Affinage · Plasmodium

PREX

PF3D7_1411400 · plastid replication-repair enzyme

Annotated
2026-09-08
14 papers in source corpus 14 papers cited in narrative 14 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PREX (PF3D7_1411400) is a nuclear-encoded, multi-domain enzyme that provides the core catalytic machinery for replication of the P. falciparum apicoplast genome, uniquely encoding contiguous DNA primase, DNA helicase, family-A DNA polymerase, and 3'→5' proofreading exonuclease activities in a single polypeptide (PMID:15926203). An N-terminal bipartite leader targets PREX specifically to the apicoplast rather than the mitochondrion, where the protein is proteolytically matured into its component functional modules and localizes to dynamic foci (PMID:15926203, PMID:21856338); its minimal primase domain contains functional zinc-binding and TOPRIM folds sufficient to synthesize RNA primers from single-stranded templates (PMID:21856338). Failure to disrupt the P. yoelii orthologue indicates PREX is essential (PMID:21856338). The polymerase domain synthesizes DNA with high fidelity governed principally by mismatch-extension selectivity and proofreading (PMID:24147857), can perform strand-displacement synthesis (PMID:24687154), and protects the AT-rich apicoplast genome by both misincorporating and then proofreading-out oxidized nucleotides such as 8oxodGTP (PMID:32636411) and by error-prone translesion synthesis past oxidative lesions using the fingers-subdomain residues N505 and Y509 that are unique among A-family polymerases (PMID:35220686). Transient-state kinetics and cryo-EM ternary structures show the polymerase has intrinsically low processivity and lacks structural elements for processive synthesis, implying it operates with accessory factors within a replisome (PMID:36251801, PMID:39490679); consistent with this, PREX physically interacts with PfSSB, which modulates its helicase activity (PMID:24267922), and with a novel apicoplast flap endonuclease PfExo implicated in lagging-strand processing (PMID:38888125). The polymerase domain has been structurally resolved by X-ray crystallography and cryo-EM and validated as a druggable antimalarial target through inhibitor screening and structure-activity studies (PMID:27487482, PMID:36191407, PMID:39490679).

Mechanistic history

Synthesis pass · year-by-year structured walk · 14 steps
  1. 2005 High

    Establishing what enzyme replicates the apicoplast genome, this work showed PREX is a single polypeptide carrying primase, helicase, polymerase, and exonuclease activities and is targeted to the apicoplast, defining the organelle's replication engine.

    Evidence Biochemical activity assays, phylogenetic analysis, and GFP reporter localization in P. falciparum

    PMID:15926203

    Open questions at the time
    • Did not establish how the multi-domain protein is processed or coordinated in vivo
    • No structural information on any domain
    • Essentiality not tested
  2. 2009 Medium

    To test whether PREX is a general apicomplexan feature, orthologue analysis showed PREX and its bipartite targeting sequence are conserved in plastid-bearing apicomplexans but absent from plastid-lacking Cryptosporidium, tying PREX function to the plastid.

    Evidence Bioinformatic orthologue identification, targeting-sequence marker delivery, and bacterial expression of the T. gondii polymerase domain

    PMID:19402939

    Open questions at the time
    • Functional conservation shown only for polymerase domain, not full enzyme
    • P. falciparum PREX itself not the direct subject of the orthologue enzymology
  3. 2011 High

    Resolving whether the primase module is self-sufficient and whether PREX matters for viability, the minimal primase domain was shown to make RNA primers, PREX was found to be proteolytically matured into separated domains, and knockout failure indicated essentiality.

    Evidence Recombinant primase assay, maturation analysis, GFP live imaging in P. falciparum, and knockout attempts in P. yoelii

    PMID:21856338

    Open questions at the time
    • Physiological consequence of domain separation by maturation unclear
    • Essentiality inferred from failed knockout, not conditional depletion
  4. 2011 High

    To characterize replication fidelity, the polymerase domain was shown to have a biased mutational spectrum and to functionally complement an E. coli Pol I mutant, confirming genuine, conserved polymerase function.

