PF3D7_0419300

PF3D7_0419300 (PfRad51) is the central recombinase driving homologous-recombination (HR) repair of DNA double-strand breaks in Plasmodium falciparum, with its expression induced by DNA-damaging insult (PMID:14527521) and its activity essential for repair of breaks in the conserved core genome (PMID:41277688). As purified recombinant protein, PfRad51 catalyzes DNA strand exchange without requiring ATP hydrolysis and performs ssDNA-dependent ATP hydrolysis at rates comparable to human Rad51 (PMID:15610817). Its recombinase activity is tuned by accessory factors: PfRad54 accelerates strand exchange as a positive cofactor (PMID:23631919), PfRPA1L stimulates homologous pairing while PfRPA1S antagonizes this stimulation to suppress PfRad51 activity (PMID:23631919), and PfHsp90 physically binds PfRad51 to maintain its stability and prevent proteasomal degradation (PMID:34097485). The ATPase function is mechanistically required in vivo: a dominant-negative ATPase-dead mutant abolishes HR-mediated repair and sensitizes parasites to DNA damage (PMID:25145341), and the inhibitor B02 blocks both enzymatic activities and PfRad51 focus formation, synergizing with antimalarials (PMID:30936202). Beyond genome maintenance, PfRad51-mediated HR generates recombination among var genes, driving antigenic diversification (PMID:37593128), while a Rad51-independent homology-directed pathway handles subtelomeric breaks (PMID:41277688). Physical partnerships with BRCA2 BRC repeats (PMID:35804459), PfBlm helicase (PMID:33239368), and the mitochondrial exonuclease PfExomit2 (PMID:41243319) place PfRad51 within multiple repair contexts.

1. 2003 Medium

   Establishing whether PfRad51 participates in DNA repair at all, its induction by a DNA-damaging agent provided the first functional link to recombinational repair in the parasite.

   Evidence RT-PCR and Western blot of MMS-treated intra-erythrocytic P. falciparum cultures

   PMID:14527521

   Open questions at the time

   • Expression up-regulation is correlative, not a direct demonstration of repair activity
   • Does not establish substrate or mechanism
2. 2005 High

   To determine whether PfRad51 is a bona fide recombinase, purified protein was tested biochemically, confirming ATP-independent strand exchange and ssDNA-dependent ATPase activity comparable to human Rad51.

   Evidence In vitro strand-exchange and ATPase assays with recombinant PfRad51 from E. coli

   PMID:15610817

   Open questions at the time

   • In vitro reconstitution does not establish in vivo requirement
   • Role of ATPase activity in the cell not defined
3. 2013 High

   To identify regulators of PfRad51's recombinase activity, reconstitution with candidate cofactors showed PfRad54 accelerates strand exchange and defined a PfRPA1L/PfRPA1S positive/negative regulatory axis.

   Evidence In vitro DNA pairing/strand-exchange assays with recombinant PfRad51, PfRad54, PfRPA1L, PfRPA1S, plus in vivo comet assay

   PMID:23631919

   Open questions at the time

   • Structural basis of cofactor interactions unresolved
   • In vivo stoichiometry and timing of regulation unknown
4. 2014 High

   To test whether ATPase activity is mechanistically required in vivo, a dominant-negative ATPase-dead mutant was shown to disrupt HR-mediated repair and reduce parasite burden, linking enzymatic function to parasite fitness.

   Evidence Transgenic P. berghei expressing PfRad51(K143R), mouse infection model, and yeast HR/gene-targeting assays

   PMID:25145341

   Open questions at the time

   • Dominant-negative approach does not equate to clean loss of function
   • Mechanism of dominant interference not detailed
5. 2019 High

   To validate PfRad51 as a druggable antimalarial target, the small molecule B02 was shown to inhibit its enzymatic activities and focus formation and to synergize with existing antimalarials.

