Affinage · Plasmodium

PFN

PF3D7_0932200 · profilin

Annotated
2026-09-08
15 papers in source corpus 9 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PF3D7_0932200 (PFN) is an essential actin-regulatory protein of malaria parasites that governs actin dynamics underlying invasive-stage motility (PMID:19000816, PMID:23245327). It sequesters actin monomers to inhibit spontaneous polymerization, yet at equimolar ratios does not compete with the actin-nucleating activity of formin 1, allowing controlled filament assembly (PMID:22428073). Structurally, PFN carries an apicomplexan-specific minidomain — a large beta-hairpin extension plus a Plasmodium-specific acidic loop — and folds as two independent units whose distinct halves segregate binding sites for different ligands (PMID:19000816, PMID:26012696). The beta-hairpin motif forms a unique PFN–actin interface that is critical for actin binding and fine-tunes gliding-motility speed of P. berghei sporozoites (PMID:28552953); beyond actin sequestration, PFN also contributes to force generation during sporozoite migration through a function that is independent of its actin-binding activity, since non-actin-binding mutants still reduce force and increase retrograde flow (PMID:32034083). Overexpression in P. berghei sporozoites specifically disrupts circular gliding, salivary gland invasion, and tip actin accumulation, underscoring stage-specific dosage sensitivity (PMID:27226484). PFN is proteolysed in vitro by the subtilisin-like protease PfSUB3 (PMID:24080030), and its interaction with actin-1 is the target of the antimalarial compound MMV020291, whose analogues disrupt filamentous actin formation and whose resistance mutations map to PFN and actin-1 (PMID:37053271).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2008 High

    Establishing that PFN adopts a distinctive apicomplexan-specific fold and is genetically required answered whether it is a viable, parasite-selective target rather than a generic profilin.

    Evidence X-ray crystallography of PFN alone and with a polyproline peptide plus P. berghei reverse-genetics knockout

    PMID:19000816

    Open questions at the time
    • Did not resolve the PFN-actin complex structure
    • Essentiality shown only for invasive blood stages
  2. 2012 Medium

    Biochemical reconstitution defined PFN's core activity as actin-monomer sequestration and showed it does not antagonize formin 1 nucleation, framing how PFN can both restrain and permit polymerization.

    Evidence In vitro actin polymerization assays with recombinant PFN and the formin 1 FH2 domain

    PMID:22428073

    Open questions at the time
    • Single in vitro method
    • Interplay quantified only at equimolar ratio
    • No cellular validation
  3. 2012 Medium

    Conditional knockdown confirmed PFN essentiality in blood stages with a defined loss-of-viability phenotype, moving beyond gene-disruption inference.

    Evidence TetR-aptamer conditional knockdown in P. berghei blood stages with viability assay

    PMID:23245327

    Open questions at the time
    • Molecular basis of lethality not dissected
    • Single lab/system
  4. 2013 Medium

    Identifying PFN as a PfSUB3 substrate and detecting proinflammatory cytokine induction raised the possibility of regulatory processing and immune interactions beyond its cytoskeletal role.

    Evidence In vitro protease assay (recombinant PfSUB3 + PFN); cytokine induction in mouse bone marrow-derived dendritic cells

    PMID:24080030

    Open questions at the time
    • No in vivo cleavage or mutagenesis of the cleavage site
    • Cytokine activity not linked to a parasite phenotype
  5. 2015 Medium

    Demonstrating that PFN is built from two independently folding units with segregated ligand-binding sites explained its architecture as an apparent ancient gene fusion and mapped functional halves.

    Evidence Domain-swapped mutagenesis and reassembly of half-profilin fragments with biophysical characterization

    PMID:26012696

    Open questions at the time
    • Physiological relevance of the fusion architecture untested in parasites
    • Specific ligands of each half not fully enumerated
  6. 2016 Medium

    Stage-specific overexpression revealed PFN dosage is critical selectively in sporozoites, linking PFN levels to gliding, salivary gland invasion, and tip actin organization.

    Evidence Transgenic stage-specific overexpression in P. berghei with gliding and invasion assays and tip actin imaging

    PMID:27226484

    Open questions at the time
    • Why sporozoites are uniquely sensitive unexplained
    • Overexpression is not a physiological perturbation
  7. 2017 High

    Mutating the apicomplexan-specific beta-hairpin established this motif as the actin-binding determinant that fine-tunes gliding speed, connecting a unique structural feature to motor mechanics.

