Evolution of robustness to protein mistranslation by accelerated protein turnover
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ABSTRACT: To investigate how organisms mitigate the deleterious effects of mistranslation during evolution, a mutant tRNA was expressed in S. cerevisiae. The expression of Candida Ser-tRNACAG from a low copy plasmid in S. cerevisiae promoted mistranslation events by random incorporation of both serine and leucine at CUG codons. As mistranslation causes an overload of the protein quality pathways, it disrupts cellular protein homeostasis leading to a major fall in fitness. Laboratory evolutionary experiments were performed to study whether the fitness cost of mistranslation can be lowered. We also wanted to identify the cost-reduction strategy: reducing the frequencies of errors (mitigation), or increasing tolerance to errors (robustness), either by global or local activities.
Project description:To investigate how organisms mitigate the deleterious effects of mistranslation during evolution, a mutant tRNA was expressed in S. cerevisiae. The expression of Candida Ser-tRNACAG from a low copy plasmid in S. cerevisiae promoted mistranslation events by random incorporation of both serine and leucine at CUG codons. As mistranslation causes an overload of the protein quality pathways, it disrupts cellular protein homeostasis leading to a major fall in fitness. Laboratory evolutionary experiments were performed to study whether the fitness cost of mistranslation can be lowered. We also wanted to identify the cost-reduction strategy: reducing the frequencies of errors (mitigation), or increasing tolerance to errors (robustness), either by global or local activities. Gene expression was measured in the ancestor (non-evolved) lineage in two different situations: 1) carrying an empty vector and 2) expressing the mutant Ser-tRNACAG. Gene expression was also measured in three ambiguously evolved lineages (B3, D11, H9) in both situations (carrying an empty vector and expressing the mutant tRNA). Three independent experiments were performed for each lineage. Non-evolved strain with empty vector was used as control sample.
Project description:The leucine CUG codon was reassigned to serine in the fungal pathogen Candida albicans. To clarify the biological role of this tuneable codon ambiguity on drug resistance, we evolved C. albicans strains that were engineered to mistranslate the CUG codon at constitutively elevated levels, in the presence and absence of the antifungal drug fluconazole. Elevated levels of mistranslation resulted in the rapid acquisition of resistance to fluconazole.
Project description:Aminoacyl-tRNA synthetases (aaRSs) are essential enzymes that support robust and accurate protein synthesis. A rapidly expanding number of studies show that mutations in aaRSs lead to multiple human diseases, including neurological disorders and cancer. Much remains unknown about how aaRS mutations impact human health. In particular, how aminoacylation errors affect stress responses and fitness in eukaryotic cells remains poorly understood. The integrated stress response (ISR) is an adaptive mechanism in response to multiple stresses. However, chronic activation of the ISR contributes to the development of multiple diseases (e.g., neuropathies). Here we show that Ser misincorporation into Ala and Thr codons, resulting from aaRS editing defects or mutations in tRNAs, constitutively active the ISR. Such activation does not appear to depend on the accumulation of uncharged tRNAs, implicating that Ser mistranslation may lead to ribosome stalling and collision.
Project description:Mistranslation describes the misincorporation of an amino acid into a nascent polypeptide. Mistranslation has diverse effects on multicellular eukaryotes and is implicated in several human diseases. We introduced a mistranslating serine transfer RNA (tRNA) into Drosophila melanogaster that misincorporates serine at proline codons and found that it affected male and female flies differently. Here, we compare the transcriptomic response of male and female flies to mistranslation to identify cellular pathways that underlie this sex-specific response. Both males and females downregulated genes associated with metabolism in response to proline-to-serine mistranslation. Only males downregulated genes associated with developmental processes and response to negative stimuli such as infection, whereas only females downregulated aerobic respiration and ATP synthesis genes. Both sexes upregulated genes associated with gametogenesis but females upregulated cell cycle and DNA maintenance genes, suggesting that mistranslation may compromise genome integrity in females. This transcriptomic analysis advances our understanding of how males and females respond to mistranslation and has important implications for future studies that examine the influence of mistranslation on disease.
