PMT

PMT (PF3D7_1343000) is a phosphoethanolamine N-methyltransferase that supplies phosphocholine for phosphatidylcholine biosynthesis in Plasmodium falciparum, and it is essential for both intraerythrocytic asexual growth and transmission to mosquitoes (PMID:15073329, PMID:18694927, PMID:24145416). As a monopartite single-domain enzyme, PMT catalyzes all three sequential SAM-dependent methylation steps that convert phosphoethanolamine to phosphocholine, acting specifically on the free phosphobase rather than on phosphatidylethanolamine, and its product feeds directly into the Kennedy (CDP-choline) pathway (PMID:15073329, PMID:15664981). Because P. falciparum lacks phosphatidylethanolamine-to-phosphatidylcholine methylation, genetic ablation of PMT abolishes phosphatidylcholine synthesis via the serine-decarboxylase-phosphoethanolamine-methyltransferase route and impairs parasite growth and viability, while PMT-null parasites fail to produce mature gametocytes and cannot be transmitted to mosquitoes (PMID:18694927, PMID:24145416). High-resolution crystal structures with substrate, product, cofactor, and inhibitors, combined with extensive mutagenesis and QM/MM analysis, define an active site in which Asp-128 mediates proton transfer through a bridging water to enable SN2 methyl transfer from SAM, with Tyr-19 and His-132 contributing to ligand positioning (PMID:22117061, PMID:25288796). Enzyme abundance and activity are tightly controlled: choline both represses PfPMT transcription and drives proteasomal degradation of the protein (PMID:17644653), and PMT is phosphorylated by PfCDPK7 downstream of the PfPI4K/PfCDPK7 signaling axis, with loss of PfCDPK7 leaving PMT hypophosphorylated and degraded (PMID:34866326). The enzyme localizes to the Golgi apparatus (PMID:16704982) and is inhibited by product phosphocholine, miltefosine, amodiaquine, and other compounds, making it a validated antimalarial target (PMID:15073329, PMID:20085640, PMID:24145416).

1. 2004 High

   Establishing the core biochemical activity answered what PMT does: it defined the enzyme as a single-domain catalyst performing all three methylations converting phosphoethanolamine to phosphocholine.

   Evidence Biochemical characterization of recombinant enzyme with in vitro methylation assays and product/analog inhibition

   PMID:15073329

   Open questions at the time

   • Did not establish the in vivo substrate specificity
   • No structural basis for catalysis at this stage
2. 2005 High

   Yeast complementation resolved whether PMT acts on the free phosphobase or the lipid and how its product connects to lipid synthesis, showing phosphoethanolamine is the in vivo substrate coupled to the Kennedy pathway.

   Evidence Complementation of yeast pem1Δpem2Δ mutant with epistasis via choline-phosphate cytidylyltransferase mutation and lipid analysis

   PMID:15664981

   Open questions at the time

   • Yeast surrogate may not fully recapitulate parasite context
   • Did not address subcellular localization in the parasite
3. 2006 High

   Localization studies answered where PMT operates in the parasite, placing the enzyme in the Golgi apparatus and revealing stage-dependent abundance.

   Evidence Confocal and immunoelectron microscopy with GFP organelle markers plus stage-resolved immunoblotting

   PMID:16704982

   Open questions at the time

   • Mechanism of Golgi targeting not defined
   • Functional significance of Golgi localization for phosphocholine supply unclear
4. 2007 High

   Regulation studies answered how PMT levels respond to nutrient availability, revealing dual control by choline at the transcriptional level and via proteasomal degradation.

   Evidence Transcript analysis, pulse-chase, immunoprecipitation, and bortezomib proteasome inhibition in wild-type and transgenic parasites

   PMID:17644653

   Open questions at the time

   • Degradation signal/E3 ligase not identified
   • Transcriptional repressor mediating choline response unknown
5. 2008 Medium

   Mutagenesis began mapping catalytically critical residues, identifying Asp-61, Gly-83, and Asp-128 as required for activity and cofactor/substrate binding.

   Evidence Site-directed mutagenesis of 24 residues scored by yeast complementation

   PMID:18178564

   Open questions at the time

   • No structural validation at this stage
   • Functional readout limited to yeast survival, not direct kinetics
6. 2008 High

   Genetic knockout answered whether PMT is dispensable, showing it is required for phosphatidylcholine synthesis via the SDPM pathway and for asexual growth, and defining the pathway architecture in P. falciparum.

