Project description:Macrolides are clinically important antibiotics thought to inhibit bacterial growth by impeding the passage of newly synthesized polypeptides through the nascent peptide exit tunnel of the bacterial ribosome. Recent data challenged this view by showing that macrolide antibiotics can differentially affect synthesis of individual proteins. In order to understand the general mechanism of macrolide action, we used genome-wide ribosome profiling and analyzed the redistribution of ribosomes translating highly expressed genes in bacterial cells treated with high concentrations of macrolide antibiotics. The metagene analysis indicated that inhibition of early rounds of translation, which would be characteristic of the conventional view of macrolide action, occurs only at a limited number of genes. Translation of most genes proceeds past the 5' proximal codons and can be arrested at more distal codons when the ribosome encounters specific short sequence motifs. The sequence motifs enriched in the sites of arrest are confined to the nascent peptide residues in the peptidyl transferase center but not to the peptide segments that contact the antibiotic molecule in the exit tunnel. This led to the conclusion that the general mode of macrolide action involves selective inhibition of peptide bond formation between specific combinations of donor and acceptor substrates. Additional factors operating in the living cell but not during in vitro protein synthesis may modulate site-specific action of macrolide antibiotics. Comparing ribosome distribution in bacterial cells treated with macrolide antibiotics against the control cells.
Project description:Macrolides are clinically important antibiotics thought to inhibit bacterial growth by impeding the passage of newly synthesized polypeptides through the nascent peptide exit tunnel of the bacterial ribosome. Recent data challenged this view by showing that macrolide antibiotics can differentially affect synthesis of individual proteins. In order to understand the general mechanism of macrolide action, we used genome-wide ribosome profiling and analyzed the redistribution of ribosomes translating highly expressed genes in bacterial cells treated with high concentrations of macrolide antibiotics. The metagene analysis indicated that inhibition of early rounds of translation, which would be characteristic of the conventional view of macrolide action, occurs only at a limited number of genes. Translation of most genes proceeds past the 5' proximal codons and can be arrested at more distal codons when the ribosome encounters specific short sequence motifs. The sequence motifs enriched in the sites of arrest are confined to the nascent peptide residues in the peptidyl transferase center but not to the peptide segments that contact the antibiotic molecule in the exit tunnel. This led to the conclusion that the general mode of macrolide action involves selective inhibition of peptide bond formation between specific combinations of donor and acceptor substrates. Additional factors operating in the living cell but not during in vitro protein synthesis may modulate site-specific action of macrolide antibiotics.
Project description:We report the context-specific activity of two peptidyl transferase targeting antibiotics, chloramphenicol and linezolid. By generating ribosome profiling data in the presence or absence of either chloramphenicol or linezolid we mapped the relative change of ribosome density induced by these antibiotics. We find that both inhibitors preferentially arrest ribosomes that carry either an alanine, serine, or threonine in the penultimate (-1) position of the nascent peptide chain. Additionally ribosomes that carry a glycine in either the P site (0) or A-site (+1) counteract the inhibitory activity of both inhibitors. The context-specific action of chloramphenicol illuminates the operation of the mechanism of inducible resistance that relies on programmed drug-induced translation arrest. In addition, our findings expose the functional interplay between the nascent chain and the peptidyl transferase center.
Project description:Campylobacter jejuni is a major zoonotic pathogen transmitted to humans via the food chain. C. jejuni is prevalent in chickens, a natural reservoir for this pathogenic organism. Due to the importance of macrolide antibiotics in clinical therapy of human campylobacteriosis, development of macrolide resistance in Campylobacter has become a concern for public health.To facilitate understanding the molecular basis associated with the fitness difference between Erys and Eryr Campylobacter, we compared the transcriptomes between ATCC 700819 and its isogenic Eryr transformant T.L.101 using DNA microarray.
Project description:Campylobacter jejuni is a major zoonotic pathogen transmitted to humans via the food chain. C. jejuni is prevalent in chickens, a natural reservoir for this pathogenic organism. Due to the importance of macrolide antibiotics in clinical therapy of human campylobacteriosis, development of macrolide resistance in Campylobacter has become a concern for public health.To facilitate understanding the molecular basis associated with the fitness difference between Erys and Eryr Campylobacter, we compared the transcriptomes between ATCC 700819 and its isogenic Eryr transformant T.L.101 using DNA microarray. The design utilized an available two color microarray slide for the entire transcriptome of Campylobacter jejuni. Four hybridizations were performed each with independently extracted samples of either macrolide susceptible ATCC 700819 cDNA samples or its isogenic Eryr transformant T.L.101 cDNA samples. A dye swap was utilized to help minimize dye dependent bias. Thus, there were four biological replicates of each sample.
Project description:RNA-seq based transcriptome profiling allows a detailed molecular analysis of the E.coli transcriptome (~4200 genes) after perturbation with different antibiotics. Transcriptome fingerprints enable the identification of gene and pathway level responses to treatment to derive a mechanistic understanding of antibiotics mode of action and to differentiate antibiotics. For this goal, treatment has to be performed in a short time period and with sublethal concentrations of the antibiotics. Sublethal concentrations were chosen based on the EC90 concentration of the antibiotic necessary to change the cellular morphology compared to control conditions. Conclusions: Our study represents the first detailed analysis of E.coli transcriptomes after treatment with different antibiotics, with biologic replicates, generated by RNA-seq technology. The experimental design and data analysis reported here should provide a framework for comparative investigations of expression profiles of known and novel antibiotics. We conclude that RNA-seq based transcriptome characterization would expedite genetic network analyses and permit the dissection of complex biologic functions.
Project description:Antibiotics of the orthosomycin class bind at a distinct site on the large subunit of the bacterial ribosome not used by any other known protein synthesis inhibitor. Structural and biochemical in vitro studies suggested that orthosomycins should block accommodation of aminoacyl-tRNAs in the ribosomal A-site arresting the ribosome at the start codons of the genes. However, the mode of action of orthosomycins in the living cell remains unknown. Here, to get a general and unbiased view of the mode of action of orthosomycin antibiotics, we carried out genome-wide ribosome profiling analysis in Escherichia coli cells exposed to evernimicin, one of the most active antibiotics of this class. Our in vivo data, supported by the analysis of evernimicin action upon in vitro translation of a variety of mRNAs, argue that orthosomycins preferentially inhibit translation elongation and act in a context specific manner. We show that evernimicin predominantly arrests translation when the ribosome needs to accommodate Pro-tRNA or Leu-tRNA in the A site while polymerizing specific amino acid sequences. We further show that the discovered context specificity of orthosomycins is exploited for the programmed translation arrest that apparently regulates resistance to these antibiotics.