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A novel mechanism of bacteria to adapt to nutrient deprivation via the ribosome silencing factor RsfS (reference number: NMICROBIOL-19112987)

ABSTRACT: The factor RsfS is present in almost all bacteria and organelles. RsfS is important under conditions of nutrient downshifts leading to decreasing growth rates. A common feature of these conditions is a strong reduction of the translation capacity revealed by polysomal fraction decrease and a vast appearance of vacant 70S ribosomes, which might cause a devastating energy drain by stimulating the activity of GTPase proteins e.g. EF-G with idle ribosomes. Here we show that RsfS blocks association of free ribosomal subunits and induces dissociation exclusively of vacant ribosomes rather than of programmed ribosomes carrying tRNAs. As a consequence, RsfS reduces the abundance of the cellular translational apparatus, and the EF-G dependent burst of GTP cleavage in the presence of vacant 70S ribosomes as well as with 30S and 50S subunits is decreased. These observations hint to a regulatory role of RsfS by utilizing cellular resource in an economic way under conditions, where the amino acids are limited and energy has to be saved.

ORGANISM(S): Escherichia coli BW25113

PROVIDER: GSE142817 | GEO | 2022/08/22

REPOSITORIES: GEO

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Structure of Escherichia coli heat shock protein Hsp15 in complex with ribosomal 50S sununits bearing peptidyl-tRNA

Project description:In Escherichia coli, the heat shock protein 15 (Hsp15) is part of the cellular response to elevated temperature. Hsp15 interacts with peptidyl-tRNA-50S complexes that arise upon dissociation of translating 70S ribosomes, and is proposed to facilitate their rescue and recycling. A previous structure of E. coli Hsp15 in complex with peptidyl-tRNA-50S complex reported a binding site located at the central protuberance of the 50S subunit. By contrast, recent structures of RqcP, the Hsp15 homolog in Bacillus subtilis, in complex with peptidyl-tRNA-50S complexes have revealed a distinct site positioned between the anticodon-stem-loop (ASL) of the P-site tRNA and H69 of the 23S rRNA. Here we demonstrate that exposure of E. coli cells to heat shock leads to dissociation of 70S ribosomes and accumulation of 50S subunits, thus identifying a natural substrate for Hsp15 binding. Additionally, we have determined a cryo-EM reconstruction of the Hsp15-50S-peptidyl-tRNA complex isolated from heat shocked E. coli cells, revealing that Hsp15 binds to the 50S-peptidyl-tRNA complex analogously to its B. subtilis homolog RqcP. Collectively, our findings support a model where Hsp15 promotes access to the A-site for putative rescue factors to release the aberrant nascent polypeptide chain.

2022-11-15 | GSE216100 | GEO

Quantitative mass spectrometry analysis of 70S ribosomes from iSAT

Project description:The ribosome is one of the largest and the most complicated enzymes in cells, making up 25% of the bacterial cell’s dry mass, and is responsible for protein synthesis in all organisms on earth. In 2013, Jewett et al. reported an in vitro system named integrated rRNA synthesis, ribosome assembly, and translation (iSAT) reaction, which provided a defined system for ribosome biogenesis in a near-physiological environment.In this project, the r-protein composition in 30S and 50S ribosomeal subunits assembled in the iSAT reaction was quantified by mass spectrometry compared to 15N labeled 70S ribosomes.

2023-05-10 | PXD038716 | Pride

Grad-seq shines light on unrecognized RNA and protein complexes in the model bacterium Escherichia coli

Project description:Stable protein complexes, including those formed with RNA, are major building blocks of every living cell. Escherichia coli has been the leading organism with respect to global bacterial protein-protein networks. However, there has been no global census of RNA/protein complexes in this model species of microbiology. Here, we performed Grad-seq to establish an RNA/protein complexome, reconstructing sedimentation profiles in a glycerol gradient for ~85% of all E. coli transcripts and ~49% of the proteins. In presenting use cases for this resource to be exploited, we show that its stable association with 30S ribosomes gives the seemingly noncoding RNA RyeG of prophage origin away as an mRNA of a toxic small protein. Similarly, we show that the broadly conserved uncharacterized protein YggL is a 50S subunit factor in assembled 70S ribosomes. Overall, this study complements existing interactome resources for the primary model bacterium E. coli with valuable RNA/protein complexome information and should facilitate functional discovery in this and many related species.