Project description:Translational errors occur at high rates, and they influence organism viability and the onset of genetic diseases. To investigate how organisms mitigate the deleterious effects of protein synthesis errors during evolution, a mutant yeast strain was engineered to translate a codon ambiguously (mistranslation). It thereby overloads the protein quality-control pathways and disrupts cellular protein homeostasis. This strain was used to study the capacity of the yeast genome to compensate the deleterious effects of protein mistranslation. Laboratory evolutionary experiments revealed that fitness loss due to mistranslation can rapidly be mitigated. Genomic analysis demonstrated that adaptation was primarily mediated by large-scale chromosomal duplication and deletion events, suggesting that errors during protein synthesis promote the evolution of genome architecture. By altering the dosages of numerous, functionally related proteins simultaneously, these genetic changes introduced large phenotypic leaps that enabled rapid adaptation to mistranslation. Evolution increased the level of tolerance to mistranslation through acceleration of ubiquitin-proteasome-mediated protein degradation and protein synthesis. As a consequence of rapid elimination of erroneous protein products, evolution reduced the extent of toxic protein aggregation in mistranslating cells. However, there was a strong evolutionary trade-off between adaptation to mistranslation and survival upon starvation: the evolved lines showed fitness defects and impaired capacity to degrade mature ribosomes upon nutrient limitation. Moreover, as a response to an enhanced energy demand of accelerated protein turnover, the evolved lines exhibited increased glucose uptake by selective duplication of hexose transporter genes. We conclude that adjustment of proteome homeostasis to mistranslation evolves rapidly, but this adaptation has several side effects on cellular physiology. Our work also indicates that translational fidelity and the ubiquitin-proteasome system are functionally linked to each other and may, therefore, co-evolve in nature.
Project description:<p>Translation fidelity is the limiting factor in the accuracy of gene expression. With an estimated frequency of 10-4, errors in mRNA decoding occur in a mostly stochastic manner. Little is known about the response of higher eukaryotes to chronic loss of ribosomal accuracy as per an increase in the random error rate of mRNA decoding. Here, we present a global and comprehensive picture of the cellular changes in response to translational accuracy in mammalian ribosomes impaired by genetic manipulation. In addition to affecting established protein quality control pathways, such as elevated transcript levels for cytosolic chaperones, activation of the ubiquitin-proteasome system, and translational slowdown, ribosomal mistranslation led to unexpected responses. In particular, we observed increased mitochondrial biogenesis associated with import of misfolded proteins into the mitochondria and silencing of the unfolded protein response in the endoplasmic reticulum.</p><p><br></p><p>This study describes the metabolomic analysis of HEK293 cells lines expressing mutant ribosomal protein RPS2 (human A226Y). RPS2 A226Y mutation has been shown to cause misreading and readthrough. Results provide insight into the response to chronic mistranslation in mammalian cells.</p>
Project description:Analysis of HEK293 cells lines expressing mutant ribosomal protein RPS2 (human A226Y). RPS2 A226Y mutation has been shown to cause misreading and readthrough. Results provide insight into the response to chronic mistranslation in mammalian cells.
Project description:Transcriptome analysis in cells after 20 hours of mistranslation induction in relation to control cells at the same time point where mistranslation was not induced (without the inducible tRNA construction)
Project description:The correct coupling of amino acids with transfer RNAs (tRNAs) is vital for translating genetic information into functional proteins. Errors during this process lead to mistranslation, where a codon is translated using the wrong amino acid. While unregulated and prolonged mistranslation is often toxic, growing evidence suggests that organisms, from bacteria to humans, can induce and use mistranslation as a mechanism to overcome unfavorable environmental conditions. Most known cases of mistranslation are caused by translation factors with poor substrate specificity or when substrate discrimination is sensitive to molecular changes such as mutations or post-translational modifications. Here we report two novel families of tRNAs, encoded by bacteria from the Streptomyces and Kitasatospora genera, that adopted dual identities by integrating the anticodons AUU (for Asn) or AGU (for Thr) into the structure of a distinct proline tRNA. These tRNAs are typically encoded next to a full-length or truncated version of a distinct isoform of bacterial-type prolyl-tRNA synthetase. Using two protein reporters, we showed that these tRNAs translate asparagine and threonine codons with proline. Moreover, when expressed in Escherichia coli, the tRNAs cause varying growth defects due to global Asn-to-Pro and Thr-to-Pro mutations. Yet, proteome-wide substitutions of Asn with Pro induced by tRNA expression increased cell tolerance to the antibiotic carbenicillin, indicating that Pro mistranslation can be beneficial under certain conditions. Collectively, our results significantly expand the catalog of organisms known to possess dedicated mistranslation machinery and provide support for the concept that mistranslation is a mechanism for cellular resiliency against environmental stress.