In every cell, all proteins are synthesized on the ribosome in a messenger-RNA dependent fashion. During the initial phase of protein synthesis, the ribosome is programmed with the messenger-RNA and the intiator fMet-tRNAfMet. Elongation Factor P (EF-P) is an essential protein that stimulates the formation of the first peptide bond. Our crystal structure of EF-P bound to the 70S ribosome suggests that EF-P stimulates the formation of the first peptide bond by properly positioning the initiator tRNA in the ribosome (Blaha et al., 2009).
During synthesis of the peptide chain, the ribosome cycles through a series of reactions. These reactions are assisted by two universal elongation factors, EF-Tu and EF-G. A third elongation factor, LepA, increases the accuracy and efficiency of protein synthesis by reversing the reaction catalyzed by EF-G. We have determined the crystal structure of LepA from Escherichia coli to a resolution of 2.8 Å. Based on both the high degree of sequence identity of LepA and EF-G as well as the cryo-electron microscopy structure of a complex of EF-G bound to the 70S ribosome, we have derived a model for the function of LepA on the ribosome. In this model, the positively-charged, C-terminal domain of LepA favors the initial state of the EF-G catalyzed reaction (Evans et al., 2008).
Historically, protein synthesis could only be dissected into individual steps with the help of antibiotics and inhibitors. We have determined many structures of inhibitors and antibiotics bound to the large ribosomal subunit. These structures explain not only the mechanism, but also the species selectivity (Schroeder et al., 2007) of protein synthesis inhibitors. By using genetically modified ribosomes from Haloarcula marismortui, we could explain how the binding affinity of antibiotics is impacted by mutations within (Tu et al., 2005) as well as far distant from their binding site on the ribosome (Blaha et al., 2008).
References
Blaha G.*, Stanley R.E.*, and Steitz, T.A. (2009). Formation of the first peptide bond: The structure of EF-P bound to the 70S ribosome. Science 325 966-970 (PubMed).
Blaha, G.*, Gurel, G., Schroeder, S.J.*, Moore, P.B., and Steiz, T.A. (2008). Mutations outside the anisomycin-binding site can make ribosomes drug-resistant. J. Mol. Biol. 389 146-156 (PubMed).
Evans, R.N., Blaha, G., Bailey, S., and Steitz, T.A. (2008). The structure of LepA, the ribosomal back translocase. Proc Natl Acad Sci U S A 105 4673-4678 (PubMed).
Schroeder, S.J.*, Blaha, G.*, Moore, P.B., and Steitz, T.A. (2007). The structures of antibiotics bound to the E site region of the 50S ribosomal subunit of Haloarcular marismortui: 13-deoxytedanolide and girodazol. J. Mol. Biol. 367 1471-1479 (PubMed).
Tu D.*, Blaha G.*, Moore, P.B., Steitz, T.A. (2005). Structure of MLSBK antibiotics bound to mutated large ribosomal subunits provide a structural explanation for resistance. Cell 121 257-270 (PubMed).
* These authors contributed equally to this work