2020-06-30 | GSE152974 | GEO

Structural basis of ribosomal 30S subunit degradation by RNase R

Project description:Protein synthesis is a major energy-consuming process of the cell, which requires controlled production and turnover of ribosomes. While the last years have seen major advances in our understanding of ribosome biogenesis, structural insight into the degradation of ribosomes has been lacking. Here we present native structures of two distinct small ribosomal 30S subunit degradation intermediates associated with the 3’ to 5’ exonuclease, RNase R. The structures reveal that RNase R binds initially to the 30S platform to facilitate degradation of the functionally important anti-Shine-Dalgarno sequence and decoding site helix 44. RNase R then encounters a roadblock when it reaches the neck region of the 30S, which is overcome by a major structural rearrangement of the 30S head, involving loss of ribosomal proteins. RNase R parallels this movement, relocating to the decoding site, by using its N-terminal helix-turn-helix domain as an anchor. In vitro degradation assays suggest that head rearrangement poses a major kinetic barrier for RNase R, but also that the enzyme alone is sufficient for complete 30S degradation. Collectively, our results provide a mechanistic basis for RNase R-mediated 30S degradation and reveal that RNase R targets orphaned 30S subunits using a dynamic anchored binding site switching mechanism.

2023-12-25 | GSE251701 | GEO

Ribosome protein composition in wt and 23S+5S rRNA ribosomes

Project description:The 120-nt long 5S rRNA, is an indispensable component of cytoplasmic ribosomes in all living organisms. The functions of 5S rRNA and the reasons for its evolutionary preservation as an independent molecule remain unclear. Here we used ribosome engineering to investigate whether maintaining 5S rRNA as an independent molecule is critical for ribosome function and cell survival. By fusing circularly permutated 5S rRNA (cp5S) with 23S rRNA and deleting all wild type 5S rRNA genes, we generated an Escherichia coli strain completely devoid of free 5S rRNA. Viability of the engineered cells demonstrates that autonomous 5S rRNA is not required for cell growth at 37°C and is unlikely to have essential functions outside the ribosome. The fully-assembled ribosomes carrying 23S-cp5S hybrid rRNA and lacking free 5S rRNA are highly active in translation. However, the engineered cells accumulate aberrant 50S subunits that are unable to form stable 70S ribosomes. Cryo-EM analysis revealed a dramatically malformed peptidyl transferase center in the misassembled 50S subunits. The results of our experiments argue that the key evolutionary force preserving the autonomous nature of the smallest rRNA is its role in ribosome biogenesis.

2020-06-18 | PXD019058 | Pride

Determinants of heat resistance in Escherichia coli AW1.7

2011-03-02 | GSE27607 | GEO

The Arabidopsis Protein CONSERVED ONLY IN THE GREEN LINEAGE20 is Required for Plastid 50S Ribosome Biogenesis

Project description:Biogenesis of plastid ribosomes is facilitated by auxiliary factors which process and modify ribosomal RNAs (rRNA) or are involved in ribosome assembly. In comparison to their bacterial and mitochondrial counterparts, the biogenesis of plastid ribosomes is less well understood and few auxiliary factors have been described so far. In this study, we report the functional characterization of CGL20 (CONSERVED ONLY IN THE GREEN LINEAGE20) in Arabidopsis thaliana (AtCGL20) a small, proline-rich protein which is targeted to mitochondria and chloroplasts. In Arabidopsis, CGL20 is encoded by segmentally duplicated genes of high similarity (AtCGL20A and AtCGL20B), and inactivation of both in the atcgl20ab mutant leads to a visible virescent phenotype, and growth arrest at low temperature. The chloroplast proteome, thylakoid complex abundance and pigment composition are significantly affected in atcgl20ab mutants, resulting in a combined proton gradient regulation (pgr) and chlororespiratory reduction (crr) phenotype. Loss of AtCGL20 alters plastid rRNA ratios, perturbs the formation of a hidden break in 23S rRNA and causes abnormal accumulation of 50S ribosomal subunits in the high-molecular-mass fraction of chloroplast stromal extracts. Moreover, AtCGL20A-eGFP fusion proteins comigrate with 50S ribosomal subunits in sucrose density gradients, even after RNase treatment of stromal extracts. Therefore, we propose that AtCGL20 participates in late stages of the biogenesis of 50S ribosomal subunits in plastids – a role which presumably evolved in the green lineage as a consequence of structural divergence of plastid ribosomes.

