Plasmodium protein phosphatase 2C dephosphorylates translation elongation factor 1β and inhibits its PKC-mediated nucleotide exchange activity in vitro

The elongation step of protein synthesis involves binding of aminoacyl-tRNA to the ribosomal A site, formation of a peptide bond and translocation of the newly formed peptidyl-tRNA to the P site. The nucleotide exchange factor EF-1β plays a major role in the regulation of this process by regenerating a GTP-bound EF-1α necessary for each elongation cycle. EF-1β has been shown to be phosphorylated and its phosphorylation is critical for optimal activity. We have previously identified a serine/threonine protein phosphatase 2C (PP2C) from the human malaria parasite Plasmodium falciparum. In the current work, we performed Far-Western analysis to identify PfPP2C substrates. Several components of the translation and transcription machinery were identified, including translation elongation factor 1-beta (PfEF-1β). PfEF-1β is efficiently phosphorylated by protein kinase C and this phosphorylation results in a 400% increase in its nucleotide exchange activity. PKC-phosphorylated PfEF-1β is readily and selectively dephosphorylated by recombinant and native PfPP2C, which downregulates the nucleotide exchange activity to its basal level. The identification of a translation elongation component as substrate for PP2C suggests an important regulatory function for this enzyme and suggests that it may be a good target for drug design in the fight against malaria.