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Functional consequences of binding macrolides to ribosomes
Abstract:
Macrolide antibiotics bind to the large subunit of procaryotic ribosomes and perturb protein synthesis. There are two competing models to explain this perturbation: (1) shortly after initiation of the polypeptide chain, peptide bond formation and/or translocation is inhibited by the presence of macrolides that are bound in the ribosome 'tunnel' through which the nascent peptide travels; (2) bound macrolides loosen the interaction between the ribosome and peptidyl-tRNA, which therefore, dissociates with a higher probability. The former view cannot easily explain the observed enhancement by macrolides of the dissociation of peptidyl-tRNAs from ribosomes, while the latter view is consistent with the available data. Peptidyl-tRNAs are bound to ribosomes through non-specific and decoding-specific interactions. If macrolides preferentially weaken the non-specific interactions, a greater fraction of the binding energy will be due to decoding-specific interactions and better discrimination between erroneous and correct peptidyl-tRNAs should result. This idea has been tested with low doses of erythromycin, which was observed to counteract the error-inducing effects of streptomycin and of ethanol on the synthesis of beta-galactosidase by Escherichia coli. A specific error near the C-terminus of the enzyme was also responsive to this effect of erythromycin, which therefore must have exerted its influence long after the initiation of the polypeptide synthesis. These results are more easily explained by the idea that the primary mechanism of inhibition of protein synthesis by macrolides is to stimulate the dissociation of peptidyl-tRNA from the ribosome.
Insights
Macrolide antibiotics inhibit protein synthesis by causing peptidyl-tRNAs to dissociate from ribosomes. This mechanism explains how macrolides like erythromycin reduce errors during bacterial protein production.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Macrolide antibiotics target the large ribosomal subunit in prokaryotes, affecting protein synthesis.
- Two models exist: inhibition of peptide bond formation/translocation within the ribosomal tunnel, or destabilization of peptidyl-tRNA leading to dissociation.
- The latter model better explains macrolide-induced peptidyl-tRNA dissociation.
Purpose of the Study:
- To investigate the mechanism by which macrolide antibiotics perturb protein synthesis.
- To determine if macrolides primarily inhibit peptide synthesis or promote peptidyl-tRNA dissociation.
- To test the hypothesis that macrolides weaken non-specific peptidyl-tRNA interactions, enhancing decoding fidelity.
Main Methods:
- Utilized low doses of erythromycin in Escherichia coli protein synthesis experiments.
- Assessed the effects of erythromycin on the synthesis of beta-galactosidase.
- Examined the influence of erythromycin on errors induced by streptomycin and ethanol.
Main Results:
- Erythromycin counteracted error-inducing effects of streptomycin and ethanol during beta-galactosidase synthesis.
- The observed error reduction occurred late in polypeptide synthesis, near the C-terminus.
- Results support the model where macrolides enhance peptidyl-tRNA dissociation.
Conclusions:
- The primary mechanism of macrolide antibiotic action is the stimulation of peptidyl-tRNA dissociation from the ribosome.
- This dissociation mechanism explains the observed reduction in protein synthesis errors.
- Macrolides may enhance the discrimination between correct and erroneous peptidyl-tRNAs by weakening non-specific binding.