Formation of the First Peptide Bond: The Structure of EF-P Bound to the 70S Ribosome

Elongation factor P (EF-P) is an essential protein that stimulates the formation of the first peptide bond in protein synthesis. Here we report the crystal structure of EF-P bound to the Thermus thermophilus 70S ribosome along with the initiator transfer RNA N-formyl-methionyl-tRNA(i) (fMet-tRNA(i)(fMet)) and a short piece of messenger RNA (mRNA) at a resolution of 3.5 angstroms. EF-P binds to a site located between the binding site for the peptidyl tRNA (P site) and the exiting tRNA (E site). It spans both ribosomal subunits with its amino terminal domain positioned adjacent to the aminoacyl acceptor stem and its carboxyl terminal domain positioned next to the anticodon stem-loop of the P site-bound initiator tRNA. Domain II of EF-P interacts with the ribosomal protein L1, which results in the largest movement of the L1 stalk that has been observed in the absence of ratcheting of the ribosomal subunits. EF-P facilitates the proper positioning of the fMet-tRNA(i)(fMet) for the formation of the first peptide bond during translation initiation.