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The ribosome as an entropy trap
Annette Sievers1, Malte Beringer, Marina V Rodnina
1Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA.
Summary
The ribosome significantly accelerates peptide bond formation by 20 million-fold, primarily by reducing entropy, not enthalpy. This suggests substrate positioning and water exclusion, rather than chemical catalysis, are key to its function.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- The ribosome is a complex molecular machine responsible for protein synthesis.
- Understanding the catalytic mechanism of the ribosome is crucial for deciphering protein production.
- Enzymes typically lower activation enthalpy; the ribosome's mechanism may differ.
Purpose of the Study:
- To investigate the catalytic effectiveness of the ribosome in peptide bond formation.
- To compare the ribosome's catalytic mechanism with uncatalyzed reactions.
- To elucidate the role of activation parameters in ribosomal catalysis.
Main Methods:
- Compared the rate of uncatalyzed peptide bond formation with ribosomal peptidyl transfer.
- Determined activation parameters (enthalpy and entropy) for both reactions.
- Analyzed the temperature dependence of second-order rate constants.
Main Results:
- The ribosome enhances peptide bond formation rate by 2 x 10(7)-fold.
- Ribosomal catalysis shows a less favorable enthalpy of activation compared to solution-phase reactions.
- The rate enhancement is solely attributed to a significant reduction in the entropy of activation.
Conclusions:
- The ribosome's catalytic power stems from entropy reduction, not favorable enthalpy changes.
- Ribosomal catalysis likely involves precise substrate positioning and/or water exclusion within the active site.
- These findings challenge conventional chemical catalysis models for the ribosome, supporting a physical mechanism.