1
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Mattingly JM, Nguyen HA, Roy B, Fredrick K, Dunham CM. Structural analysis of noncanonical translation initiation complexes. J Biol Chem 2024; 300:107743. [PMID: 39222680 PMCID: PMC11497404 DOI: 10.1016/j.jbc.2024.107743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2024] [Revised: 08/14/2024] [Accepted: 08/23/2024] [Indexed: 09/04/2024] Open
Abstract
Translation initiation is a highly regulated, multi-step process that is critical for efficient and accurate protein synthesis. In bacteria, initiation begins when mRNA, initiation factors, and a dedicated initiator fMet-tRNAfMet bind the small (30S) ribosomal subunit. Specific binding of fMet-tRNAfMet in the peptidyl (P) site is mediated by the inspection of the fMet moiety by initiation factor IF2 and of three conserved G-C base pairs in the tRNA anticodon stem by the 30S head domain. Tandem A-minor interactions form between 16S ribosomal RNA nucleotides A1339 and G1338 and tRNA base pairs G30-C40 and G29-C41, respectively. Swapping the G30-C40 pair of tRNAfMet with C-G (called tRNAfMet M1) reduces discrimination against the noncanonical start codon CUG in vitro, suggesting crosstalk between the gripping of the anticodon stem and recognition of the start codon. Here, we solved electron cryomicroscopy structures of Escherichia coli 70S initiation complexes containing the fMet-tRNAfMet M1 variant paired to the noncanonical CUG start codon, in the presence or absence of IF2 and the non-hydrolyzable GTP analog GDPCP, alongside structures of 70S initiation complexes containing this tRNAfMet variant paired to the canonical bacterial start codons AUG, GUG, and UUG. We find that the M1 mutation weakens A-minor interactions between tRNAfMet and 16S nucleotides A1339 and G1338, with IF2 strengthening the interaction of G1338 with the tRNA minor groove. These structures suggest how even slight changes to the recognition of the fMet-tRNAfMet anticodon stem by the ribosome can impact the start codon selection.
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MESH Headings
- Escherichia coli/metabolism
- Escherichia coli/genetics
- RNA, Transfer, Met/metabolism
- RNA, Transfer, Met/chemistry
- RNA, Transfer, Met/genetics
- Peptide Chain Initiation, Translational
- Cryoelectron Microscopy
- Escherichia coli Proteins/metabolism
- Escherichia coli Proteins/chemistry
- Escherichia coli Proteins/genetics
- Anticodon/metabolism
- Anticodon/chemistry
- Codon, Initiator/metabolism
- Ribosome Subunits, Small, Bacterial/metabolism
- Ribosome Subunits, Small, Bacterial/chemistry
- RNA, Ribosomal, 16S/metabolism
- RNA, Ribosomal, 16S/chemistry
- RNA, Ribosomal, 16S/genetics
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2
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Gemler BT, Warner BR, Bundschuh R, Fredrick K. Identification of leader-trailer helices of precursor ribosomal RNA in all phyla of bacteria and archaea. RNA (NEW YORK, N.Y.) 2024; 30:1264-1276. [PMID: 39043438 PMCID: PMC11404451 DOI: 10.1261/rna.080091.124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2024] [Accepted: 07/10/2024] [Indexed: 07/25/2024]
Abstract
Ribosomal RNAs are transcribed as part of larger precursor molecules. In Escherichia coli, complementary RNA segments flank each rRNA and form long leader-trailer (LT) helices, which are crucial for subunit biogenesis in the cell. A previous study of 15 representative species suggested that most but not all prokaryotes contain LT helices. Here, we use a combination of in silico folding and covariation methods to identify and characterize LT helices in 4464 bacterial and 260 archaeal organisms. Our results suggest that LT helices are present in all phyla, including Deinococcota, which had previously been suspected to lack LT helices. In very few organisms, our pipeline failed to detect LT helices for both 16S and 23S rRNA. However, a closer case-by-case look revealed that LT helices are indeed present but escaped initial detection. Over 3600 secondary structure models, many well supported by nucleotide covariation, were generated. These structures show a high degree of diversity. Yet, all exhibit extensive base-pairing between the leader and trailer strands, in line with a common and essential function.
