GyrB

GyrB (PF3D7_1239500) is a functional DNA gyrase B subunit of Plasmodium falciparum that supplies the ATPase activity of an apicoplast-localized gyrase and is required for apicoplast DNA replication (PMID:17220464, PMID:17499371). Recombinant PfGyrB displays strong intrinsic ATPase activity, complements an E. coli gyrase temperature-sensitive strain, and reconstitutes DNA cleavage activity together with the N-terminal domain of PfGyrA, confirming it acts as a genuine gyrase subunit; distinctively, it undergoes ATP-independent dimerization not seen in E. coli GyrB (PMID:17220464). Its ATPase activity is inhibited by the bacterial gyrase inhibitor novobiocin, and novobiocin treatment of cultured parasites lowers the apicoplast/nuclear DNA ratio, tying GyrB function to apicoplast genome maintenance (PMID:17499371). The enzyme is amenable to hybrid reconstitution with E. coli GyrA, in which purpurogallin preferentially inhibits the hybrid by disrupting DNA binding and thereby the DNA-stimulated ATPase activity of PfGyrB (PMID:34339271). GyrB's druggable ATPase activity makes it an antimalarial target, with additional inhibitors (UNC8153, fexofenadine) showing antiplasmodial activity including against an artemisinin-resistant strain (PMID:42482438). Beyond these enzymatic and pharmacological characterizations, no further mechanistic detail (e.g., in-parasite genetic knockout or structural determination) has been characterized in the available corpus.

1. 2005 Medium

   Establishing that the Plasmodium GyrB ATP-binding domain is an active, drug-sensitive ATPase addressed whether the parasite encodes a genuine gyrase B enzymatic module.

   Evidence Recombinant 43 kDa ATP-binding domain of P. vivax GyrB (ortholog of PF3D7_1239500) characterized by in vitro ATPase kinetics and coumermycin inhibition

   PMID:15694492

   Open questions at the time

   • Shown for the P. vivax ortholog, not directly for PF3D7_1239500
   • Only the isolated ATP-binding domain, not full-length or holoenzyme
   • No demonstration of gyrase supercoiling or GyrA partnership
2. 2007 High

   Direct enzymatic reconstitution and complementation established PfGyrB as a bona fide gyrase subunit and revealed a parasite-specific ATP-independent dimerization property.

   Evidence Recombinant PfGyrB ATPase assay, E. coli gyrase ts-strain complementation, and DNA cleavage reconstitution with the N-terminal domain of PfGyrA

   PMID:17220464

   Open questions at the time

   • Full supercoiling reconstitution with native PfGyrA not shown
   • Functional significance of ATP-independent dimerization unresolved
   • No in-parasite genetic evidence of essentiality
3. 2007 High

   Linking GyrB inhibition to a fall in the apicoplast/nuclear DNA ratio connected the enzyme's biochemical activity to its cellular role in apicoplast DNA replication.

   Evidence In vitro novobiocin ATPase inhibition, apicoplast/nuclear DNA ratio measurement in novobiocin-treated cultures, anti-PfGyrB immunoblotting, and molecular modeling of the ATPase domain

   PMID:17499371

   Open questions at the time

   • Apicoplast DNA effect is pharmacological, not from a GyrB-specific genetic perturbation
   • Subcellular localization inferred from function/modeling rather than imaging
   • Role of the unique disordered loop not tested
4. 2021 High

   A hybrid PfGyrB/E. coli GyrA enzyme provided a tractable system to dissect a parasite-selective inhibitor's mechanism, showing inhibition proceeds through disrupted DNA binding and reduced DNA-stimulated ATPase activity.

   Evidence Hybrid enzyme reconstitution, supercoiling and ATPase assays, and binding-affinity measurements with purpurogallin

   PMID:34339271

   Open questions at the time

   • Uses E. coli GyrA rather than native PfGyrA
   • Selectivity and efficacy against live parasites via this mechanism not established here
   • No structural model of the PfGyrB-inhibitor interaction
5. 2026 Medium

   Screening-derived ATPase inhibitors with antiplasmodial activity, including against an artemisinin-resistant strain, extended GyrB's status as an actionable antimalarial drug target.

   Evidence Virtual screening, biochemical ATPase inhibition, and parasite growth/morphology assays with UNC8153 and fexofenadine against wild-type and C580Y strains

   PMID:42482438

   Open questions at the time

   • No mechanistic follow-up beyond ATPase inhibition
   • On-target engagement in parasites not confirmed
   • Selectivity over host targets not addressed

• Whether PfGyrB is genetically essential in the parasite and how the holoenzyme is structurally organized and targeted to the apicoplast remain unresolved.
• No conditional knockout/knockdown of PF3D7_1239500 in the corpus
• No experimental structure of PfGyrB or the PfGyrA/PfGyrB holoenzyme
• Apicoplast import signal and trafficking not directly characterized