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Modification, inhibition and function of elongation factor EF-P

Subject Area Biochemistry
Term from 2015 to 2019
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 265881756
 
Final Report Year 2019

Final Report Abstract

Protein synthesis in the cell occurs on macromolecular machines called ribosomes. The ribosome synthesizes polypeptide chains by providing a platform upon which peptide-bond formation can occur between a peptidyl-tRNA located at the ribosomal P-site and an amino acyl-tRNA in the A-site. However, the ribosome cannot form peptide bonds between all amino acids with the same efficiency; this is exemplified by the amino acid proline. Proline, which has an imino group instead of a primary amino group in other amino acids, has been shown to be a particularly poor substrate for peptide-bond formation, both as a donor in the P-site and as an acceptor in the A-site. In fact, ribosomes stall when attempting to incorporate three or more consecutive proline residues (PPP) into the polypeptide chain. This translational arrest due to polyproline stretches is relieved by the translation elongation factor EF-P in bacteria and a/eIF-5A in archaea/eukaryotes, however, a structural basis for this rescue has been lacking. Here we have determined cryo-EM structures of polyproline-stalled ribosomes in the presence and absence of EF-P, as well as eIF-5A in complex with the yeast 80S ribosome. Our structures suggest that stalling due to polyproline-stretches is due to destabilization of the P-site tRNA, which can even induce drop-off for short peptidyltRNAs. By contrast, the presence of EF-P or a/eIF-5A interacts and stabilizes the P- tRNA and positions the CCA-end with an optimal geometry for peptide bond formation. We identified rhamnoslyation as the modification present in EF-P proteins from γ-proteobacteria, such as Pseudomonas aeruginosa and Shewanella oneidensis. We characterized and structurally identified a new subfamily of EF-P in the phylum Actinobacteria, which includes the medically and economically important genera Corynebacterium, Mycobacterium and Streptomyces. This project paves the way for the development of tailored designer EF-Ps for various applications.

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