Affinage · Plasmodium

PMX

PF3D7_0808200 · plasmepsin X

Annotated
2026-09-08
32 papers in source corpus 18 papers cited in narrative 18 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PMX (PF3D7_0808200) is an essential Plasmodium falciparum aspartic protease that acts as a master maturase governing the proteolytic cascade underlying merozoite egress from and invasion of erythrocytes (PMID:29074774, PMID:29074775, PMID:32109369). Functioning within acidic secretory organelles, PMX cleaves microneme and exoneme substrates prior to their discharge, while PMX-dependent rhoptry substrates are processed only after exoneme discharge into the parasitophorous vacuole (PMID:35927261). A central substrate is the subtilisin-like protease SUB1: PMX directly removes SUB1's inhibitory prodomain fragment p31, relieving propiece autoinhibition and activating SUB1, whereas the further conversion of the p54 intermediate to p47 is dispensable for activity (PMID:37036362). PMX also processes the N-terminal prodomain of PfRh5 within micronemes of the PCRCR complex, exposing its basigin-binding function required for invasion, establishing PMX as a hub coordinating both egress and invasion effectors (PMID:37072430). PMX activity is controlled upstream by the ER-resident calcium-binding protein PfERC, whose knockdown blocks proteolytic maturation of PMX and consequently SUB1 cleavage (PMID:32098818). Structurally, the PMX zymogen is held inactive by a unique twisted prosegment loop engaging Arg244, and maturation proceeds through prosegment cleavage; the catalytic aspartates D266 and D467 form the active site, and PMX recognizes an SFhE consensus motif favoring Phe at P1 (PMID:35048450, PMID:40043835, PMID:35906744). PMX is a validated antimalarial drug target: inhibitors including 49c, the dual PMIX/PMX inhibitor WM382, and a 2-piperazino-pyrimidine (FPSA) block its enzymatic and substrate-processing activity, with WM382 active across asexual blood, liver, and transmission stages, and resistance mapping to substitutions in the PMX locus (PMID:29074775, PMID:29074774, PMID:32109369, PMID:42025246).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2016 Medium

    Before its egress/invasion role was defined, it was unknown whether PMX is expressed and functional in mosquito stages; detection in gametes, zygotes and ookinetes with antibody-mediated blockade of midgut invasion established a transmission-stage role.

    Evidence RT-PCR, western blot, immunofluorescence, and standard membrane feeding assay in P. falciparum mosquito stages

    PMID:26911483

    Open questions at the time
    • No direct genetic knockout of PMX in mosquito stages
    • Substrates in gametes/zygotes/ookinetes not identified
  2. 2017 High

    The essential function of PMX in the blood stage was unknown; conditional genetics plus recombinant enzyme assays established PMX as an essential protease controlling SUB1 maturation and cleaving microneme egress/invasion factors.

    Evidence Conditional knockdown/gene excision and in vitro cleavage assays with recombinant PMX and inhibitor 49c, in two simultaneous P. falciparum studies

    PMID:29074774 PMID:29074775

    Open questions at the time
    • Full substrate repertoire not enumerated
    • Mechanism of PMX zymogen activation not resolved
  3. 2020 High

    How PMX itself is regulated was unknown; epistasis placed the ER-resident calcium-binding protein PfERC upstream of PMX maturation, linking PMX activation to secretory-organelle regulation.

    Evidence Conditional knockdown of PfERC and double-mutant immunoblot analysis of PMX and SUB1 processing in P. falciparum

    PMID:32098818

    Open questions at the time
    • Direct molecular mechanism by which PfERC controls PMX maturation not defined
    • Whether PfERC acts on PMX directly or via other factors unresolved
  4. 2020 High

    The breadth of PMX's role across the life cycle and its druggability were unknown; a dual PMIX/PMX inhibitor demonstrated PMX matures invasion, development and egress proteins and blocks asexual, liver and transmission stages.

