An intact ribose moiety at A2602 of 23S rRNA is key to trigger peptidyl-tRNA hydrolysis during translation termination

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Abstract
Peptide bond formation and peptidyl-tRNA hydrolysis are the two elementary chemical reactions of protein synthesis catalyzed by the ribosomal peptidyl transferase ribozyme. Due to the combined effort of structural and biochemical studies, details of the peptidyl transfer reaction have become increasingly clearer. However, significantly less is known about the molecular events that lead to peptidyl-tRNA hydrolysis at the termination phase of translation. Here we have applied a recently introduced experimental system, which allows the ribosomal peptidyl transferase center (PTC) to be chemically engineered by the introduction of non-natural nucleoside analogs. By this approach single functional group modifications are incorporated, thus allowing their functional contributions in the PTC to be unravelled with improved precision. We show that an intact ribose sugar at the 23S rRNA residue A2602 is crucial for efficient peptidyl-tRNA hydrolysis, while having no apparent functional relevance for transpeptidation. Despite the fact that all investigated active site residues are universally conserved, the removal of the complete nucleobase or the ribose 2′-hydroxyl at A2602, U2585, U2506, A2451 or C2063 has no or only marginal inhibitory effects on the overall rate of peptidyl-tRNA hydrolysis. These findings underscore the exceptional functional importance of the ribose moiety at A2602 for triggering peptide release.