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Isolation of Translating Ribosomes Containing Peptidyl-tRNAs for Functional and Structural Analyses
Published on: February 25, 2011
pH-dependent conformational flexibility within the ribosomal peptidyl transferase center
1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, USA.
Summary
Dimethylsulfate modification of ribosomal adenosine A2451 does not support its role as a general acid-base catalyst in peptide bond formation. Instead, pH-dependent structural flexibility within the peptidyl transferase center is suggested.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- The universally conserved adenosine A2451 in the ribosomal peptidyl transferase center is proposed to catalyze peptide bond formation.
- Previous studies using pH-dependent dimethylsulfate (DMS) modification in Escherichia coli ribosomes suggested A2451 acts as a general acid-base catalyst with a pKa near neutrality.
Purpose of the Study:
- To investigate the role of A2451 in ribosomal catalysis.
- To re-evaluate the interpretation of pH-dependent DMS modification data regarding A2451's catalytic function.
Main Methods:
- Comparative analysis of pH-dependent DMS modification in ribosomes from Haloarcula marismortui (archaea) and Saccharomyces cerevisiae (yeast).
- Analysis of A2451 modification site (N1 vs. N3 imino group) in E. coli ribosomes using Dimroth rearrangement assays.
- Structural analysis based on the 50S ribosomal crystal structure.
Main Results:
- A2451 in H. marismortui ribosomes showed an inverted pH profile, inconsistent with proton-mediated base protection.
- In S. cerevisiae ribosomes, C2452, not A2451, was modified in a pH-dependent manner.
- DMS modification in E. coli ribosomes likely occurred at the N1 imino group of A2451, a solvent-inaccessible site without structural rearrangement.
Conclusions:
- pH-dependent DMS modification of A2451 does not provide evidence for or against a general acid-base catalytic role in protein synthesis.
- The data suggest pH-dependent conformational flexibility within the ribosomal peptidyl transferase center.
- The precise nature and physiological significance of this conformational flexibility remain unknown.
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