Project description:We use ribosome profiling to demonstrate the selectivity of a small molecule, PF-06446846 that inhibits translation of its target by selectively inducing ribosome-stalling in a nascent chain sequence dependent manner.
Project description:We use ribosome profiling to compare the selectivity of two small molecules, PF-06446846 and PF-06378503 that inhibits translation of their target by selectively inducing ribosome-stalling in a nascent chain sequence dependent manner.
Project description:Folding newly synthesized proteins relies on the ribosome intricately coordinating mRNA translation with a network of ribosome-associated machinery. The principles that drive the coordination of this diverse machinery remain poorly understood. Here, we use selective ribosome profiling to determine how the essential chaperonin TRiC/CCT and the Hsp70 Ssb are recruited to ribosome-nascent chain complexes to mediate cotranslational protein folding. Whereas substrate localization and nascent chain sequence are the major determinants of cotranslational recruitment of Ssb, we found that temporal and structural elements drive TRiC engagement. For both chaperones, however, local slowdowns in translation enhance chaperone enrichment. This work helps define the principles that dictate the coordinated activity of ribosome-associated factors to perform their critical role in maintaining a properly folded nascent proteome.
Project description:Human genetics as well as pharmacological intervention reveal that Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) plays a key role in regulating the levels of plasma low density lipoprotein cholesterol (LDL-C). Here we demonstrate that the compound PF-06446846 inhibits translation of PCSK9 by stalling the ribosome near codon 34 of its messenger RNA. Inhibition by PF-06446846 is sensitive to the amino acid sequence of the PCSK9 nascent chain, and not the messenger RNA. PF-06446846 also reduces plasma PCSK9 and total cholesterol levels in rats following oral dosing. Using ribosome profiling to examine the proteome-wide effects of PF-06446846, we find that it is exceptionally specific for PCSK9 and has no measurable effect on 99.7% of the translatome at concentrations sufficient for 90% inhibition of PCSK9 expression. Together, PF-06446846 represents the first example of an orally administered small molecule directly targeting PCSK9 that functions by a mechanism inhibiting translation during elongation with a high degree of selectivity. Selective inhibition of translation in human may represent a new approach to target proteins with small molecules.
Project description:Human genetics as well as pharmacological intervention reveal that Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) plays a key role in regulating the levels of plasma low density lipoprotein cholesterol (LDL-C). Here we demonstrate that the compound PF-06446846 inhibits translation of PCSK9 by stalling the ribosome near codon 34 of its messenger RNA. Inhibition by PF-06446846 is sensitive to the amino acid sequence of the PCSK9 nascent chain, and not the messenger RNA. PF-06446846 also reduces plasma PCSK9 and total cholesterol levels in rats following oral dosing. Using ribosome profiling to examine the proteome-wide effects of PF-06446846, we find that it is exceptionally specific for PCSK9 and has no measurable effect on 99.7% of the translatome at concentrations sufficient for 90% inhibition of PCSK9 expression. Together, PF-06446846 represents the first example of an orally administered small molecule directly targeting PCSK9 that functions by a mechanism inhibiting translation during elongation with a high degree of selectivity. Selective inhibition of translation in human may represent a new approach to target proteins with small molecules.
Project description:The ribosome collision due to translational stalling is recognized as a problematic event in translation by E3 ubiquitin ligase Hel2, leading to the non-canonical subunit dissociation followed by targeting of the faulty nascent peptides for degradation. Although Hel2-mediated quality control greatly contributes to maintaining cellular protein homeostasis, its physiological role in dealing with endogenous substrates remains unclear. Here we present a genome-wide analysis, based on selective ribosome profiling, to survey the endogenous substrates for Hel2. This reveals that Hel2 preferentially binds to the pre-engaged secretory ribosome-nascent-chain complexes (RNCs), which is translating upstream of targeting signals. Notably, Hel2 recruitment into secretory RNCs is elevated in the SRP-deficient condition; furthermore, the mitochondrial defects caused by insufficient SRP are enhanced by hel2 deletion, together with the mistargeting of secretory proteins into mitochondria. Collectively, our findings provide novel insights into the risk management in the secretory pathway for maintaining the cellular protein homeostasis.
Project description:The yeast Hsp70 chaperone Ssb interacts with ribosomes and nascent chains to co-translationally assist protein folding. Here, we present a proteome-wide analysis of Hsp70 function during translation, based on in vivo selective ribosome profiling, that reveals mechanistic principles coordinating translation with chaperone-assisted protein folding. Ssb binds most cytosolic, nuclear, and mitochondrial proteins and a subset of ER proteins, supporting its general chaperone function. Position-resolved analysis of Ssb engagement reveals compartment- and protein-specific nascent chain binding profiles that are coordinated by emergence of positively charged peptide stretches enriched in aromatic amino acids. Ssbs’ function is temporally coordinated by RAC but independent from NAC. Analysis of ribosome footprint densities along orfs reveals that ribosomes translate faster at times of Ssb binding. This is coordinated by biases in mRNA secondary structure, and codon usage as well as the action of Ssb, suggesting chaperones may allow higher protein synthesis rates by actively coordinating protein synthesis with co-translational folding.
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:Mitochondria contain a specific translation machinery for the synthesis of respiratory chain components encoded on the mitochondrial genome. Mitochondrial tRNAs (mt-tRNAs) are also generated from the mitochondrial genome and, similar to their cytoplasmic counterparts, are modified at various positions. Here, we find that the RNA methyltransferase METTL8, is a mitochondrial protein that facilitates m3C methylation at position C32 of mt-tRNASer(UCN) and mt-tRNAThr. METTL8 knock out cells show reduced and over expressing cells enhanced respiratory chain activity. In pancreatic cancer, METTL8 levels are high, which correlates with patient survival. Indeed, METTL8 up regulation stimulates respiratory chain activity in these cells. Ribosome occupancy analysis using ribosome profiling revealed ribosome stalling on mt-tRNASer(UCN) and mt-tRNAThr codons and mass spectrometry analysis of native ribosomal subcomplexes unraveled reduced respiratory chain incorporation of the mitochondria encoded proteins ND6 and ND1. A well-balanced translation of mt-tRNASer(UCN) and mt-tRNAThr codons through METTL8-mediated C32 methylation might therefore provide optimal respiratory chain compositions and function.
Project description:As nascent polypeptides exit ribosomes, they are engaged by a series of processing, targeting and folding factors. Here we present a selective ribosome profiling strategy that enables global monitoring of when these factors engage polypeptides in the complex cellular environment. Studies of the Escherichia coli chaperone Trigger Factor (TF) reveal that, while TF can interact with many polypeptides, β-barrel outer membrane proteins are the most prominent substrates. Loss of TF leads to broad outer membrane defects and premature, cotranslational protein translocation. While in vitro studies suggested that TF is prebound to ribosomes waiting for polypeptides to emerge from the exit channel, we find that in vivo TF engages ribosomes only after ~100 amino acids are translated. Moreover, excess TF interferes with cotranslational removal of the N-terminal formyl methionine. Our studies support a triaging model in which proper protein biogenesis relies on the fine-tuned, sequential engagement of processing, targeting ad folding factors. Examination of translation in the Gram-negative bacterium Escherichia coli, as well as an analysis of the interactions between nascent chains and the molecular chaperone Trigger Factor.