    Evidence Beta-hairpin mutagenesis, sporozoite gliding assays, laser-tweezer force measurements, and molecular dynamics in P. berghei

    PMID:28552953

    Open questions at the time
    • Quantitative contribution of the acidic loop not isolated
    • Link to specific downstream motor components unresolved
  8. 2020 High

    Showing that non-actin-binding PFN mutants still reduce force and increase retrograde flow uncoupled PFN's force-generation role from its canonical actin-binding activity.

    Evidence Non-actin-binding PFN mutants tested by laser-tweezer force measurements on migrating P. berghei sporozoites plus in vitro binding assays

    PMID:32034083

    Open questions at the time
    • Molecular mechanism of the actin-binding-independent function unknown
    • Partner mediating force generation not identified
  9. 2023 High

    Mapping MMV020291 resistance to PFN and actin-1 and showing analogues disrupt F-actin formation in the presence of PFN validated the PFN–actin-1 interface as an antimalarial target.

    Evidence WGS of resistant lines, CRISPR-Cas9 mutation engineering, in vitro cosedimentation with recombinant PFN and actin-1, and apicoplast segregation assays in P. falciparum

    PMID:37053271

    Open questions at the time
    • Direct compound-PFN binding not structurally resolved
    • Whether PFN or actin-1 is the primary drug-contact site unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • The molecular basis of PFN's actin-binding-independent force-generation function and its structural interface with actin-1 during drug engagement remain unresolved.
  • No structure of the PFN-actin-1 complex
  • Physiological role of PfSUB3 cleavage of PFN unknown
  • Mechanism coupling PFN to force generation not defined

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
ACTIN-1 (PFACT1)FORMIN 1 (FH2 DOMAIN)PFSUB3 (SUBTILISIN-LIKE PROTEASE 3)

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 Crystal structure of P. falciparum PFN was solved alone and in complex with a polyproline ligand peptide, revealing a unique minidomain consisting of a large beta-hairpin extension common to all apicomplexan parasites and an acidic loop specific to Plasmodium species. Reverse genetics in P. berghei demonstrated PFN is essential for invasive blood stages. X-ray crystallography (crystal structure of PFN alone and with polyproline peptide); reverse genetics (P. berghei knockout) Structure High 19000816
2012 P. falciparum PFN alone sequesters actin monomers, thereby inhibiting polymerization; however, its monomer-sequestering activity does not compete with the nucleating activity of formin 1 at an equimolar profilin-actin ratio. In vitro actin polymerization assay with recombinant P. falciparum PFN and formin 1 FH2 domain PloS one Medium 22428073
2012 Tetracycline-induced conditional knockdown of P. berghei PFN using an ApiAP2-based transactivator system resulted in a dramatic reduction in parasite viability, establishing PFN as essential. Conditional knockdown (TetR-aptamer regulatable system) in P. berghei blood stages; viability assay Cell host & microbe Medium 23245327
2013 Mature P. falciparum subtilisin-like protease 3 (PfSUB3) proteolysed recombinant P. falciparum PFN in a dose-dependent manner in vitro, identifying PFN as a substrate of PfSUB3. Additionally, recombinant PFN was found to induce TNF-α and IL-12 production from mouse bone marrow-derived dendritic cells, indicating a proinflammatory activity. In vitro protease activity assay (recombinant PfSUB3 + recombinant PFN); cytokine induction assay with mouse dendritic cells Molecular and biochemical parasitology Medium 24080030
2015 P. falciparum PFN is a small globular protein that consists of two independently folding units (foldons), with binding sites for different protein ligands segregated in the two halves, suggesting evolution via an ancient gene fusion event. A domain-swapped mutant and half-profilins that can reassemble into full PFN were engineered to demonstrate this. Domain-swapped mutagenesis; expression of separate half-profilin fragments and reassembly assay; structural/biophysical characterization Cellular and molecular life sciences Medium 26012696
2016 Overexpression of P. berghei PFN in sporozoites (but not in merozoites or ookinetes) impaired circular gliding motility and salivary gland invasion, while strong overexpression caused complete life cycle arrest. Overexpression correlated with altered actin accumulation at the parasite tip. Transgenic overexpression with stage-specific promoters in P. berghei; gliding motility assays; fluorescence imaging of actin at parasite tip Molecular biology of the cell Medium 27226484
2017 The apicomplexan-specific beta-hairpin motif of PFN is critically involved in actin binding. Mutations in this motif impaired gliding motility of P. berghei sporozoites. Force measurements using laser tweezers on migrating sporozoites, combined with molecular dynamics simulations, showed that the unique PFN-actin interface fine-tunes gliding motility speed. Site-directed mutagenesis of PFN beta-hairpin; P. berghei sporozoite gliding motility assay; laser tweezer force measurements; molecular dynamics simulations PLoS pathogens High 28552953
2020 Mutations in PFN that do not affect actin binding in vitro still reduce force generation during P. berghei sporozoite migration and increase retrograde flow, demonstrating a function of PFN in force generation that is independent of its actin-binding activity. Site-directed mutagenesis of PFN (non-actin-binding mutants); laser tweezer force measurements on migrating P. berghei sporozoites; in vitro actin binding assays Journal of cell science High 32034083
2023 Resistance mutations in P. falciparum PFN (N154Y, K124N) and actin-1 (M356L) were identified after selection with compound MMV020291. CRISPR-Cas9 engineering of these mutations into wild-type parasites conferred resistance. In vitro cosedimentation assays with recombinant P. falciparum proteins showed that potent MMV020291 analogues disrupt filamentous actin formation in the presence of PFN, establishing PFN as part of the drug target mechanism. The compound also inhibited actin-1-dependent apicoplast segregation. Whole genome sequencing of resistant lines; CRISPR-Cas9 engineering of resistance mutations; in vitro actin cosedimentation assay with recombinant PFN and actin-1; apicoplast segregation assay PLoS biology High 37053271