    Evidence Chemical inhibition with WM382, in vivo P. berghei and humanized-mouse P. falciparum models, and in vitro resistance selection

    PMID:32109369

    Open questions at the time
    • Inhibitor targets both PMIX and PMX, so PMX-specific contributions per stage not fully separated
    • Individual stage-specific substrates not mapped
  5. 2022 High

    The structural basis for PMX zymogen inactivation and inhibitor binding was unknown; crystal structures revealed a novel prosegment twisted loop engaging Arg244 and defined the active-site inhibitor interactions.

    Evidence X-ray crystallography of PfPMX zymogen and inhibitor-bound forms with active-site mutant analysis

    PMID:35048450

    Open questions at the time
    • Structure of the fully mature enzyme with a physiological substrate not captured
    • Dynamics of activation in vivo not observed
  6. 2022 High

    Whether PMX autoprocessing and prodomain retention are required for function was unknown; a non-cleavable full-length mutant retained activity and normal trafficking, while the N-terminal prodomain half was shown necessary for trafficking, and the timing of substrate cleavage relative to discharge was defined.

    Evidence Site-directed cleavage-site mutagenesis, in vitro enzymatic assay, parasite transfection, localization and fractionation in P. falciparum

    PMID:35927261

    Open questions at the time
    • Functional significance of the multiple autoprocessed isoforms unclear
    • Trafficking receptor/machinery engaging the prodomain not identified
  7. 2022 Medium

    Determinants of PMX substrate specificity and selectivity versus PMIX were unknown; kinetic and structural profiling defined an SFhE consensus motif and mapped drug selectivity to the S' and S3 regions.

    Evidence X-ray crystallography of P. falciparum and P. vivax PMX with WM4/WM382, enzyme kinetics, peptidomimetic SAR and substrate profiling

    PMID:35460613 PMID:35906744

    Open questions at the time
    • Native protein substrate cleavage sites not all validated against the consensus
    • In-parasite specificity determinants not tested by mutagenesis
  8. 2023 High

    The precise mechanism of PMX-dependent SUB1 activation was unknown; direct cleavage of the p31 inhibitory prodomain (not the p54-to-p47 conversion) was shown to relieve propiece inhibition and activate SUB1.

    Evidence Recombinant protein cleavage assays with site mapping and PMX conditional knockdown/immunoblot in P. falciparum (peer-reviewed, preceded by bioRxiv preprint)

    PMID:36712005 PMID:37036362

    Open questions at the time
    • Kinetics of p31 removal in vivo not quantified
    • Whether other cofactors modulate this activation not addressed
  9. 2023 High

    Beyond SUB1, whether PMX activates invasion-complex ligands was unknown; PMX was shown to process the PfRh5 N-terminal prodomain within micronemes of the PCRCR complex to expose basigin binding.

    Evidence Biochemical PCRCR processing analysis, conditional PMX manipulation, mass spectrometry and invasion assays in P. falciparum

    PMID:37072430

    Open questions at the time
    • Kinetic ordering of PfRh5 versus SUB1 processing not defined
    • Other PCRCR component processing events not fully mapped
  10. 2024 Medium

    The physicochemical context of SUB1 prodomain inhibition and its relief was unclear; work showed p31 acts as a pH-dependent dimeric autoinhibitor cleaved by PMX in acidic organelles, with SUB1 fully activated upon neutral-pH discharge.

    Evidence Crystal structure of full-length PfSub1, recombinant protein activity and dimerization assays inferring PMX's acidic-organelle action in P. falciparum

    PMID:38386597 PMID:38969256

    Open questions at the time
    • PMX itself was not the direct experimental subject in the Sub1 structural work
    • Behavior of PMX under the same pH transitions not directly measured
  11. 2025 High

    High-resolution definition of the PMX active site engaging an inhibitor was lacking; a 1.7 Å structure revealed catalytic aspartates D266/D467 contacting the hydroxyethylamine pharmacophore and a novel closure conformation of the S2'/S2 loop and S2 flap.