    Evidence LacZ forward-mutation assay, nucleotide incorporation kinetics, and E. coli Pol I temperature-sensitive complementation

    PMID:21570407

    Open questions at the time
    • Complementation in E. coli does not model the AT-rich apicoplast context
    • Fidelity contribution of proofreading not yet dissected
  5. 2013 High

    Dissecting the determinants of accuracy, comprehensive kinetics across all 12 mismatches identified mismatch extension as the dominant fidelity checkpoint, with modest proofreading variation, defining how PREX achieves accurate synthesis.

    Evidence In vitro kinetic misincorporation, mismatch-extension, and exonuclease assays in P. falciparum apPOL

    PMID:24147857

    Open questions at the time
    • Fidelity measured in isolation without accessory replisome factors
    • Sequence-context dependence not mapped genome-wide
  6. 2013 Medium

    To identify replisome partners, PfSSB was shown to physically bind the PREX helicase domain and modulate its activity, placing PREX in a multi-protein context and mapping the interacting domains.

    Evidence Pulldown/co-IP interaction with PfSSB domain mapping and helicase modulation assay

    PMID:24267922

    Open questions at the time
    • Single-method interaction assay without reciprocal validation
    • Stoichiometry and in vivo relevance of PfSSB-PREX complex undefined
  7. 2014 Medium

    Beyond basic synthesis, PREX polymerase was shown to perform strand-displacement synthesis and this activity was leveraged into a high-throughput inhibitor screen, establishing PREX as a druggable antimalarial target.

    Evidence Fluorescent strand-displacement polymerase assay in 384-well format with a pilot compound screen

    PMID:24687154

    Open questions at the time
    • Hit compounds not validated for parasite killing or on-target action
    • Strand-displacement role in vivo not demonstrated
  8. 2016 High

    Providing the first structure, the 2.9 Å crystal structure of apPOL revealed divergence from typical A-family signature motifs and an N-terminal subdomain essential for exonuclease activity, and identified an inhibitor.

    Evidence X-ray crystallography, N-terminal subdomain truncation with exonuclease assay, and inhibitor testing

    PMID:27487482

    Open questions at the time
    • Structure solved without DNA or nucleotide bound
    • Inhibitor binding mode not directly observed
  9. 2020 High

    Addressing genome-integrity maintenance, PREX polymerase was shown to misincorporate oxidized 8oxodGTP and then remove it via proofreading, explaining how the AT-rich apicoplast genome is protected from oxidative mutagenesis.

    Evidence In vitro 8oxodGTP misincorporation and proofreading-excision assays

    PMID:32636411

    Open questions at the time
    • In vivo oxidative-damage protection not tested
    • Efficiency relative to other repair pathways unknown
  10. 2022 High

    Extending damage tolerance, PREX polymerase was shown to bypass three oxidative lesions using the unique fingers residues N505/Y509, identified by mutagenesis, defining a translesion capacity built into the replicative polymerase.

    Evidence In vitro translesion synthesis with lesion templates and site-directed mutagenesis of N505/Y509

    PMID:35220686

    Open questions at the time
    • Bypass fidelity/mutagenic outcome per lesion not fully quantified in vivo
    • Whether translesion synthesis is regulated or gated is unknown
  11. 2022 High

    Quantifying replication efficiency, transient-state kinetics revealed low processivity and error-prone lesion bypass, indicating PREX requires accessory or processivity factors for faithful genome replication.

    Evidence Pre-steady-state kinetics on undamaged and damaged templates

    PMID:36251801

    Open questions at the time
    • Identity of the inferred processivity factor not established
    • Reconstitution with candidate accessory factors not performed
  12. 2022 Medium

    Advancing drug discovery, SAR studies of the apPOL inhibitor MMV666123 combined with crystal structures of WT and mutant enzyme defined inhibition motifs and a modeled binding site.

