Mutations in the Chromodomain-like Insertion of Translation Elongation Factor 3 Compromise Protein Synthesis through Reduced ATPase Activity

Abstract

Background: Eukaryotic translation elongation factor 3 (eEF3) is a ribosome binding ATPase essential for fungal protein synthesis. Results: Mutations in the chromodomain-like insertion in an ATPase domain of eEF3 reduce ATPase activity but not ribosome binding. Conclusion:The chromodomain-like insertion affects the ATPase activity of eEF3 and translation. Significance: The chromodomain-like insertion of eEF3 may be targeted to develop new antifungal compounds.Translation elongation is mediated by ribosomes and multiple soluble factors, many of which are conserved across bacteria and eukaryotes. During elongation, eukaryotic elongation factor 1A (eEF1A; EF-Tu in bacteria) delivers aminoacylated-tRNA to the A-site of the ribosome, whereas eEF2 (EF-G in bacteria) translocates the ribosome along the mRNA. Fungal translation elongation is striking in its absolute requirement for a third factor, the ATPase eEF3. eEF3 binds close to the E-site of the ribosome and has been proposed to facilitate the removal of deacylated tRNA from the E-site. eEF3 has two ATP binding cassette (ABC) domains, the second of which carries a unique chromodomain-like insertion hypothesized to play a significant role in its binding to the ribosome. This model was tested in the current study using a mutational analysis of the Sac7d region of the chromodomain-like insertion. Specific mutations in this domain result in reduced growth rate as well as slower translation elongation. In vitro analysis demonstrates that these mutations do not affect the ability of eEF3 to interact with the ribosome. Kinetic analysis revealed a larger turnover number for ribosomes in comparison to eEF3, indicating that the partial reactions involving the ribosome are significantly faster than that of eEF3. Mutations in the chromodomain-like insertion severely compromise the ribosome stimulated ATPase of eEF3, strongly suggesting that it exerts an allosteric effect on the hydrolytic activity of eEF3. The chromodomain-like insertion is, therefore, vital to eEF3 function and may be targeted for developing novel antifungal drugs.Translation is a multistep process during which the information in the mRNA is decoded into polypeptides by the ribosome with the help of numerous soluble factors. During translation initiation, in a series of highly regulated steps catalyzed by the eukaryotic initiation factors (eIFs), a fully functional 80 S ribosome is assembled at the start codon of the mRNA open reading frame (1). This is followed by translation elongation, a cyclical process that involves aminoacyl-tRNA (aa-tRNA) 2 delivery, peptide bond formation, and translocation, facilitated by the eukaryotic elongation factors (eEFs) (2). The canonical GTPase elongation factors that are also highly conserved in bacteria function at the ribosome and play an important role in the accuracy of gene expression by maintaining the correct reading frame of the mRNA and assuring the access of cognate aa-tRNA to the ribosomal A-site (3). eEF1A is responsible for the delivery of aa-tRNA to the ribo...

Translation Elongation Factor 1A Mutants with Altered Actin Bundling Activity Show Reduced Aminoacyl-tRNA Binding and Alter Initiation via eIF2α Phosphorylation

“…Therefore, we wanted to determine whether a general defect in translation would be enough to cause an increase in eIF2␣ phosphorylation levels. Analysis of other eEF1A as well as eEF2 and eEF3 mutants known to affect translation elongation (29,30) showed that increased eIF2␣ phosphorylation does not result from a general reduction in translation elongation (Fig. 1B).…”

“…1B). To determine whether the phosphorylation effect was due to a general inhibition of translation, we analyzed the level of eIF2␣ phosphorylation in eEF2 and eEF3 mutants with established translation elongation defects (29,30). Neither of the eEF2 and eEF3 mutants gave rise to increased eIF2␣ phosphorylation (Fig.…”

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“…The chromodomain interacts through multiple sites with the ribosome. While mutation of ribosome-contacting residues in the chromodomain did not affect ribosome binding, they did impair cell growth, elongation rate, and ribosome-stimulated ATPase activity (Sasikumar and Kinzy 2014). Interestingly, many of the eEF3 mutations isolated in screens based on different eEF3 functions cause inhibition of the ATPase activity, indicating the central role of this activity to eEF3 function on the ribosome.…”

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