CEPT

CEPT (PF3D7_0628300) is an endoplasmic reticulum-localized choline/ethanolaminephosphotransferase that catalyzes the terminal step of de novo phosphatidylcholine biosynthesis in Plasmodium and is essential for asexual blood-stage development (PMID:20478340, PMID:22471905). In P. berghei the gene is refractory to knockout, and GFP-tagging localizes the protein to the ER, distinguishing it from the cytosolic upstream Kennedy-pathway enzymes; sequence analysis confirms the catalytic domains and residues required for phosphotransferase activity (PMID:20478340). In P. falciparum, CEPT displays CDP-choline phosphotransferase activity with a Km of ~13 µM and is the primary molecular target of the antimalarial albitiazolium, which inhibits the enzyme in vitro and directly engages CEPT in living parasites as shown by competitive photocrosslinking with a clickable albitiazolium probe that co-localizes to the ER and trans-Golgi (PMID:22471905, PMID:25470252). CEPT protein levels fall upon pharmacological disruption of phospholipid synthesis without a matching transcriptional change, indicating post-transcriptional/post-translational regulation (PMID:18973684). Co-immunoprecipitation places CEPT in physical association with phosphatidylserine synthase at the ER (PMID:35623558), and its locus is marked by repressive H3K36me2/3 in stage II gametocytes, correlating with stage-specific transcriptional silencing (PMID:33794978). Beyond these findings, no further mechanistic detail on CEPT has been characterized in the available corpus.

1. 2008 Medium

   Established that CEPT protein abundance, but not transcript level, responds to bisthiazolium (T4) treatment that blocks PC synthesis, revealing a post-transcriptional/post-translational control layer coupled to phospholipid pathway status.

   Evidence Quantitative proteomics with parallel transcriptome profiling and metabolic radiolabelling in T4-treated P. falciparum

   PMID:18973684

   Open questions at the time

   • Mechanism of the post-translational downregulation not identified
   • Does not establish whether CEPT is a direct T4 target versus a downstream responder
2. 2010 Medium

   Determined that CEPT is essential for asexual blood-stage growth and localizes to the ER, unlike the cytosolic upstream Kennedy-pathway enzymes, placing the terminal biosynthetic step at the ER.

   Evidence Refractory gene-knockout attempts plus GFP-fusion live imaging and catalytic-domain sequence analysis in P. berghei

   PMID:20478340

   Open questions at the time

   • Essentiality inferred from refractory KO rather than conditional depletion
   • Enzymatic activity not directly demonstrated in this study
3. 2012 Medium

   Provided direct enzymatic characterization of CEPT as a CDP-choline phosphotransferase and linked the antimalarial albitiazolium to inhibition of this terminal PC-biosynthesis step.

   Evidence Radiolabelled-substrate activity assay with Michaelis-Menten kinetics (Km CDP-choline ~13 µM) and albitiazolium IC50 determination in P. falciparum extracts

   PMID:22471905

   Open questions at the time

   • Activity measured in crude extracts rather than purified recombinant enzyme
   • In vitro IC50 (~4.2 mM) leaves cellular relevance of inhibition unresolved
4. 2014 High

   Confirmed in living parasites that the albitiazolium pharmacophore directly engages CEPT, identifying it as the primary drug target and reinforcing ER/trans-Golgi localization.

   Evidence In-cell photocrosslinking with a bifunctional albitiazolium probe, click-chemistry affinity purification, mass spectrometry, and competitive displacement in P. falciparum

   PMID:25470252

   Open questions at the time

   • Binding site on CEPT not mapped
   • Whether target engagement fully accounts for antimalarial killing not established
5. 2021 Low

   Linked stage-specific transcriptional repression of the CEPT locus to repressive H3K36me2/3 chromatin marks during early gametocytogenesis.

   Evidence ChIP-seq for H3K36me2 and H3K36me3 in stage II gametocytes of P. falciparum

   PMID:33794978

   Open questions at the time

   • Chromatin association shown but no direct functional consequence for CEPT demonstrated
   • Causal role of the marks in silencing untested
6. 2022 Low

   Placed CEPT in physical proximity to phosphatidylserine synthase at the ER, suggesting spatial coordination of phospholipid biosynthesis.

   Evidence Co-immunoprecipitation via GFP-tagged PfPSS in transgenic P. falciparum with high-resolution microscopy

   PMID:35623558

   Open questions at the time

   • Single Co-IP without reciprocal validation
   • Direct versus indirect interaction not distinguished
   • Functional significance of the association untested

• How CEPT activity is regulated at the protein level in response to phospholipid supply, and the structural basis of albitiazolium binding, remain unresolved.
• No structural model of CEPT or its drug-binding site
• Mechanism of post-translational downregulation unknown
• No purified recombinant enzyme characterization