    Evidence X-ray crystallography of WT/mutant apPOL, kinetic inhibition, and medicinal-chemistry SAR

    PMID:36191407

    Open questions at the time
    • Inhibitor binding mode modeled, not seen in a co-crystal
    • Cellular potency and selectivity not resolved here
  13. 2024 Medium

    To identify a lagging-strand partner, PREX was shown to co-immunoprecipitate with a novel apicoplast flap endonuclease PfExo, implicating a multi-component replisome for Okazaki-fragment processing.

    Evidence Co-immunoprecipitation of PREX-PfExo and in vitro nuclease characterization of PfExo

    PMID:38888125

    Open questions at the time
    • Single Co-IP without reciprocal validation
    • Nuclease characterization is of PfExo, not PREX; functional cooperation not reconstituted
  14. 2024 High

    Delivering a mechanistic structural model, cryo-EM ternary complexes with DNA and incoming nucleotide revealed high-fidelity active-site residues, absence of processivity elements, and large fingers/thumb conformational changes plus candidate allosteric sites.

    Evidence Cryo-EM of apPOL-DNA-nucleotide ternary complex with conformational analysis

    PMID:39490679

    Open questions at the time
    • Structures of the primase and helicase domains still lacking
    • Full replisome architecture with PfSSB and PfExo not visualized

Open questions

Synthesis pass · forward-looking unresolved questions
  • How PREX's four catalytic activities are physically coordinated within an assembled apicoplast replisome, and the identity of the processivity factor required for efficient in vivo replication, remain unresolved.
  • No reconstituted multi-protein replisome
  • Processivity factor unidentified
  • No structure of full-length matured PREX or of the primase/helicase modules

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
PFEXO (APICOPLAST FLAP ENDONUCLEASE/EXONUCLEASE) — CO-IMMUNOPRECIPITATES WITH PREX, IMPLICATED IN LAGGING-STRAND PROCESSING [#12]PFSSB (SINGLE-STRANDED DNA-BINDING PROTEIN) — INTERACTS WITH PREX HELICASE DOMAIN AND MODULATES HELICASE ACTIVITY [#5]

