Affinage · Toxoplasma gondii

PLP1

perforin-like protein PLP1 · UniProt V5BCL0

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

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TgPLP1 is a microneme-secreted perforin-like protein that permeabilizes membranes to drive rapid egress of Toxoplasma gondii from host cells and is a major determinant of acute virulence (PMID:19095897). It acts through a conserved perforin mechanism: PLP1 binds target membranes and oligomerizes into large multimeric membrane-embedded complexes, with both the central MACPF domain and the β-sheet-rich C-terminal domain required for lytic activity (PMID:23376275). Structurally, the MACPF domain assembles into hexameric ring and helical forms, while the C-terminal APCβ domain adopts a novel double-layered β-prism fold that anchors the protein to membranes via a hydrophobic loop tipped by a tryptophan; mutation of this loop abolishes egress as severely as deletion of PLP1 itself, and the domain binds preferentially to phosphatidylethanolamine-containing membranes (PMID:29750191, PMID:30513119). PLP1 activity is gated by pH: vacuolar acidification prior to and during egress—potentiated in the RH strain by FNT1/FNT2-mediated lactate and pyruvate excretion—promotes membrane binding and cytolysis, permeabilizing the parasitophorous vacuole membrane and then the host plasma membrane (PMID:25375818, PMID:35512005). The microneme protein MIC11 is required for PLP1-mediated membrane rupture and physically or functionally associates with PLP1, and its merozoite-specific paralogue MIC22 can substitute for it (PMID:41935076). Beyond driving escape, PLP1 shapes the host response, promoting a dysregulated, neutrophil-dominated lethal cytokine response during acute infection (PMID:40166190).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2008 High

    Established that a parasite-encoded perforin-like protein, not host factors alone, mediates membrane permeabilization during egress and is required for acute virulence.

    Evidence Genetic knockout with egress/permeabilization assays and mouse virulence model

    PMID:19095897

    Open questions at the time
    • Mechanism of membrane disruption (oligomerization, pore formation) not resolved
    • Domains responsible for activity not mapped
  2. 2013 High

    Showed PLP1 is sufficient for membrane disruption and acts by a conserved perforin mechanism, defining which domains carry lytic and membrane-binding activity.

    Evidence Domain-deletion complementation of the knockout with membrane lysis, egress, and virulence readouts

    PMID:23376275

    Open questions at the time
    • Atomic-resolution structure of the domains not available
    • Lipid specificity of membrane binding unknown
  3. 2014 High

    Identified pH as the trigger gating PLP1 activity, explaining how lytic activity is restrained during invasion but activated during egress.

    Evidence pH manipulation with membrane-binding, cytolysis, and egress assays using Δplp1 controls

    PMID:25375818

    Open questions at the time
    • Source of the pH change in the vacuole not identified
    • Molecular basis of pH sensing by PLP1 unknown
  4. 2018 High

    Provided the structural basis for pore assembly and membrane anchoring, defining the MACPF oligomeric assemblies and the APCβ β-prism fold with its phosphatidylethanolamine-selective hydrophobic loop.

    Evidence X-ray crystallography, molecular dynamics, mutagenesis, tryptophan fluorescence, and CRISPR point mutants with liposome and egress assays

    PMID:29750191 PMID:30513119

    Open questions at the time
    • Full-length pore structure in a membrane not resolved
    • How pH regulates the conformational transition not shown
  5. 2022 High

    Linked vacuolar acidification mechanistically to PLP1, showing FNT-mediated organic-acid excretion drives the PV pH drop that potentiates PLP1 during egress.

    Evidence Ratiometric pHluorin imaging, auxin-inducible FNT knockdown/knockout, metabolite release assays, and Δplp1 comparison in strain RH

    PMID:35512005

    Open questions at the time
    • Whether other acidifying pathways contribute not established
    • Findings shown in RH; strain generality untested
  6. 2026 High

    Identified MIC11 as a required co-factor for PLP1-mediated membrane rupture, revealing that PLP1 lysis depends on partner microneme proteins.

    Evidence CRISPR in vivo screen, MIC11 deletion, scanning mutagenesis, membrane-rupture and egress assays, and MIC22 complementation

    PMID:41935076

    Open questions at the time
    • Nature of the MIC11–PLP1 association (direct binding vs. functional) not fully resolved
    • Molecular step at which MIC11 acts unknown
  7. 2025 Medium

    Demonstrated PLP1 shapes host immunity, driving a dysregulated lethal cytokine response rather than merely enabling parasite escape.

