TUFA

PBANKA_API00280 (TUFA) encodes a plastid-genome-encoded elongation factor Tu that functions in translation within the Plasmodium apicoplast, the relict plastid acquired by secondary endosymbiosis (PMID:9045615). The EF-Tu protein is translationally active and localizes to the apicoplast, with maximal expression in the trophozoite stage of the intraerythrocytic cycle (PMID:15773980). As a translation factor, TUFA/EF-Tu hydrolyses GTP and physically interacts with its nuclear-encoded partner EF-Ts, which mediates nucleotide exchange (GDP release) on EF-Tu; the protein additionally possesses chaperone-related disulphide reductase activity, offering a rationale for retention of tufA on the plastid genome (PMID:21163263). TUFA is a validated antimalarial target: recombinant apicoplast EF-Tu forms complexes with the inhibitors kirromycin, GE2270A, and enacyloxin IIa, and kirromycin inhibits its GTPase activity in vitro (PMID:10505418, PMID:21163263). Disruption of apicoplast translation by thiostrepton and clarithromycin reduces EF-Tu/tufA levels, linking these antibiotics' antimalarial action to this factor (PMID:15773980, PMID:26164186). All direct evidence derives from the P. falciparum ortholog; TUFA has not been characterized in P. berghei in the available corpus.

1. 1997 Medium

   Established that tufA is a plastid-genome-encoded gene in Apicomplexa, defining the organellar context in which EF-Tu operates and placing the apicoplast in the cyanobacterial/plastid lineage.

   Evidence Phylogenetic analysis of tufA sequences and in situ hybridization localizing the 35 kb genome to a four-membrane organelle

   PMID:9045615

   Open questions at the time

   • Does not demonstrate that the tufA product is expressed or functional as a protein
   • No biochemical characterization of EF-Tu activity
   • Shown in P. falciparum only
2. 1999 Medium

   Answered whether apicoplast EF-Tu is druggable by showing recombinant PfEF-Tu binds three distinct EF-Tu inhibitors that also inhibit parasite growth, establishing TUFA as an antimalarial translation-factor target.

   Evidence In vitro complex-formation assays between recombinant PfEF-Tu and kirromycin, GE2270A, enacyloxin IIa; blood-culture growth inhibition

   PMID:10505418

   Open questions at the time

   • Binding shown in vitro without demonstration of the functional consequence on translation at that time
   • Did not confirm that growth inhibition is mediated specifically through EF-Tu in vivo
   • Shown in P. falciparum only
3. 2005 Medium

   Demonstrated that the tufA product is translationally active and organelle-resident, confirming EF-Tu operates inside the apicoplast and is stage-regulated.

   Evidence Immunofluorescence localization of EF-Tu to the apicoplast, stage-specific expression analysis, and Western blot showing thiostrepton reduces EF-Tu levels

   PMID:15773980

   Open questions at the time

   • Correlative link to thiostrepton action rather than direct target engagement
   • Does not resolve the enzymatic mechanism of EF-Tu
   • Shown in P. falciparum only
4. 2010 High

   Resolved the biochemical mechanism of TUFA/EF-Tu, showing it is a GTPase whose nucleotide cycle is driven by its nuclear-encoded EF-Ts partner and that it carries an additional disulphide reductase (chaperone) activity, explaining plastid retention of the gene.

   Evidence Recombinant GTPase, nucleotide-exchange, and disulphide reductase assays; EF-Tu:EF-Ts interaction assay; kirromycin GTPase inhibition; homology modeling; GFP targeting of EF-Ts to apicoplast

   PMID:21163263

   Open questions at the time

   • Structural model is homology-based, not an experimental structure
   • Physiological substrates/aminoacyl-tRNA delivery not directly reconstituted
   • Shown in P. falciparum only
5. 2015 Low

   Extended the antibiotic-vulnerability of apicoplast translation by showing clarithromycin downregulates tufA at mRNA and protein levels, implicating this pathway in the drug's antimalarial mechanism.

   Evidence qPCR and Western blot of tufA/EF-Tu after clarithromycin treatment in Pf3D7 and PfK1 strains

   PMID:26164186

   Open questions at the time

   • Single-approach expression measurement with no functional rescue or mechanistic dissection
   • Does not establish whether tufA downregulation is cause or consequence of translation disruption
   • Shown only in P. falciparum strains 3D7 and K1

• Whether the P. berghei ortholog PBANKA_API00280 itself (as opposed to the P. falciparum ortholog) is essential in vivo and whether its inhibitors act through EF-Tu genetically remains unaddressed in the corpus.
• No loss-of-function or conditional knockdown data for the gene
• No experimental structure of the EF-Tu:EF-Ts complex
• No data specific to P. berghei