TUFA

TUFA (PF3D7_API02900) is the apicoplast-genome-encoded translation elongation factor Tu (EF-Tu) of Plasmodium falciparum, and it functions in protein synthesis within the apicoplast, the organelle to which its protein product localizes and in which it is translated, with expression peaking in the trophozoite stage (PMID:15773980, PMID:9045615). As a canonical elongation factor, recombinant PfEF-Tu hydrolyses GTP and undergoes GDP/GTP nucleotide exchange catalysed by its physical partner, the nuclear-encoded EF-Ts (PfEF-Ts), whose binding induces structural changes that would promote GDP release (PMID:21163263). Beyond its translation role, PfEF-Tu carries a chaperone-related disulphide reductase activity, a property advanced as a rationale for retention of the tufA gene on the plastid genome (PMID:21163263). TUFA is the direct molecular target of structurally distinct antibiotics: recombinant PfEF-Tu forms in vitro complexes with kirromycin, GE2270A, and enacyloxin IIa at different sites, and kirromycin inhibits its GTPase activity, while apicoplast-translation-disrupting drugs thiostrepton and clarithromycin reduce EF-Tu expression (PMID:15773980, PMID:10505418, PMID:21163263, PMID:26164186). All of these inhibitors show antimalarial activity, marking apicoplast translation via TUFA as an antimalarial vulnerability (PMID:10505418).

1. 1997 Medium

   Establishing where tufA physically resides answered whether this elongation factor belongs to the parasite's organellar genome and clarified the evolutionary origin of that genome.

   Evidence In situ hybridization localizing the 35-kb DNA to a four-membrane organelle and phylogenetic analysis of tufA sequences across apicomplexans

   PMID:9045615

   Open questions at the time

   • Does not demonstrate that the tufA-encoded protein is functional as an elongation factor
   • No evidence on protein localization or expression timing
   • No functional or drug-target data
2. 1999 Medium

   Identifying that recombinant PfEF-Tu binds structurally distinct antibiotics at different sites established the protein as a druggable antimalarial target, not merely a genomic feature.

   Evidence In vitro complex formation of recombinant EF-Tu with kirromycin, GE2270A, and enacyloxin IIa, plus blood-culture antimalarial assays

   PMID:10505418

   Open questions at the time

   • Binding shown in vitro but effect on EF-Tu catalytic activity not measured here
   • Single lab; no structural mapping of binding sites
   • No demonstration that antimalarial activity operates through EF-Tu inhibition in vivo
3. 2005 Medium

   Localizing the EF-Tu protein and its stage-specific expression answered whether tufA is translated and functions inside the apicoplast, linking it to thiostrepton's site of action.

   Evidence Immunolocalization to the apicoplast, stage-specific Western blots, and EF-Tu quantification after thiostrepton treatment

   PMID:15773980

   Open questions at the time

   • Reduction of EF-Tu by thiostrepton is indirect (via rRNA binding), not direct drug-EF-Tu interaction
   • Does not resolve EF-Tu catalytic mechanism
   • Single-lab evidence
4. 2010 High

   Reconstituting the catalytic cycle answered how PfEF-Tu operates enzymatically and with which partner, and confirmed kirromycin acts on its GTPase, while revealing an unexpected chaperone activity.

   Evidence Recombinant GTPase and nucleotide-exchange assays, PfEF-Tu/PfEF-Ts interaction, kirromycin inhibition in vitro, homology modelling, and GFP-leader targeting of EF-Ts

   PMID:21163263

   Open questions at the time

   • Structural model of the EF-Tu/EF-Ts complex is homology-based, not experimentally determined
   • Physiological substrates of the disulphide reductase activity not identified
   • In vivo consequences of blocking nucleotide exchange not tested
5. 2015 Low

   Testing clarithromycin's effect on TUFA expression addressed whether this macrolide's antimalarial action operates through disruption of apicoplast translation.

   Evidence qPCR and Western blotting of tufA mRNA and EF-Tu protein after clarithromycin treatment in Pf3D7 and PfK1 strains

   PMID:26164186

   Open questions at the time

   • No mechanistic dissection of how clarithromycin affects apicoplast translation; limited controls
   • Downregulation may be a downstream consequence rather than a direct effect on TUFA
   • Effect on EF-Tu catalytic function not measured

• The in vivo essentiality of TUFA and the native substrates of its chaperone-related disulphide reductase activity remain unresolved.
• No genetic knockout or conditional depletion of tufA reported in the corpus
• No experimentally determined structure of PfEF-Tu or its complex with EF-Ts
• Physiological targets and biological role of the disulphide reductase activity unknown