Affinage · Plasmodium

PF3D7_0203900

5'-3' exonuclease, putative

Annotated
2026-09-07
1 papers in source corpus 1 papers cited in narrative 5 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PF3D7_0203900 (PfExo) is an apicoplast-targeted 5'-3' exonuclease/flap endonuclease that functions within the apicoplast DNA replication machinery of Plasmodium falciparum (PMID:38888125). It contains a [4Fe-4S] cluster and a long low-complexity region (LCR) insertion, and displays broad nucleolytic activity in vitro—hydrolyzing 5'-flaps, processing dsDNA as a 5'-3' exonuclease, and acting as a bipolar nuclease on ssDNA and RNA-DNA hybrids (PMID:38888125). The LCR insertion is the direct determinant of this broad substrate range: its deletion compromises DNA binding and narrows the substrate repertoire, while transplanting it into the naturally insertion-lacking P. berghei ortholog (PbExo) confers new activities (PMID:38888125). PfExo physically associates with the apicoplast multifunctional DNA polymerase PfPrex, positioning it as a candidate flap endonuclease and RNaseH for apicoplast genome replication (PMID:38888125), and knockout of the PbExo ortholog establishes that the enzyme is essential for parasite survival (PMID:38888125). Beyond these findings, no further mechanistic detail has been characterized in the available corpus.

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2024 High

    Whether PF3D7_0203900 possessed catalytic nuclease activity and on which substrates was unknown; in vitro reconstitution defined it as a broad-spectrum 5'-3' exonuclease/FEN, establishing its biochemical repertoire.

    Evidence In vitro enzymatic assays on 5'-flap, dsDNA, ssDNA, and RNA-DNA hybrid substrates using purified P. falciparum PfExo

    PMID:38888125

    Open questions at the time
    • No structural model of the catalytic site or [4Fe-4S] cluster is reported
    • The physiological substrate(s) during replication are inferred from in vitro range, not directly demonstrated in vivo
  2. 2024 High

    It was unclear what molecular feature accounted for PfExo's unusually broad substrate range; gain- and loss-of-function mutagenesis identified the LCR insertion as the direct determinant of substrate breadth and DNA binding.

    Evidence Deletion mutagenesis (PfExoΔins) and domain-swap into PbExo, with in vitro enzymatic and DNA-binding assays comparing P. falciparum and P. berghei enzymes

    PMID:38888125

    Open questions at the time
    • The structural mechanism by which the LCR insertion enhances DNA binding is not resolved
    • Whether insertion-dependent activities are used in vivo is untested
  3. 2024 Medium

    Whether PfExo operates within the apicoplast replication apparatus was unknown; detection of an interaction with the polymerase PfPrex placed it in the apicoplast DNA replication machinery.

    Evidence Co-immunoprecipitation / interaction detection between PfExo and PfPrex in P. falciparum

    PMID:38888125

    Open questions at the time
    • Single reported interaction detection without reciprocal confirmation described
    • The stoichiometry, interface, and functional consequence of the PfExo–PfPrex interaction are undefined
  4. 2024 Medium

    Whether this exonuclease is required in vivo was unknown; knockout of the P. berghei ortholog demonstrated essentiality for parasite survival.

    Evidence Genetic knockout of PbExo in P. berghei with a parasite viability readout

    PMID:38888125

    Open questions at the time
    • Essentiality shown via the P. berghei ortholog rather than PF3D7_0203900 directly
    • The specific replication defect underlying loss of viability is not defined
  5. 2024 Medium

    PfExo was localized to the apicoplast, consistent with a role in apicoplast genome replication and maintenance.

    Evidence Apicoplast targeting/localization described within the functional study in P. falciparum

    PMID:38888125

    Open questions at the time
    • Localization method details are not fully specified
    • Sub-apicoplast distribution and colocalization with replication foci are not shown

Open questions

Synthesis pass · forward-looking unresolved questions
  • Whether PfExo acts as the definitive flap endonuclease and/or RNaseH during apicoplast DNA replication, and how its activities are coordinated with PfPrex in vivo, remains open.
  • No in vivo demonstration of flap endonuclease or RNaseH function during plDNA replication
  • No structural characterization of the enzyme or the PfExo–PfPrex complex
  • Direct genetic disruption of PF3D7_0203900 in P. falciparum not reported

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
PFPREX (APICOPLAST MULTIFUNCTIONAL DNA POLYMERASE) [#2]
Complex memberships
PfExo–PfPrex apicoplast DNA replication assembly [#2]

Evidence

Reading pass · 5 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2024 PF3D7_0203900 (PfExo) is an apicoplast-targeted 5'-3' exonuclease/FEN containing a [4Fe-4S] cluster and a long low-complexity region (LCR) insertion; it exhibits a broad substrate range, hydrolyzing 5'-flaps, processing dsDNA as a 5'-3' exonuclease, and acting as a bipolar nuclease on ssDNA and RNA-DNA hybrids. In vitro enzymatic assays on multiple DNA/RNA substrates (5'-flap, dsDNA, ssDNA, RNA-DNA hybrids) Nucleic Acids Research High 38888125
2024 The LCR insertion in PfExo is required for broad substrate recognition; deletion of the insertion (PfExoΔins) compromised DNA binding and restricted the substrate repertoire to resemble the P. berghei ortholog (PbExo), which naturally lacks the insertion. Conversely, introducing the PfExo insertion into PbExo conferred activities the latter initially lacked, demonstrating the insertion directly expands substrate range. Deletion mutagenesis (PfExoΔins) and domain-swap mutagenesis (insertion introduced into PbExo), followed by in vitro enzymatic assays and DNA-binding analysis Nucleic Acids Research High 38888125
2024 PfExo physically interacts with PfPrex, the apicoplast multifunctional DNA polymerase, placing PfExo in the apicoplast DNA replication machinery. Co-immunoprecipitation / interaction detection (interaction with PfPrex detected) Nucleic Acids Research Medium 38888125
2024 Knockout of the P. berghei ortholog PbExo demonstrated essentiality of this enzyme for parasite survival, indicating the exonuclease function is required in vivo. Genetic knockout in P. berghei with parasite viability readout Nucleic Acids Research Medium 38888125
2024 PfExo localizes to the apicoplast, consistent with its role in apicoplast genome (plDNA) replication and maintenance. Apicoplast targeting predicted and consistent with experimental fractionation/localization data implied by apicoplast-targeted annotation and functional context Nucleic Acids Research Medium 38888125

Source papers

Stage 0 corpus · 1 paper · ranked by NIH iCite citations
Year Title Journal Citations PMID
2024 A Plasmodium apicoplast-targeted unique exonuclease/FEN exhibits interspecies functional differences attributable to an insertion that alters DNA-binding. Nucleic acids research 2 38888125