Structural Basis for Polyproline-Mediated Ribosome Stalling and Rescue by the Translation Elongation Factor EF-P

摘要

Summary Ribosomes synthesizing proteins containing consecutive proline residues become stalled and require rescue via the action of uniquely modified translation elongation factors, EF-P in bacteria, or archaeal/eukaryotic a/eIF5A. To date, no structures exist of EF-P or eIF5A in complex with translating ribosomes stalled at polyproline stretches, and thus structural insight into how EF-P/eIF5A rescue these arrested ribosomes has been lacking. Here we present cryo-EM structures of ribosomes stalled on proline stretches, without and with modified EF-P. The structures suggest that the favored conformation of the polyproline-containing nascent chain is incompatible with the peptide exit tunnel of the ribosome and leads to destabilization of the peptidyl-tRNA. Binding of EF-P stabilizes the P-site tRNA, particularly via interactions between its modification and the CCA end, thereby enforcing an alternative conformation of the polyproline-containing nascent chain, which allows a favorable substrate geometry for peptide bond formation. Graphical Abstract Display Omitted Highlights ? Polyproline-containing peptides stall translation by destabilizing the P-site tRNA ? Elongation factor EF-P recognizes the P-site tRNA and E-site mRNA codon ? The lysine modification of EF-P stabilizes the CCA end of the P-site tRNA ? EF-P promotes a favorable geometry of the P-site for peptide bond formation Huter et?al. present cryo-EM structures of polyproline-stalled ribosomes in the presence and absence of translation elongation factor EF-P. The structures reveal that polyproline sequences arrest translation by destabilizing the P-site tRNA, whereas binding of EF-P stabilizes the P-site tRNA and promotes a favorable geometry for peptide bond formation.