Substrate-assisted catalysis of peptide bond formation by the ribosome

The ribosome accelerates the rate of peptide bond formation by at least 10⁷-fold, but the catalytic mechanism remains controversial. Here we report evidence that a functional group on one of the tRNA substrates plays an essential catalytic role in the reaction. Substitution of the P-site tRNA A76 2′ OH with 2′ H or 2′ F results in at least a 10 ⁶-fold reduction in the rate of peptide bond formation, but does not affect binding of the modified substrates. Such substrate-assisted catalysis is relatively uncommon among modern protein enzymes, but it is a property predicted to be essential for the evolution of enzymatic function. These results suggest that substrate assistance has been retained as a catalytic strategy during the evolution of the prebiotic peptidyl transferase center into the modern ribosome.