    Evidence In vivo bioluminescence imaging, histology, flow cytometry, and cytokine profiling comparing Δplp1 and wild-type strain RH in mice (preprint)

    PMID:40166190

    Open questions at the time
    • Preprint, single lab, not independently replicated
    • Mechanism linking membrane lysis to cytokine dysregulation not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How pH-triggered conformational changes convert monomeric PLP1 into a membrane-inserted pore, and the precise molecular role of MIC11 in this transition, remain unresolved.
  • No membrane-embedded full-length pore structure
  • Order and coordination of PVM vs. host plasma membrane permeabilization at the molecular level unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
FNT1/FNT2 (FORMATE-NITRITE TRANSPORTERS POTENTIATING PLP1 VIA VACUOLAR ACIDIFICATION) [#5]MIC11 (MICRONEME PROTEIN REQUIRED FOR PLP1-MEDIATED MEMBRANE RUPTURE) [#7]MIC22 (MEROZOITE-SPECIFIC PARALOGUE THAT COMPLEMENTS MIC11) [#7]
Complex memberships
PLP1 MACPF hexameric ring / helical oligomeric assemblies [#3]PLP1–MIC11 functional/physical association [#7]

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 TgPLP1 is a secreted perforin-like protein required for rapid parasite egress from host cells; TgPLP1-deficient parasites fail to permeabilize the parasitophorous vacuole membrane (PVM) and host plasma membrane during exit, resulting in entrapment within host cells and a >5 order-of-magnitude reduction in acute virulence in mice. Genetic knockout (TgPLP1-deficient parasites), intracellular growth and egress assays, mouse virulence model Science High 19095897
2013 PLP1 is sufficient for membrane disruption and acts through a conserved perforin mechanism: it binds target membranes and oligomerizes to form large, multimeric membrane-embedded complexes. Both the central MACPF domain and the β-sheet-rich C-terminal domain are required for lytic activity. The N-terminal extension contributes to lytic activity and rapid egress but is not essential for virulence. Both N- and C-terminal domains possess membrane-binding activity, with the C-terminal domain being critical. Genetic complementation of PLP1 knockout with domain deletion constructs, membrane permeabilization assays, egress assays, mouse virulence model The Journal of Biological Chemistry High 23376275
2014 Acidification promotes membrane binding and cytolytic activity of PLP1; agents that neutralize pH reduce the efficiency of PLP1-dependent perforation of host membranes and compromise egress. Low extracellular pH also causes PLP1-dependent damage to host cells during microneme secretion, whereas neutral extracellular pH subdues PLP1 activity to allow cell invasion without overt host-cell damage. pH manipulation experiments, membrane binding assays, cytolytic activity assays, egress assays with pH-neutralizing agents, PLP1 knockout comparison PLoS Pathogens High 25375818
2018 Crystal structures of the TgPLP1 MACPF and APCβ (C-terminal) domains were solved. The MACPF domain forms hexameric ring and helical assemblies. The APCβ domain adopts a novel β-prism fold. Molecular dynamics simulations and site-directed mutagenesis in a liposome-based assay show that the APCβ domain binds preferentially to phosphatidylethanolamine membranes via a hydrophobic loop, enhanced by inositol phosphate lipids. X-ray crystallography, molecular dynamics simulations, site-directed mutagenesis, liposome-based membrane binding assay Science Advances High 29750191
2018 The TgPLP1 C-terminal APCβ domain crystal structure reveals an unusual double-layered β-prism fold with three direct-repeat subdomains. One subdomain features a protruding hydrophobic loop with a tip tryptophan; tryptophan fluorescence measurements indicate loop insertion into target membranes. CRISPR/Cas9-generated parasite strains with hydrophobic loop mutations (including alanine substitution of the tip tryptophan) are as deficient in egress as Δplp1 strains, establishing this loop as essential for membrane anchoring and cytolytic egress function. X-ray crystallography (high-resolution CTD structure), intrinsic tryptophan fluorescence spectrophotometry, CRISPR/Cas9 mutagenesis, egress assays, lipid-binding assays PLoS Pathogens High 30513119
2022 The parasitophorous vacuole (PV) pH drops significantly prior to and during egress; this pH drop is dependent on the presence of PLP1 or parasite motility (chemically paralyzed Δplp1 parasites show no pH drop, whereas paralyzed wild-type RH parasites do). Two formate-nitrite transporters (FNT1 and FNT2) contribute to vacuolar acidification by excreting lactate and pyruvate, thereby potentiating PLP1 activity during egress. Ratiometric pHluorin live-imaging pH measurement, auxin-induced conditional knockdown and knockout of FNTs, lactate/pyruvate release assays, chemical paralysis (motility inhibition), egress assays PLoS Pathogens High 35512005
2015 TgPLP1 is expressed in bradyzoites (not only tachyzoites) and localizes to micronemes in both stages; its transcript level decreases over time during in vitro differentiation into bradyzoites. Immunofluorescence assay (IFA), immunohistochemistry (IHC), quantitative PCR during stage differentiation Experimental Parasitology Medium 25746893
2026 The secretory microneme protein MIC11 is required for PLP1-mediated membrane disruption and egress; deletion of MIC11 causes severe defects in membrane rupture and egress. Mechanistic analyses support a physical or functional association between MIC11 and PLP1, suggesting MIC11 is involved in PLP1-dependent membrane disruption. Scanning mutagenesis identified functional motifs in MIC11. The merozoite-specific paralogue MIC22 functionally complements MIC11 deletion, suggesting a conserved egress mechanism. CRISPR-based in vivo screen, MIC11 deletion (KO), scanning mutagenesis, membrane rupture assays, egress assays, functional complementation with MIC22 Nature Communications High 41935076
2025 PLP1 promotes a lethal cytokine release syndrome during acute murine infection with virulent T. gondii. Δplp1 parasites disseminate but evoke a protective inflammatory response characterized by earlier myeloid cell activation, moderate neutrophil response, regulated induction of IFN-γ and TNF-α, and earlier IL-10 regulatory response, in contrast to the dysregulated, neutrophil-dominated, lethal response triggered by wild-type PLP1-expressing parasites. In vivo bioluminescence imaging, histological tissue analysis, flow cytometric analysis of immune cells, cytokine measurements, Δplp1 vs. wild-type comparison in mice bioRxiv (preprint)preprint Medium 40166190