    Evidence X-ray crystallography of PMX bound to macrocyclic peptidomimetic 7k with molecular docking

    PMID:40043835

    Open questions at the time
    • Conformational flexibility during catalysis of native substrates not resolved
    • Generalizability of the closure conformation to other inhibitor classes unknown
  12. 2026 High

    Whether new chemotypes engage PMX directly and how resistance arises was unknown; a 2-piperazino-pyrimidine (FPSA) was shown to inhibit recombinant PMX and block substrate processing, with resistance mapping to PMX-locus substitutions and duplications.

    Evidence Resistant-parasite selection with whole-genome sequencing, CRISPR editing, in vitro enzymatic assay and cellular substrate processing in P. falciparum Dd2

    PMID:42025246

    Open questions at the time
    • Structural basis of I252V/E55G-mediated resistance not resolved
    • Contribution of gene duplication versus point mutation to resistance not dissected

Open questions

Synthesis pass · forward-looking unresolved questions
  • The complete PMX substrate repertoire across all life-cycle stages and the direct molecular mechanism linking PfERC to PMX zymogen maturation remain undefined.
  • Full census of PMX substrates beyond SUB1 and PfRh5/PCRCR not established
  • Direct biochemical link between PfERC and PMX activation unresolved
  • Stage-specific mosquito-stage substrates uncharacterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
PFERC (ER-RESIDENT CALCIUM-BINDING PROTEIN; UPSTREAM REGULATOR OF PMX MATURATION) [#2]PFRH5 / PCRCR COMPLEX (SUBSTRATE — PRODOMAIN PROCESSING EXPOSES BASIGIN BINDING) [#8]SUB1 (SUBTILISIN-LIKE PROTEASE; SUBSTRATE — P31 PRODOMAIN REMOVAL ACTIVATES SUB1) [#0, #7, #10]
Complex memberships
PMX processes the PfRh5/PCRCR invasion complex (substrate, not a component) [#8]

