RESUMO
Ribosome-driven protein biosynthesis is comprised of four phases: initiation, elongation, termination and recycling. In bacteria, ribosome recycling requires ribosome recycling factor and elongation factor G, and several structures of bacterial recycling complexes have been determined. In the eukaryotic and archaeal kingdoms, however, recycling involves the ABC-type ATPase ABCE1 and little is known about its structural basis. Here we present cryo-electron microscopy reconstructions of eukaryotic and archaeal ribosome recycling complexes containing ABCE1 and the termination factor paralogue Pelota. These structures reveal the overall binding mode of ABCE1 to be similar to canonical translation factors. Moreover, the iron-sulphur cluster domain of ABCE1 interacts with and stabilizes Pelota in a conformation that reaches towards the peptidyl transferase centre, thus explaining how ABCE1 may stimulate peptide-release activity of canonical termination factors. Using the mechanochemical properties of ABCE1, a conserved mechanism in archaea and eukaryotes is suggested that couples translation termination to recycling, and eventually to re-initiation.
Assuntos
Evolução Molecular , Pyrococcus furiosus/química , Ribossomos/química , Ribossomos/metabolismo , Saccharomyces cerevisiae/química , Transportadores de Cassetes de Ligação de ATP/química , Transportadores de Cassetes de Ligação de ATP/metabolismo , Proteínas de Ciclo Celular/química , Proteínas de Ciclo Celular/metabolismo , Microscopia Crioeletrônica , Endorribonucleases/química , Endorribonucleases/metabolismo , Proteínas Ferro-Enxofre/química , Proteínas Ferro-Enxofre/metabolismo , Modelos Moleculares , Movimento , Complexos Multiproteicos/química , Complexos Multiproteicos/metabolismo , Proteínas Nucleares/química , Proteínas Nucleares/metabolismo , Fatores de Terminação de Peptídeos/química , Fatores de Terminação de Peptídeos/metabolismo , Ligação Proteica , Estabilidade Proteica , Estrutura Terciária de Proteína , Pyrococcus furiosus/metabolismo , Ribossomos/ultraestrutura , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMO
No-go decay (NGD) is a mRNA quality-control mechanism in eukaryotic cells that leads to degradation of mRNAs stalled during translational elongation. The key factors triggering NGD are Dom34 and Hbs1. We used cryo-EM to visualize NGD intermediates resulting from binding of the Dom34-Hbs1 complex to stalled ribosomes. At subnanometer resolution, all domains of Dom34 and Hbs1 were identified, allowing the docking of crystal structures and homology models. Moreover, the close structural similarity of Dom34 and Hbs1 to eukaryotic release factors (eRFs) enabled us to propose a model for the ribosome-bound eRF1-eRF3 complex. Collectively, our data provide structural insights into how stalled mRNA is recognized on the ribosome and how the eRF complex can simultaneously recognize stop codons and catalyze peptide release.