Ribosomal fidelity

The kinetic mechanism of aminoacyl-tRNA selection demonstrates that the forward steps of EF-Tu GTPase activation and accommodation are crucial for high fidelity. How can this observation be explained on a structural level. Unfortunately, we have high-resolution structures only of the ribosome prior to A-site binding and of the tRNAs bound to the ribosome after accommodation. Of the intermediate states, only the low-resolution structure of a ternary complex EF-Tu—GTP—aminoacyl-tRNA stalled after GTP hydrolysis has been determined by cryo-EM (Figure These studies revealed that EF-Tu interacts with the... 

Proteins are synthesized by the ribosomal assembly in living organisms, details of which have been the subject of excellent recent reviews. The ribosome is a marvelously complex system of three large RNA molecules and over 50 proteins. This assembly translates the information from mRNA into protein sequence with a fidelity of one mistake per each 10" elongation cycles. ... 

The ribosome is actively involved in maintenance of translational fidelity... 

Mutants in ribosomal RNA that affect the fidelity of translation termination... 

Mutants in a ribosomal tunnel protein and in ribosome-bound chaperones affect translational fidelity... 

Masurekar et al. 1981). These observations established early on that the binding of small molecules to the ribosome could affect translational fidelity. Evidently, the ribosome was involved in translation beyond its catalytic activity. Over the last few decades, aminoglycosides have been instrumental in the elucidation of the decoding mechanism. 

Piepersberg W, Noseda V, Bock A (1979) Bacterial ribosomes with two ambiguity mutations effects of translational fidelity, on the response to aminoglycosides and on the rate of protein synthesis. Mol Gen Genet 171 23-34... 

Rodnina MV, Wintermeyer W (2001) EideUty of aminoacyl-tRNA selection on the ribosome kinetic and structural mechanisms. Annu Rev Biochem 70 415 35 Rodnina MV, Wintermeyer W (2001) Ribosome fidelity tRNA discrimination, proofreading and induced fit. Trends Biochem Sci 26 124—130... 

The aminoglycosides decrease the fidelity of translation by binding to the 30S subunit of the ribosome. This permits the formation of the peptide initiation complex but prohibits any subsequent addition of amino acids to the peptide. This effect is due to the inhibition of polymerization as well as to the failure of tRNA and mRNA codon recognition. Aminoglycosides are ototoxic (i.e., may produce partial deafness), damaging the auditory nerve. Kanamycin is less toxic. Since aminoglycosides are concentrated in the kidney, they may occasionally cause kidney damage. 

Proofreading by Aminoacyl-tRNA Synthetases The amino-acylation of tRNA accomplishes two ends (1) activation of an amino acid for peptide bond formation and (2) attachment of the amino acid to an adaptor tRNA that ensures appropriate placement of the amino acid in a growing polypeptide. The identity of the amino acid attached to a tRNA is not checked on the ribosome, so attachment of the correct amino acid to the tRNA is essential to the fidelity of protein synthesis. 

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