Evidence

Reading pass · 18 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2017 PMX (PF3D7_0808200) is essential for both erythrocyte egress and invasion in P. falciparum, acting by controlling maturation of the subtilisin-like serine protease SUB1 in exoneme secretory vesicles. Conditional knockdown/genetic ablation combined with cell biological and biochemical analysis of SUB1 maturation Science High 29074774 29074775
2017 Recombinantly expressed PMX cleaves egress and invasion factors in a manner sensitive to the inhibitor compound 49c, establishing PMX as the maturase for microneme proteins including those required for egress. In vitro cleavage assay with recombinant PMX and PMX inhibitor 49c; conditional gene excision Science High 29074774 29074775
2020 PMX is required for the proteolytic maturation of SUB1 in P. falciparum; knockdown of the ER-resident calcium-binding protein PfERC prevents proteolytic maturation of PMX, which in turn prevents SUB1 cleavage, placing PfERC upstream of PMX in the egress proteolytic cascade. Conditional knockdown of PfERC; double-mutant parasite analysis; immunoblot analysis of PMX and SUB1 processing mBio High 32098818
2020 PMX acts as a master modulator of merozoite invasion by directly maturing proteins required for invasion, parasite development, and egress; dual PMX/PMIX inhibitor WM382 blocks multiple life-cycle stages including asexual blood stage, liver stage, and transmission to mosquitoes. Chemical inhibition with WM382 (dual PMIX/PMX inhibitor); in vivo mouse models (P. berghei and humanized mouse P. falciparum); in vitro selection for resistance Cell host & microbe High 32109369
2022 PMX autoprocesses via self-cleavage at multiple sites to generate different isoforms; a quadruple cleavage-site mutant that remains full-length retains in vitro enzymatic activity and is trafficked normally, supporting normal egress, invasion and parasite growth. The N-terminal half of the prodomain remains bound to the catalytic domain after processing and is required for proper intracellular trafficking of PMX. PMX cleaves microneme and exoneme substrates before their discharge, while rhoptry substrates dependent on PMX are cleaved after exoneme discharge into the parasitophorous vacuole. Site-directed mutagenesis of cleavage sites; in vitro enzymatic assay; parasite transfection; localization studies; biochemical fractionation Nature communications High 35927261
2022 Crystal structures of PfPMX zymogen reveal a novel inactivation mechanism involving a unique twisted loop from the prosegment and Arg244 from the mature enzyme. Maturation occurs through cleavage of the prosegment at multiple sites. The structure also provides molecular details of inhibitor 49c binding to the active site. X-ray crystallography of PfPMX zymogen and inhibitor-bound forms; active-site mutant analysis Protein science High 35048450
2022 Structures of PMX from P. falciparum and P. vivax bound to inhibitors WM4 and WM382 reveal that PMX and PMIX have similar substrate specificity but distinct differences for peptide and protein substrates; drug selectivity differences between PMIX and PMX map to variations in the S' region and engagement of the S3 pocket. X-ray crystallography; enzyme kinetic assays; substrate specificity profiling Structure High 35460613
2023 PMX directly cleaves both the inhibitory prodomain fragment p31 and the p54 intermediate of SUB1 in vitro using recombinant proteins. PMX cleavage of p31 removes the inhibitory propiece, activating SUB1; upon PMX knockdown, the p31-p54 complex accumulates in parasites. The conversion of p54 to p47 by PMX is not required for SUB1 activity once p31 is removed. Recombinant protein cleavage assay; mapping of cleavage sites; PMX conditional knockdown; immunoblot mBio High 37036362
2023 PMX processes the N-terminal prodomain of PfRh5 within micronemes of the PCRCR invasion complex, activating the complex to expose its basigin-binding function required for merozoite invasion of erythrocytes. Biochemical analysis of PCRCR complex processing; conditional PMX manipulation; invasion assays; mass spectrometry Nature communications High 37072430
