EF-1beta

EF-1beta (PF3D7_0913200) is a nucleotide exchange factor of the Plasmodium falciparum translation elongation machinery, regenerating GTP-bound EF-1alpha for successive elongation cycles (PMID:11251817). Its exchange activity is dynamically regulated by reversible phosphorylation: protein kinase C phosphorylates EF-1beta and raises its nucleotide exchange activity roughly four-fold (PMID:11251817), while P. falciparum protein phosphatase 2C (PfPP2C) selectively dephosphorylates it and returns activity to basal levels, defining a writer/eraser pair that tunes EF-1beta output (PMID:11251817). In native parasites EF-1beta assembles into a multi-subunit elongation factor complex containing at least two copies of itself together with EF-1alpha, EF-1gamma, and EF-1delta (PMID:17307963). Beyond this biochemical and complex-membership picture, no structural model, in vivo essentiality data, or higher-resolution mechanism of EF-1beta has been characterized in the available corpus.

1. 2001 Medium

   Establishing that EF-1beta acts as a phosphorylation-controlled nucleotide exchange factor answered how P. falciparum couples a signaling kinase to the rate of GTP regeneration on EF-1alpha during elongation.

   Evidence In vitro PKC kinase assay coupled to a nucleotide exchange activity assay in P. falciparum

   PMID:11251817

   Open questions at the time

   • Phosphosite(s) on EF-1beta not mapped
   • Functional consequence shown in vitro only, not in intact parasites
   • Identity of the physiological PKC-type kinase in vivo not established
2. 2001 Medium

   Identifying PfPP2C as the phosphatase that reverses PKC phosphorylation defined the eraser side of a reversible switch controlling EF-1beta exchange activity.

   Evidence Far-Western substrate identification plus in vitro dephosphorylation with recombinant and native PfPP2C and a nucleotide exchange readout in P. falciparum

   PMID:11251817

   Open questions at the time

   • In vivo relevance of the phosphorylation/dephosphorylation cycle not demonstrated
   • Whether PfPP2C acts on EF-1beta within the native complex is unknown
   • Stoichiometry and kinetics of the switch not quantified
3. 2007 Medium

   Native purification defined the composition of the EF-1beta-containing elongation factor complex, showing EF-1beta is a multi-copy subunit assembled with EF-1alpha, EF-1gamma, and EF-1delta.

   Evidence Tandem affinity purification of PTP-tagged EF-1beta from transgenic parasites followed by mass spectrometry in P. falciparum

   PMID:17307963

   Open questions at the time

   • No structural model or subunit arrangement determined
   • How phosphorylation state affects complex assembly or activity not tested
   • Direct binary interactions among subunits not resolved

• Whether EF-1beta is essential in blood-stage parasites and how its phosphorylation cycle is integrated into translational control in vivo remains unresolved.
• No genetic knockout/knockdown phenotype in the corpus
• No in vivo demonstration of the PKC/PfPP2C regulatory cycle
• No structural characterization of EF-1beta or its complex