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 PREX (PF3D7_1411400) encodes a multi-domain polypeptide with demonstrated DNA primase, DNA helicase, DNA polymerase, and 3'-5' exonuclease activities. The primase/helicase domain is phylogenetically related to T7 bacteriophage gene 4 product and mammalian mitochondrial helicase Twinkle, while the polymerase domain belongs to the family A bacterial polymerases. The DNA polymerase activity is optimally active at 75°C. The N-terminal sequence of PREX directs a GFP reporter specifically to the P. falciparum apicoplast and not to the mitochondrion. PREX is the first example of a gene encoding contiguous DNA polymerase, DNA primase, and DNA helicase components. Biochemical activity assays (primase, helicase, polymerase, exonuclease), phylogenetic analysis, GFP reporter localization to apicoplast Molecular and biochemical parasitology High 15926203
2009 PREX has an orthologue in Toxoplasma gondii (TgPREX) with a bipartite apicoplast targeting sequence similar to that of PfPREX, capable of delivering marker proteins to the apicoplast. Bacterial expression of the T. gondii polymerase domain confirmed it to be enzymatically active. No PREX orthologue is detected in Cryptosporidium (which lacks a plastid), indicating PREX is conserved across plastid-bearing apicomplexans. Bioinformatic identification of orthologue, in silico targeting sequence analysis, bacterial expression and enzymatic activity assay of polymerase domain Parasitology Medium 19402939
2011 The minimal primase domain of PREX contains functional zinc-binding and TOPRIM-fold domains that are sufficient, in recombinant form, to produce RNA primers from a single-stranded DNA template. PREX undergoes extensive proteolytic maturation within the parasite, effectively separating its functional domains. Overexpression of PREX's trafficking and primase sequences in P. falciparum yields specific and dynamic localization to foci within the apicoplast. Attempts to knock out the Plasmodium yoelii orthologue of Prex were unsuccessful, indicating apparent essentiality of this protein. Recombinant domain expression and in vitro primase assay, proteolytic maturation analysis, GFP overexpression and live imaging in P. falciparum, gene-targeting knockout attempts in P. yoelii Molecular and biochemical parasitology High 21856338
2011 The DNA polymerase domain of PREX (referred to as KPom1) has a strongly biased mutational spectrum in which T→C is the most frequent single-base substitution, differing significantly from E. coli DNA Pol I. KPom1 lacking 3'→5' exonuclease activity was used to measure kinetic parameters for correct and incorrect nucleotide incorporation. KPom1 can complement an E. coli temperature-sensitive Pol I mutant at elevated temperature, demonstrating functional conservation of polymerase activity. LacZ-based forward mutation fidelity assay, kinetic nucleotide incorporation assays, E. coli Pol I temperature-sensitive complementation Journal of molecular biology High 21570407
2013 The apicoplast DNA polymerase domain of PREX (apPOL) exhibits differential nucleotide misincorporation probabilities (>50-fold variation across 12 misincorporations). Mismatch extension is the most dominant fidelity selection step (>350-fold variation). The 3'→5' proofreading exonuclease activity varies <3-fold across the 12 mismatches. Overall mutation frequency is highly dependent on both intrinsic polymerase fidelity and the identity of the template surrounding the mismatch. In vitro kinetic fidelity assays measuring misincorporation, mismatch extension, and exonuclease proofreading rates for all 12 possible mismatch combinations Biochemistry High 24147857
2013 P. falciparum single-stranded DNA-binding protein (PfSSB) physically interacts with the PREX helicase domain and modulates its helicase activity. The N-terminal domain of PfSSB mediates the interaction, while the C-terminal domain of PfSSB plays a pivotal role in modulating PREX helicase activity. Protein-protein interaction assay (pulldown/co-IP), domain mapping of PfSSB, helicase activity modulation assay FEMS microbiology letters Medium 24267922
2014 The apicoplast DNA polymerase domain of PREX (referred to as POM1) is capable of strand-displacement synthesis through a DNA hairpin substrate, a property exploited to develop a fluorescent high-throughput inhibitor screen. A pilot screen identified 62 compounds causing >50% inhibition, validating PREX apPOL as a druggable target. Fluorescent strand-displacement DNA polymerase assay in 384-well format; Z'-factor validation; pilot compound library screen Journal of biomolecular screening Medium 24687154
2016 Crystal structure of the apicoplast DNA polymerase domain of PREX (apPOL) resolved at 2.9 Å. The structure reveals apPOL diverges from typical A-family polymerases in two of three previously identified signature motifs and in an additional region. apPOL has an N-terminal subdomain whose absence severely diminishes 3'→5' exonuclease activity. A compound toxic to Plasmodium is a potent inhibitor of apPOL in vitro. X-ray crystallography at 2.9 Å; truncation mutagenesis of N-terminal subdomain with exonuclease activity assay; inhibitor biochemical assay Journal of molecular biology High 27487482
2020 The DNA polymerase module of PREX (PfpPol) can misincorporate the oxidized nucleotide 8oxodGTP opposite dA, introducing transversion mutations. The 3'→5' proofreading activity of PfpPol has the unique ability to remove the misincorporated oxidized nucleotide from the primer terminus, preventing mutagenesis of the AT-rich apicoplast genome. In vitro misincorporation assay with 8oxodGTP; in vitro proofreading excision assay at primer terminus Scientific reports High 32636411
2022 The DNA polymerase domain of PREX (PfpPol) is capable of translesion DNA synthesis past three common oxidative stress-induced DNA lesions: 2-hydroxydeoxyadenine, thymine glycol, and 8-oxodeoxyguanine. Residues N505 and Y509 in the fingers subdomain, which are unique to PfpPol among A-family polymerases, are required for bypass of all three lesions, as demonstrated by mutagenesis. In vitro translesion synthesis assay with defined lesion-containing templates; site-directed mutagenesis of N505 and Y509 with functional activity assays The FEBS journal High 35220686
2022 Transient-state kinetic analysis of the apicoplast DNA polymerase domain of PREX (apPol) reveals low processivity and low efficiency when copying undamaged DNA. apPol can bypass oxidatively damaged lesions but the bypass is error-prone. These properties suggest that accessory factors or a processivity factor are needed for faithful and efficient apicoplast genome replication. Transient-state pre-steady-state kinetics; processivity and fidelity assays on undamaged and damaged DNA templates Biochemistry High 36251801
2022 Structure-activity relationship studies of the apPOL inhibitor MMV666123 identify key structural motifs required for inhibition. Crystal structures of wild-type and mutant apo-apPOL facilitated model building of a putative inhibitor binding site. Kinetic analysis further characterized inhibitor binding, validating apPOL as a drug target. X-ray crystallography of WT and mutant apPOL; kinetic inhibition assays; SAR medicinal chemistry European journal of medicinal chemistry Medium 36191407
2024 PREX physically interacts with a novel apicoplast-targeted flap endonuclease/exonuclease (PfExo), which processes 5'-flaps, acts as a 5'→3' exonuclease on dsDNA, and functions as a bipolar nuclease on ssDNA and RNA-DNA hybrids. This interaction was detected by co-immunoprecipitation, suggesting PfExo participates in lagging strand processing during PREX-mediated apicoplast DNA replication. Co-immunoprecipitation detecting PREX–PfExo interaction; in vitro nuclease activity assays with multiple substrate types Nucleic acids research Medium 38888125
2024 Cryo-EM structures of PREX apPOL were determined in complex with DNA and incoming nucleotide. The structures reveal critical residues for high-fidelity DNA synthesis, absence of structural elements typically required for processive synthesis (consistent with need for accessory factors), and large-scale conformational changes upon DNA and nucleotide binding in the fingers and thumb subdomains. Potential allosteric sites were identified. Cryo-electron microscopy structure determination of apPOL–DNA–nucleotide ternary complex; structural comparison and conformational analysis Journal of molecular biology High 39490679

