotetramer with an unusual regulatory profile distinct from most pyruvate kinases.

   Evidence Recombinant expression, in vitro kinetic and inhibitor assays

   PMID:15567170

   Open questions at the time

   • Regulation reported here as insensitive to G6P, later refined by structural study
   • No structural basis for allostery yet
   • Cellular/in vivo role not addressed
3. 2006 Low

   Confirmed PyrK is actively transcribed during blood stages and that its effector-binding sites diverge from human pyruvate kinases, framing it as a candidate drug target.

   Evidence RT-PCR transcript detection and bioinformatic sequence/phylogenetic analysis

   PMID:17298920

   Open questions at the time

   • Transcript detection only, no protein-level functional data in this study
   • Does not establish differential druggability experimentally
4. 2011 Medium

   Revealed a redox regulatory layer, showing PyrK activity is reversibly inhibited by S-glutathionylation and restored by parasite thioredoxin-family enzymes.

   Evidence Enzymatic deglutathionylation assays with glutaredoxin 1, thioredoxin 1, and plasmoredoxin; proteomic identification

   PMID:21595565

   Open questions at the time

   • Specific modified cysteines not mapped in this study
   • Physiological trigger and in vivo relevance of the modification unresolved
5. 2020 High

   Provided the structural basis for allostery, defining a 'rock-and-lock' R/T-state mechanism and identifying G6P as an activator and suramin as an inhibitor.

   Evidence X-ray crystallography with oxalate/ATP ligands, kinetic and inhibitor assays

   PMID:32878705

   Open questions at the time

   • Suramin selectivity over human enzymes and in-cell efficacy not established
   • Physiological signal driving R/T transition in the parasite unknown
6. 2022 High

   Pinpointed the molecular determinants of catalytic integrity, showing A-domain cysteines C49 and C343 are required for proper substrate binding and phosphate transfer.

   Evidence Site-directed mutagenesis (C49A, C343A), enzymatic assays, and X-ray crystallography of mutants

   PMID:35998635

   Open questions at the time

   • Does not directly link these cysteines to the S-glutathionylation site
   • No cellular validation of mutant phenotypes in parasites

• Whether PyrK is essential for blood-stage growth in vivo, its physical partners, and whether suramin or cysteine-directed inhibitors can be developed into selective antimalarials remain unaddressed in the available corpus.
• No genetic knockout/knockdown of PyrK reported
• No interaction partners or complex membership established for PyrK itself
• Druggability of PyrK-selective inhibitors not tested in parasites