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 A tetracycline-repressible transactivator system to study essential genes in malaria parasites. Cell host & microbe 76 23245327
2012 Mammalian and malaria parasite cyclase-associated proteins catalyze nucleotide exchange on G-actin through a conserved mechanism. The Journal of biological chemistry 54 23184938
2008 Structural basis for parasite-specific functions of the divergent profilin of Plasmodium falciparum. Structure (London, England : 1993) 53 19000816
2017 A unique profilin-actin interface is important for malaria parasite motility. PLoS pathogens 40 28552953
2019 The Liver-Stage Plasmodium Infection Is a Critical Checkpoint for Development of Experimental Cerebral Malaria. Frontiers in immunology 20 31736970
2013 Proteolytic activity of Plasmodium falciparum subtilisin-like protease 3 on parasite profilin, a multifunctional protein. Molecular and biochemical parasitology 19 24080030
2012 The lasso segment is required for functional dimerization of the Plasmodium formin 1 FH2 domain. PloS one 18 22428073
2023 Sulfonylpiperazine compounds prevent Plasmodium falciparum invasion of red blood cells through interference with actin-1/profilin dynamics. PLoS biology 17 37053271
2020 A function of profilin in force generation during malaria parasite motility that is independent of actin binding. Journal of cell science 13 32034083
2016 Comparative Plasmodium gene overexpression reveals distinct perturbation of sporozoite transmission by profilin. Molecular biology of the cell 7 27226484
2015 Two independently folding units of Plasmodium profilin suggest evolution via gene fusion. Cellular and molecular life sciences : CMLS 7 26012696
2020 Synthetic DNA Vaccines Adjuvanted with pIL-33 Drive Liver-Localized T Cells and Provide Protection from Plasmodium Challenge in a Mouse Model. Vaccines 4 31936739
2018 Potential role of salt-bridges in the hinge-like movement of apicomplexa specific β-hairpin of Plasmodium and Toxoplasma profilins: A molecular dynamics simulation study. Journal of cellular biochemistry 3 29236299
2026 Discovery of parasite proteins in the urine of vivax malaria patients through mass spectrometry. Diagnostic microbiology and infectious disease 1 41581407
2026 Biological activity of Juglans regia leaf extract and in silico evaluation of its phytochemicals against Plasmodium berghei target proteins. Helminthologia 0 42305886