Source papers

Stage 0 corpus · 14 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 The plastidic DNA replication enzyme complex of Plasmodium falciparum. Molecular and biochemical parasitology 68 15926203
2011 The primase domain of PfPrex is a proteolytically matured, essential enzyme of the apicoplast. Molecular and biochemical parasitology 21 21856338
2013 Fidelity, mismatch extension, and proofreading activity of the Plasmodium falciparum apicoplast DNA polymerase. Biochemistry 17 24147857
2016 Crystal Structure of the Apicoplast DNA Polymerase from Plasmodium falciparum: The First Look at a Plastidic A-Family DNA Polymerase. Journal of molecular biology 13 27487482
2014 A High-Throughput Assay to Identify Inhibitors of the Apicoplast DNA Polymerase from Plasmodium falciparum. Journal of biomolecular screening 11 24687154
2011 The biochemistry and fidelity of synthesis by the apicoplast genome replication DNA polymerase Pfprex from the malaria parasite Plasmodium falciparum. Journal of molecular biology 11 21570407
2009 The Toxoplasma gondii plastid replication and repair enzyme complex, PREX. Parasitology 11 19402939
2022 Promising antimalarials targeting apicoplast DNA polymerase from Plasmodium falciparum. European journal of medicinal chemistry 8 36191407
2022 Pfprex from Plasmodium falciparum can bypass oxidative stress-induced DNA lesions. The FEBS journal 6 35220686
2020 The proofreading activity of Pfprex from Plasmodium falciparum can prevent mutagenesis of the apicoplast genome by oxidized nucleotides. Scientific reports 6 32636411
2013 Plasmodium falciparum single-stranded DNA-binding protein (PfSSB) interacts with PfPrex helicase and modulates its activity. FEMS microbiology letters 6 24267922
2022 Transient State Kinetics of Plasmodium falciparum Apicoplast DNA Polymerase Suggests the Involvement of Accessory Factors for Efficient and Accurate DNA Synthesis. Biochemistry 5 36251801
2024 A Plasmodium apicoplast-targeted unique exonuclease/FEN exhibits interspecies functional differences attributable to an insertion that alters DNA-binding. Nucleic acids research 3 38888125
2024 Cryo-EM Structures of the Plasmodium falciparum Apicoplast DNA Polymerase. Journal of molecular biology 3 39490679