   Evidence In vitro ATPase/strand-exchange assays, immunofluorescence foci assay, in silico docking, and drug-synergy growth assays in strains 3D7 and Dd2

   PMID:30936202

   Open questions at the time

   • B02 specificity for PfRad51 over other targets not fully excluded
   • Proposed block of homomeric interactions not structurally demonstrated
6. 2021 Medium

   To explain how PfRad51 protein levels are maintained during damage response, PfHsp90 was found to physically bind PfRad51 and prevent its proteasomal degradation, coupling chaperone function to repair capacity.

   Evidence Co-immunoprecipitation, proteasome-inhibitor experiments, DNA-damage sensitivity assays, and B02 synergy in strains 3D7 and Dd2

   PMID:34097485

   Open questions at the time

   • Single-lab Co-IP without reciprocal structural mapping of the interaction
   • Whether Hsp90 also regulates PfRad51 activity beyond stability unclear
7. 2020 Low

   To broaden the PfRad51 interaction network in DSB repair, PfBlm helicase was shown to physically associate with PfRad51.

   Evidence Co-immunoprecipitation/pulldown between PfBlm and PfRad51

   PMID:33239368

   Open questions at the time

   • Single pulldown without reciprocal validation
   • Functional consequence of the PfBlm-PfRad51 interaction for repair not defined
   • Direct vs. indirect interaction not distinguished
8. 2022 Medium

   To test conservation of the BRCA2-Rad51 axis, P. berghei BRCA2 BRC repeats were shown to interact with the PbRad51 ortholog, indicating the loading regulator is conserved in Plasmodium.

   Evidence Mammalian two-hybrid assay with BRCA2 BRC repeats, plus BRCA2 knockout phenotyping in mice and mosquitoes

   PMID:35804459

   Open questions at the time

   • Interaction shown by a single two-hybrid method in a heterologous system
   • Interaction demonstrated for the P. berghei ortholog, not directly for PF3D7_0419300
   • Functional effect on PfRad51 loading not measured
9. 2023 Medium

   To determine a physiological role of PfRad51-mediated HR beyond genome maintenance, loss of recombinase function was shown to reduce var gene recombination, implicating PfRad51 in antigenic diversification.

   Evidence Whole-genome sequencing of PfRad51-proficient vs. -deficient lines over ~100 generations comparing var rearrangement rates

   PMID:37593128

   Open questions at the time

   • Single-lab, single-study observation
   • Mechanistic link between recombinase activity and var-specific rearrangement not detailed
10. 2025 High

    To define which genomic regions depend on PfRad51, knockout parasites revealed PfRad51 is essential for core-genome DSB repair while a Rad51-independent pathway handles subtelomeric breaks, partitioning repair by chromosomal domain.

    Evidence PfRad51 knockout lines, targeted DSB assay, cell-cycle-resolved irradiation hypersensitivity, and comparison with TLS polymerase knockouts

    PMID:41277688

    Open questions at the time

    • Molecular identity of the Rad51-independent subtelomeric pathway not established
    • Factors directing domain-specific pathway choice unknown
11. 2025 Low

    To extend PfRad51's repair contexts to the organelle, PfRad51 was found to interact with the mitochondria-targeted exonuclease PfExomit2, hinting at a role in mitochondrial DSB repair.

    Evidence Pull-down assay between PfExomit2 and PfRad51

    PMID:41243319

    Open questions at the time

    • Single pulldown without reciprocal validation
    • Mitochondrial localization of PfRad51 itself not directly confirmed
    • Functional role in mitochondrial repair not demonstrated

• The molecular identity of the Rad51-independent subtelomeric repair pathway and the structural basis by which cofactors (Rad54, RPA1L/S, BRCA2, Hsp90) coordinate PfRad51 filament assembly remain unresolved.
• No structural model of PfRad51 filaments or cofactor complexes
• Mechanism of chromosomal-domain-specific pathway choice unknown
• Direct evidence for PfRad51 in mitochondrial repair lacking