2020-03-16 | GSE134415 | GEO

Separation and Paired Proteome Profiling of Plant Chloroplast and Cytoplasmic Ribosomes

Project description:Conventional preparation methods of plant ribosomes fail to resolve non-translating chloroplast or cytoplasmic ribosome subunits from translating fractions. We established preparation of these ribosome complexes from Arabidopsis thaliana leaf, root, and seed tissues by optimized sucrose density gradient centrifugation of protease protected plant extracts. The method co-purified non-translating 30S and 40S ribosome subunits, separated non-translating 50S from 60S subunits, and resolved assembled monosomes from low oligomeric polysomes. Combining ribosome fractionation with microfluidic rRNA analysis and proteomics, we characterized the rRNA and ribosomal protein (RP) composition. The identity of cytoplasmic and chloroplast ribosome complexes and the presence of ribosome biogenesis factors in the 60S - 80S sedimentation interval were verified. In vivo cross-linking of leaf tissue stabilized ribosome biogenesis complexes but induced polysome run-off. Omitting cross-linking, the established paired fractionation and proteome analysis monitored relative abundances of plant chloroplast and cytoplasmic ribosome fractions and enabled analysis of RP composition and ribosome associated proteins including transiently associated biogenesis factors.

2021-09-09 | PXD019329 | Pride

Ribosome collisions in bacteria promote ribosome rescue by triggering mRNA cleavage by SmrB

Project description:Ribosome rescue pathways recycle stalled ribosomes and target problematic mRNAs and aborted proteins for degradation. In bacteria, it remains unclear how rescue pathways distinguish ribosomes stalled in the middle of a transcript from actively translating ribosomes. In a genetic screen in E. coli, we discovered a novel rescue factor that has endonuclease activity. SmrB cleaves mRNAs upstream of stalled ribosomes, allowing the ribosome rescue factor tmRNA (which acts on truncated mRNA) to rescue upstream ribosomes. SmrB is recruited by ribosome collisions. Cryo-EM structures of collided disomes from E. coli and B. subtilis reveal interactions between the 30S subunits and a possible SmrB binding site. These findings show that ribosome collisions trigger ribosome rescue in bacteria and reveal the mechanism by which this occurs.

2022-08-01 | GSE179691 | GEO

Determinants of heat resistance in Escherichia coli AW1.7

Project description:Microarray hybridization of cDNA libraries obtained from exponentially growing or heat-shocked AW1.7 or GGG10 cultures was performed to compare gene expression of these two strains. Expression of selected genes from different functional groups was quantified by quantitative PCR (q-PCR). DnaK, 30S and 50S risobomal subunits were overexpressed in E. coli GGG10 relative to E. coli AW1.7 upon heat shock at 50M-BM-0C, indicating improved ribosome stability. The outer membrane porin NmpC and several transport proteins were overexpressed in exponentially growing E. coli AW1.7. Gene expression of a heat resistant strain, E. coli AW1.7, was compared to gene expression in a heat sensitive strain, E coli GGG10. RNA was isolated from late exponential cultures, or from late exponential cells heat-shocked by exposure to 50M-BM-0C for 15 min. Three independent biological repeats were analyzed, and technical repeats (dye-swap) were performed for two of three biological repeats.

2011-03-02 | E-GEOD-27607 | biostudies-arrayexpress

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