2016 PMX protein is expressed in gametes, zygotes, and ookinetes of P. falciparum (mosquito stages), as confirmed by RT-PCR, western blot, and immunofluorescence; antibodies against PMX reduce P. falciparum invasion of the mosquito midgut. RT-PCR; western immunoblot; immunofluorescence assay; standard membrane feeding assay (SMFA) Malaria journal Medium 26911483
2024 PMX-mediated cleavage of the SUB1 prodomain (p31) activates SUB1 enzyme activity; p31 and the p31-p54 complex are largely dimeric under acidic conditions where PMX acts; PMX cleavage of p31 causes rapid loss of its inhibitory capacity and directly activates SUB1; the order of PMX cleavage sites on p31 was determined. Biochemical and enzymatic analysis; recombinant protein assays; dimerization analysis Biochimica et biophysica acta. General subjects Medium 38969256
2024 PMX processes the SUB1 prodomain within acidic secretory organelles; this processing is required for full SUB1 activation upon discharge into the parasitophorous vacuole at neutral pH, where the Sub1 prodomain mediates pH-dependent dimerization and autoinhibition. Crystal structure of full-length PfSub1; structural, biochemical, and biophysical studies including dimerization analysis mBio Medium 38386597
2022 PMX has a substrate consensus cleavage motif SFhE (h = hydrophobic amino acid); PMX prefers Phe in the P1 position, di-substitution at the β-carbon of the P2 moiety, and a hydrophobic P3 group, as established by peptidomimetic inhibitor structure-activity analysis and modeling. Enzymatic inhibition assays with peptidomimetics; substrate processing assays; molecular modelling ChemMedChem Medium 35906744
2009 A P. falciparum line overexpressing PMX showed fourfold reduced susceptibility to the diphenylurea compound GB-III-32, suggesting PMX is an alternative target for certain aspartic protease inhibitors that act early in the intraerythrocytic life cycle. Overexpression of PMX; drug susceptibility assay (IC50 comparison) Antimicrobial agents and chemotherapy Low 19752273
2022 HIV-1 protease inhibitors ritonavir (RTV) and lopinavir (LPV) inhibit PMX enzymatic activity; RTV binds to the PMX active site as shown by inhibition assay, representing the first report of PMX inhibition by an HIV-1 protease inhibitor. Enzymatic inhibition assay with recombinant PMX; crystal structure of PMII-drug complexes (structural inference for PMX active site) Current research in structural biology Low 38304146
2025 Crystal structure of PMX bound to macrocyclic peptidomimetic inhibitor 7k at 1.7 Å reveals PMX adopts a novel conformation upon 7k binding, involving significant movement of the S2'S2 loop and S2 flap leading to partial active site closure; catalytic aspartates D266 and D467 directly interact with the hydroxyethylamine pharmacophore. X-ray crystallography at 1.7 Å; molecular docking Journal of molecular biology High 40043835
2026 A 2-piperazino-pyrimidine compound (FPSA) targets PMX in P. falciparum: resistant parasite selection identified SNVs (I252V or E55G) and gene duplications in the PMX-encoding locus; genome-edited parasites with these substitutions showed reduced FPSA susceptibility; FPSA inhibited recombinant PMX proteolytic activity in vitro and blocked PMX substrate processing in parasites. Forward genetics (resistant parasite selection and whole-genome sequencing); CRISPR genome editing; in vitro enzymatic assay with recombinant PMX; substrate processing assay in parasites; transcriptomics International journal for parasitology. Drugs and drug resistance High 42025246
2023 Preprint version: PMX directly cleaves both p31 and p54 of SUB1 using recombinant proteins; cleavage sites on p31 were mapped; p54 is fully functional once p31 is removed, demonstrating that conversion to p47 is dispensable for SUB1 activity. Heterologous protease-mediated relief of propiece inhibition is established as the mechanism for PMX-dependent SUB1 activation. Recombinant protein cleavage assay; cleavage site mapping; conditional PMX knockdown; immunoblot bioRxivpreprint Medium 36712005