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2008 Rapid membrane disruption by a perforin-like protein facilitates parasite exit from host cells. Science (New York, N.Y.) 232 19095897
2014 Acidification Activates Toxoplasma gondii Motility and Egress by Enhancing Protein Secretion and Cytolytic Activity. PLoS pathogens 55 25375818
2013 Functional dissection of Toxoplasma gondii perforin-like protein 1 reveals a dual domain mode of membrane binding for cytolysis and parasite egress. The Journal of biological chemistry 48 23376275
2009 New roles for perforins and proteases in apicomplexan egress. Cellular microbiology 48 19614666
2012 Vaccination with a DNA vaccine coding for perforin-like protein 1 and MIC6 induces significant protective immunity against Toxoplasma gondii. Clinical and vaccine immunology : CVI 33 22379063
2018 Structures of monomeric and oligomeric forms of the Toxoplasma gondii perforin-like protein 1. Science advances 28 29750191
2011 Toxoplasma gondii: protective immunity against experimental toxoplasmosis induced by a DNA vaccine encoding the perforin-like protein 1. Experimental parasitology 28 21310148
2019 A systematic review on efficiency of microneme proteins to induce protective immunity against Toxoplasma gondii. European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology 24 30680553
2018 Immuno-efficacy of DNA vaccines encoding PLP1 and ROP18 against experimental Toxoplasma gondii infection in mice. Experimental parasitology 16 29626423
2018 Structural basis of Toxoplasma gondii perforin-like protein 1 membrane interaction and activity during egress. PLoS pathogens 13 30513119
2010 Development of a screen to dissect Toxoplasma gondii egress. Molecular and biochemical parasitology 11 20227445
2022 Toxoplasma gondii excretion of glycolytic products is associated with acidification of the parasitophorous vacuole during parasite egress. PLoS pathogens 10 35512005
2015 Identification and co-localization of perforin-like (TgPLP1) protein in Toxoplasma gondii bradyzoites. Experimental parasitology 2 25746893
2025 Evaluation of Toxoplasma gondii Perforin-like Proteins (PLPs) to Find the Potential Epitopes for Immunization through in silico Approach. Recent advances in inflammation & allergy drug discovery 1 39901670
2026 An in vivo fitness gene of Toxoplasma, MIC11, is essential for PLP1-mediated egress from host cells. Nature communications 0 41935076
2026 Functional characterization of 11 novel rhoptry proteins in the type I RH strain of Toxoplasma gondii using the CRISPR-Cas9 system. Parasites & vectors 0 41975467
2025 Toxoplasma induced cytokine release syndrome is critically dependent on the expression of pore-forming Perforin-Like Protein-1. bioRxiv : the preprint server for biology 0 40166190