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: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:The antibiotics chloramphenicol (CHL) and oxazolidinones including linezolid (LZD) are known to inhibit mitochondrial translation. This can result in serious, potentially deadly, side effects when used therapeutically. Although the mechanism by which CHL and LZD inhibit bacterial ribosomes has been elucidated in detail, their mechanism of action against mitochondrial ribosomes has yet to be explored. CHL and oxazolidinones bind to the ribosomal peptidyl transfer center (PTC) of the bacterial ribosome and prevent incorporation of incoming amino acids under specific sequence contexts, causing ribosomes to stall only at certain sequences. Through mitoribosome profiling, we show that inhibition of mitochondrial ribosomes is similarly context-specific – CHL and LZD lead to mitoribosome stalling primarily when there is an alanine, serine, or threonine in the penultimate position of the nascent peptide chain. Our findings could help inform the rational development of future, less mitotoxic, antibiotics, which are critically needed in the current era of increasing antimicrobial resistance.
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:Ribosomal RNA modifications are introduced by specific enzymes during ribosome assembly in bacteria. Deletion of individual modification enzymes has a minor effect on bacterial growth, ribosome biogenesis, and translation, which has complicated the definition of the function of the enzymes and their products. We have constructed an E. coli strain lacking 10 genes encoding enzymes that modify 23S rRNA around the peptidyl-transferase center. This strain exhibits severely compromised growth and ribosome assembly, especially at lower temperatures. Ribosomal protein composition of the mature 50S ribosomes and free 50S subunits was analyzed by SILAC based qMS approach. We have found that absence of 23S rRNA modifications around PTC does not affect significantly r-protein content of incompletely assembled 50S or mature 50S ribosomes.
Project description:Ribosomal RNA modifications are introduced by specific enzymes during ribosome assembly in bacteria. Deletion of individual modification enzymes has a minor effect on bacterial growth, ribosome biogenesis, and translation, which has complicated the definition of the function of the enzymes and their products. We have constructed an E. coli strain lacking 10 genes encoding enzymes that modify 23S rRNA around the peptidyl-transferase center. This strain exhibits severely compromised growth and ribosome assembly, especially at lower temperatures. Ribosomal protein composition of the mature 50S ribosomes and free 50S subunits was analyzed by SILAC based qMS approach. We have found that absence of 23S rRNA modifications around PTC does not affect significantly r-protein content of incompletely assembled 50S or mature 50S ribosomes.
Project description:Ribosomal RNA modifications are introduced during ribosome assembly by snoRNA and stand-alone modification enzyme based mechanisms in budding yeast. Lack of individual modifications in rRNA has a minor effect on yeast growth, ribosome biogenesis, and translation, which has complicated the definition of the biological function of rRNA modifications. We have constructed a S.cerevisiae strain lacking 7 25S rRNA modifications (Ψ2826, Um2921, Gm2619, m5C2870, Ψ2880, Um2724 and Gm2922)in peptidyl-transferase center. This strain exhibits severely compromised growth at 30°C, reduced level of global translation and actively translating ribosomes and cold sensitivity. Ribosomal protein composition of the mature 80S ribosomes was analyzed by SILAC based qMS approach. We have found that absence of PTC modifications around PTC does not affect significantly r-protein content of 80S ribosomes.
Project description:The prokaryotic translation elongation factor P (EF-P), and the eukaryotic/archeal counterparts eIF5A/aIF5A, are proteins that serve a crucial role in mitigating ribosomal stalling during the translation of specific sequences, notably those containing consecutive proline residues. Although mitochondrial DNA-encoded proteins synthesized by mitochondrial ribosomes also contain polyproline stretches, an EF-P/eIF5A mitochondrial counterpart remains unidentified. Here, we show that the missing factor is the translational activator of COX1 (TACO1), a protein causative of a juvenile form of neurodegenerative Leigh's syndrome associated with cytochrome c oxidase deficiency. By using a combination of metabolic labeling, puromycin release, and ribosome profiling experiments, we show that TACO1 is required for the rapid synthesis of the poly-proline rich COX1 and COX3 proteins, while its requirement is negligible for other proteins. In agreement with a role in translation rate regulation, we show that TACO1 cooperates with the N-terminal extension of the large ribosomal subunit bL27m to provide stability to the peptidyl-transferase center during elongation, and that excess TACO1 enhances overall translation rate. We conclude that TACO1 is a Translation Accelerator and propose it as a promising target to regulate mitochondrial protein synthesis in disease scenarios.
Project description:Impairment of ribosome function activates the MAPKKK ZAK, leading to activation of mitogen-activated protein (MAP) kinases p38 and JNK and inflammatory signaling. The mechanistic basis for activation of this ribotoxic stress response (RSR) re-mains completely obscure. We show that the long isoform of ZAK (ZAKα) directly associates with ribosomes by inserting its flexible C terminus into the ribosomal intersubunit space. Here, ZAKα binds helix14 of 18S ribosomal RNA (rRNA). An adjacent domainin ZAKa also probes the ribosome, and together, these sensor domains are critically required for RSR activation after inhibition of both the E-site, the peptidyl transferase center (PTC), and ribotoxinaction. Finally, we show that ablation of the RSR response leads to organismal phenotypes and decreased lifespan in the nematode Caenorhabditis elegans (C. elegans). Our findings yield mechanistic insight into how cells detect ribotoxic stress and provide experimental in vivo evidence for its physiological importance.
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.