Source papers

Stage 0 corpus · 32 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2001 Aspartic proteases of Plasmodium falciparum and other parasitic protozoa as drug targets. Trends in parasitology 254 11872398
2017 Plasmepsins IX and X are essential and druggable mediators of malaria parasite egress and invasion. Science (New York, N.Y.) 145 29074774
2017 A multistage antimalarial targets the plasmepsins IX and X essential for invasion and egress. Science (New York, N.Y.) 121 29074775
2020 Dual Plasmepsin-Targeting Antimalarial Agents Disrupt Multiple Stages of the Malaria Parasite Life Cycle. Cell host & microbe 107 32109369
2009 Role of Plasmodium falciparum digestive vacuole plasmepsins in the specificity and antimalarial mode of action of cysteine and aspartic protease inhibitors. Antimicrobial agents and chemotherapy 67 19752273
2022 Discovery and Characterization of Potent, Efficacious, Orally Available Antimalarial Plasmepsin X Inhibitors and Preclinical Safety Assessment of UCB7362. Journal of medicinal chemistry 28 36216349
2020 An Endoplasmic Reticulum CREC Family Protein Regulates the Egress Proteolytic Cascade in Malaria Parasites. mBio 27 32098818
2016 Plasmodium falciparum ookinete expression of plasmepsin VII and plasmepsin X. Malaria journal 27 26911483
2022 Basis for drug selectivity of plasmepsin IX and X inhibition in Plasmodium falciparum and vivax. Structure (London, England : 1993) 24 35460613
2023 Activation of the Plasmodium Egress Effector Subtilisin-Like Protease 1 Is Mediated by Plasmepsin X Destruction of the Prodomain. mBio 19 37036362
2023 Plasmepsin X activates the PCRCR complex of Plasmodium falciparum by processing PfRh5 for erythrocyte invasion. Nature communications 17 37072430
2022 Maturation and substrate processing topography of the Plasmodium falciparum invasion/egress protease plasmepsin X. Nature communications 16 35927261
2022 Structures of plasmepsin X from Plasmodium falciparum reveal a novel inactivation mechanism of the zymogen and molecular basis for binding of inhibitors in mature enzyme. Protein science : a publication of the Protein Society 15 35048450
2023 Macrocyclic Peptidomimetic Plasmepsin X Inhibitors with Potent In Vitro and In Vivo Antimalarial Activity. Journal of medicinal chemistry 14 37505188
2022 Substrate Peptidomimetic Inhibitors of P. falciparum Plasmepsin X with Potent Antimalarial Activity. ChemMedChem 13 35906744
2024 Prodomain-driven enzyme dimerization: a pH-dependent autoinhibition mechanism that controls Plasmodium Sub1 activity before merozoite egress. mBio 8 38386597
2023 Susceptibility of Ugandan Plasmodium falciparum Isolates to the Antimalarial Drug Pipeline. Microbiology spectrum 8 37158739
2023 Design, synthesis and modelling of photoreactive chemical probes for investigating target engagement of plasmepsin IX and X in Plasmodium falciparum. RSC chemical biology 8 38179191
2022 Bridging the Gap in Malaria Parasite Resistance, Current Interventions, and the Way Forward from in Silico Perspective: A Review. Molecules (Basel, Switzerland) 8 36432016
2024 The malaria parasite egress protease SUB1 is activated through precise, plasmepsin X-mediated cleavage of the SUB1 prodomain. Biochimica et biophysica acta. General subjects 6 38969256
2025 Structure-activity analysis of imino-pyrimidinone-fused pyrrolidines aids the development of dual plasmepsin V and plasmepsin X inhibitors. The FEBS journal 4 40035447
2017 Targeting Plasmodium Proteases to Block Malaria Parasite Escape and Entry. Trends in parasitology 4 29269028
2024 Inhibition of Plasmodium falciparum plasmepsins by drugs targeting HIV-1 protease: A way forward for antimalarial drug discovery. Current research in structural biology 3 38304146
2025 Structural Plasticity of Plasmodium falciparum Plasmepsin X to Accommodate Binding of Potent Macrocyclic Hydroxyethylamine Inhibitors. Journal of molecular biology 2 40043835
2024 The antimalarial activity of transdermal N-89 mediated by inhibiting ERC gene expression in P. Berghei-infected mice. Parasitology international 1 39740755
2026 Unlocking the Enigmas of Plasmodium Aspartyl Protease in Antimalarial Therapy: Flap Region Dynamics and Enzyme Repression of Non-Food Vacuole Using Molecular Dynamics Simulations. Current pharmaceutical design 0 40457971
2026 A novel 2-piperazino-pyrimidine compound exhibits asexual antimalarial activity by targeting Plasmodium falciparum plasmepsin X. International journal for parasitology. Drugs and drug resistance 0 42025246
2026 Conformational Dynamics of Plasmepsin X during Inhibitor Binding. The journal of physical chemistry. B 0 42126260
2026 Plasmepsins as Antimalarial Drug Targets-Then, Now, and the Future. Medicinal research reviews 0 42227058
2026 2-Amino-3,4-Dihydroquinazolines Exhibit Potent Antimalarial Activity by Targeting Plasmepsin X. ACS infectious diseases 0 42424440
2025 Unravelling therapeutic potentials of Solanum anomalum fruits: antiplasmodial, hepatoprotective, and anti-oxidative stress activities, semi-purification, GC-MS, and in silico profiling. Journal of parasitic diseases : official organ of the Indian Society for Parasitology 0 40901435
2023 Activation of the Plasmodium egress effector subtilisin-like protease 1 is achieved by plasmepsin X destruction of the propiece. bioRxiv : the preprint server for biology 0 36712005