GATB

GATB (PF3D7_0628800) is the B subunit of a unique heterodimeric glutamyl-tRNA amidotransferase (GatAB) in Plasmodium falciparum, functioning in the indirect aminoacylation pathway that generates correctly charged Gln-tRNA(Gln) (PMID:26318454). Recombinant GatAB, formed by GATB together with the GatA subunit, converts mischarged Glu-tRNA(Gln) to Gln-tRNA(Gln) in vitro, establishing the transamidation activity of the complex (PMID:26318454). GATB localizes to the apicoplast in blood-stage parasites, placing this activity within the organellar translation machinery (PMID:26318454). Genetic evidence that the GatA subunit of the complex cannot be deleted in P. berghei blood-stage parasites indicates the GatAB complex is essential for erythrocytic-stage survival (PMID:26318454). Beyond its role as the B subunit of this heterodimeric amidotransferase, no further GATB-specific mechanistic detail has been characterized in the available corpus.

1. 2015 High

   Whether P. falciparum uses an indirect route to produce Gln-tRNA(Gln) and which enzyme performs the transamidation was unknown; reconstitution established that GATB, as part of the heterodimeric GatAB complex, catalyzes conversion of Glu-tRNA(Gln) to Gln-tRNA(Gln).

   Evidence Recombinant protein expression and in vitro amidotransferase assay

   PMID:26318454

   Open questions at the time

   • The specific catalytic contribution of the GATB subunit versus GatA within the complex is not dissected
   • No structural model of the GATB-GatA heterodimer
   • Substrate/tRNA recognition determinants attributable to GATB not defined
2. 2015 Medium

   The subcellular compartment in which GATB acts was unknown; localization placed GATB in the apicoplast, tying its amidotransferase activity to organellar translation in blood-stage parasites.

   Evidence Subcellular localization by fluorescence microscopy/fractionation

   PMID:26318454

   Open questions at the time

   • Single method, single lab localization
   • Import/targeting mechanism of GATB to the apicoplast not addressed
   • Localization across other life-cycle stages not examined
3. 2015 Medium

   Whether the GatAB pathway is dispensable was unknown; failure to delete the GatA subunit indicated the complex is required for erythrocytic-stage survival.

   Evidence Failed gene knockout of the GatA subunit in P. berghei blood-stage parasites in vivo

   PMID:26318454

   Open questions at the time

   • Essentiality was demonstrated via GatA, not by direct deletion of GATB itself
   • Conditional knockdown to confirm GATB-specific essentiality not performed
   • Requirement in non-blood stages not tested

• The GATB-specific catalytic mechanism, structural organization within GatAB, and direct genetic essentiality of GATB itself remain unresolved.
• No direct GATB knockout or knockdown reported
• No structural characterization of GATB
• Regulation and stage-specific function unknown