   Evidence Genetic knockout with lipid analysis and growth/viability assays

   PMID:18694927

   Open questions at the time

   • Did not address sexual-stage requirement
   • Residual growth via CDP-choline pathway not fully quantified
7. 2010 Medium

   Species comparison addressed conservation of the pathway, showing PMT activity and gene are absent in rodent Plasmodium species, distinguishing P. falciparum phospholipid metabolism.

   Evidence In silico genome analysis and radiolabeling with choline, ethanolamine, and serine across P. falciparum and four rodent species

   PMID:19561325

   Open questions at the time

   • Does not clarify how rodent parasites compensate for the missing route
   • Limits use of rodent models to study PMT function in vivo
8. 2010 Medium

   Inhibitor profiling identified small molecules that block PMT and demonstrated direct binding, advancing PMT as a druggable target.

   Evidence Enzyme-coupled methylation assay, NMR titration binding, and yeast surrogate sensitivity with amodiaquine and quaternary ammonium compounds

   PMID:20085640

   Open questions at the time

   • No structural basis for inhibitor binding yet
   • Selectivity over human methyltransferases untested
9. 2011 High

   High-resolution crystallography with substrate, product, cofactor, and inhibitor resolved the structural mechanism, defining ligand-induced domain rearrangements and implicating a Tyr-19/His-132 catalytic dyad acting as a latch.

   Evidence Multiple X-ray structures (1.19–1.55 Å), mutagenesis of 27 residues, kinetics, and ITC

   PMID:22117061

   Open questions at the time

   • Assignment of the catalytic base was later revised
   • Order of the three methylation steps not structurally resolved
10. 2012 High

    A PMT-amodiaquine complex structure provided the structural rationale for inhibitor binding at the active site, guiding structure-based inhibitor design.

    Evidence 2.0 Å X-ray structure with amodiaquine and IC50 determination across a series of aminoquinolines

    PMID:22771008

    Open questions at the time

    • Cellular potency and selectivity of aminoquinoline series not established here
11. 2013 High

    Transmission-stage genetics answered whether PMT matters beyond asexual growth, showing it is essential for gametocyte maturation and mosquito transmission, with a chemical inhibitor phenocopying the loss.

    Evidence Genetic knockout with gametocyte and mosquito transmission assays plus NSC-158011 inhibitor characterization and yeast complementation

    PMID:24145416

    Open questions at the time

    • Mechanistic basis of the gametocyte defect not resolved
    • Inhibitor specificity in vivo not fully defined
12. 2014 High

    Combined QM/MM, mutagenesis, and mutant crystal structures revised the catalytic mechanism, establishing Asp-128 as the proton acceptor via a bridging water preceding SN2 methyl transfer.

    Evidence QM/MM calculations, D128A/E/Q/N mutagenesis with activity assays, and crystal structures of the D128A mutant with SAH and phosphobase ligands

    PMID:25288796

    Open questions at the time

    • Whether later methylation steps use the same residue is not fully resolved
    • Roles of Tyr-19/His-132 reconciled but hierarchy of contributions still incomplete
13. 2015 High

    Structural and biochemical characterization of P. vivax and P. knowlesi orthologs tested conservation of the drug target, showing both are inhibited by amodiaquine and NSC158011.

    Evidence X-ray crystallography, inhibitor assays, and yeast metabolic labeling for PvPMT and PkPMT

    PMID:25761669

    Open questions at the time

    • Findings are on orthologs, not PF3D7_1343000 directly
    • Cross-species inhibitor potency in parasites not compared
14. 2021 Medium

    Signaling studies answered how PMT is regulated post-translationally, placing it downstream of the PfPI4K/PfCDPK7 axis where PfCDPK7 phosphorylation stabilizes the enzyme.

    Evidence Quantitative phosphoproteomics, lipidomics, conditional PfCDPK7 knockdown, and PI4K inhibitor treatment

    PMID:34866326

    Open questions at the time

    • Direct kinase-substrate relationship not reconstituted
    • Phosphosites on PMT and their functional consequences not mapped

• How Golgi localization, choline-driven turnover, and PfCDPK7 phosphorylation are integrated to control PMT-dependent phosphocholine flux across asexual and sexual stages remains unresolved.
• No integrated model linking regulatory inputs to phospholipid flux
• E3 ligase and phosphosites governing PMT stability unidentified
• Mechanistic cause of the gametocyte maturation defect unknown