PTEF

PTEF (PF3D7_0202400) is a non-canonical translation-enhancing factor in Plasmodium falciparum that couples proteolytic processing to the translational control of the placental cytoadherence ligand VAR2CSA (PMID:28481333). PTEF is cleaved by PfCalpain, a step that liberates a C-terminal domain containing a sterile-alpha-motif (SAM)-like fold (PMID:28481333). This released C-terminal domain shuttles to the cytoplasm and associates directly with ribosomes, where it relieves upstream open reading frame (uORF)-mediated repression of the var2csa coding sequence, so that VAR2CSA protein output in var2csa-transcribing parasites scales with PTEF expression level (PMID:28481333). The isolated C-terminal domain enhances translation in a heterologous system, establishing PTEF's intrinsic translation-enhancing activity (PMID:28481333). Through this control of VAR2CSA translation, PTEF activity governs the CSA-binding adhesion phenotype of infected erythrocytes (PMID:28481333). Beyond this processing-and-derepression mechanism defined in a single study, no further mechanistic detail on PTEF has been characterized in the available corpus.

1. 2017 High

   Established that VAR2CSA translation is not solely transcriptionally controlled but depends on a dedicated factor that overcomes uORF repression, identifying PTEF as that factor.

   Evidence Genetic manipulation of PTEF expression with measurement of VAR2CSA protein output in P. falciparum

   PMID:28481333

   Open questions at the time

   • Does not define how PTEF specifically recognizes the var2csa uORF versus other uORF-containing transcripts
   • Quantitative relationship between PTEF dose and derepression not fully mapped
2. 2017 High

   Explained how PTEF is activated, showing that its function requires PfCalpain cleavage to release a C-terminal SAM-like domain rather than acting as a full-length protein.

   Evidence In vitro and cellular proteolytic processing assays identifying PfCalpain, with domain characterization, in P. falciparum

   PMID:28481333

   Open questions at the time

   • Trigger and timing of PfCalpain cleavage during the cell cycle not established
   • Fate and function of the non-C-terminal portion of PTEF unknown
3. 2017 High

   Localized the active fragment and its target, showing the cleaved C-terminal domain shuttles to the cytoplasm and binds ribosomes to derepress var2csa translation.

   Evidence Subcellular localization (cytoplasmic shuttling) and ribosome interaction/co-fractionation assays in P. falciparum

   PMID:28481333

   Open questions at the time

   • Ribosomal contact site and stoichiometry not resolved
   • Mechanism by which ribosome association overrides uORF stalling not defined
4. 2017 Medium

   Demonstrated the C-terminal domain has intrinsic translation-enhancing activity independent of the parasite context.

   Evidence Heterologous cell-free/non-Plasmodium translation assay with the PTEF C-terminal domain

   PMID:28481333

   Open questions at the time

   • Heterologous system may not recapitulate Plasmodium-specific cofactor requirements
   • Not reconstituted with defined ribosomal components
   • Single lab, single study
5. 2017 Medium

   Connected PTEF's translational role to a disease-relevant phenotype, showing PTEF activity controls CSA-binding of infected erythrocytes.

   Evidence Functional CSA binding assay in parasites with manipulated PTEF expression

   PMID:28481333

   Open questions at the time

   • Contribution of PTEF to adhesion phenotypes mediated by other PfEMP1 variants not tested
   • In vivo relevance to placental sequestration not addressed
   • Single paper

• How PTEF selectively targets particular uORF-containing mRNAs, the structural basis of its ribosome interaction, and its broader role in the parasite translatome remain unknown.
• No structure of PTEF or its ribosome complex
• Transcript selectivity determinants unknown
• Whether PTEF regulates targets beyond var2csa uncharacterized