Abstract
The translation factor IF6 is a protein of about 25 kDa shared by the Archaea and the Eukarya but absent in Bacteria. It acts as a ribosome anti-association factor that binds to the large subunit preventing the joining to the small subunit. It must be released from the large ribosomal subunit to permit its entry to the translation cycle. In Eukarya, this process occurs by the coordinated action of the GTPase Efl1 and the docking protein SBDS. Archaea do not possess a homolog of the former factor while they have a homolog of SBDS. In the past, we have determined the function and ribosomal localization of the archaeal (Sulfolobus solfataricus) IF6 homolog (aIF6) highlighting its similarity to the eukaryotic counterpart. Here, we analyzed the mechanism of aIF6 release from the large ribosomal subunit. We found that, similarly to the Eukarya, the detachment of aIF6 from the 50S subunit requires a GTPase activity which involves the archaeal elongation factor 2 (aEF-2). However, the release of aIF6 from the 50S subunits does not require the archaeal homolog of SBDS, being on the contrary inhibited by its presence. Molecular modeling, using published structural data of closely related homologous proteins, elucidated the mechanistic interplay between the aIF6, aSBDS, and aEF2 on the ribosome surface. The results suggest that a conformational rearrangement of aEF2, upon GTP hydrolysis, promotes aIF6 ejection. On the other hand, aSBDS and aEF2 share the same binding site, whose occupation by SBDS prevents aEF2 binding, thereby inhibiting aIF6 release.
Highlights
The process of protein synthesis is conserved in all living organisms and involves ribosomes, mRNA, and different translation factors
Later studies confirmed that the removal of eIF6 from the 60S subunit is a late event of ribosome biogenesis and that this step requires the combined action of the GTPase elongation factor-like GTPase 1 (Efl1) and SBDS (Bécam et al, 2001; Menne et al, 2007; Finch et al, 2011; Wong et al, 2011)
To elucidate the mechanism inducing archaeal (Sulfolobus solfataricus) IF6 homolog (aIF6) release we focused our attention on a simplified system consisting of just whole ribosomes
Summary
The process of protein synthesis is conserved in all living organisms and involves ribosomes, mRNA, and different translation factors. Later studies confirmed that the removal of eIF6 from the 60S subunit is a late event of ribosome biogenesis and that this step requires the combined action of the GTPase Efl and SBDS (Bécam et al, 2001; Menne et al, 2007; Finch et al, 2011; Wong et al, 2011). These two factors collaborate to a final quality control assessment for the integrity of the P-site and the GTPase center of the 60S subunit. Structural studies confirmed that the ribosome binding site of IF6 is the same as that of its eukaryotic counterpart (Greber et al, 2012)
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