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MESH Headings
- Nucleic Acid Conformation
- RNA, Archaeal/genetics
- RNA, Archaeal/chemistry
- RNA, Archaeal/metabolism
- Archaea/genetics
- RNA, Bacterial/genetics
- RNA, Bacterial/chemistry
- RNA, Bacterial/metabolism
- RNA, Ribosomal/genetics
- RNA, Ribosomal/chemistry
- RNA, Ribosomal/metabolism
- Bacteria/genetics
- RNA Precursors/genetics
- RNA Precursors/metabolism
- RNA Precursors/chemistry
- RNA, Ribosomal, 23S/genetics
- RNA, Ribosomal, 23S/chemistry
- RNA, Ribosomal, 23S/metabolism
- Base Sequence
- RNA, Ribosomal, 16S/genetics
- RNA, Ribosomal, 16S/chemistry
- Base Pairing
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3
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Warner BR, Fredrick K. Contribution of an alternative 16S rRNA helix to biogenesis of the 30S subunit of the ribosome. RNA (NEW YORK, N.Y.) 2024; 30:770-778. [PMID: 38570183 PMCID: PMC11182017 DOI: 10.1261/rna.079960.124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Accepted: 03/23/2024] [Indexed: 04/05/2024]
Abstract
30S subunits become inactive upon exposure to low Mg2+ concentration, because of a reversible conformational change that entails nucleotides (nt) in the neck helix (h28) and 3' tail of 16S rRNA. This active-to-inactive transition involves partial unwinding of h28 and repairing of nt 921-923 with nt 1532-1534, which requires flipping of the 3' tail by ∼180°. Growing evidence suggests that immature 30S particles adopt the inactive conformation in the cell, and transition to the active state occurs at a late stage of maturation. Here, we target nucleotides that form the alternative helix (hALT) of the inactive state. Using an orthogonal ribosome system, we find that disruption of hALT decreases translation activity in the cell modestly, by approximately twofold, without compromising ribosome fidelity. Ribosomes carrying substitutions at positions 1532-1533 support the growth of Escherichia coli strain Δ7 prrn (which carries a single rRNA operon), albeit at rates 10%-20% slower than wild-type ribosomes. These mutant Δ7 prrn strains accumulate free 30S particles and precursor 17S rRNA, indicative of biogenesis defects. Analysis of purified control and mutant subunits suggests that hALT stabilizes the inactive state by 1.2 kcal/mol with little-to-no impact on the active state or the transition state of conversion.
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4
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Naeem FM, Gemler BT, McNutt ZA, Bundschuh R, Fredrick K. Analysis of programmed frameshifting during translation of prfB in Flavobacterium johnsoniae. RNA (NEW YORK, N.Y.) 2024; 30:136-148. [PMID: 37949662 PMCID: PMC10798248 DOI: 10.1261/rna.079721.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Accepted: 10/27/2023] [Indexed: 11/12/2023]
Abstract
Ribosomes of Bacteroidia fail to recognize Shine-Dalgarno (SD) sequences due to sequestration of the 3' tail of the 16S rRNA on the 30S platform. Yet in these organisms, the prfB gene typically contains the programmed +1 frameshift site with its characteristic SD sequence. Here, we investigate prfB autoregulation in Flavobacterium johnsoniae, a member of the Bacteroidia. We find that the efficiency of prfB frameshifting in F. johnsoniae is low (∼7%) relative to that in Escherichia coli (∼50%). Mutation or truncation of bS21 in F. johnsoniae increases frameshifting substantially, suggesting that anti-SD (ASD) sequestration is responsible for the reduced efficiency. The frameshift site of certain Flavobacteriales, such as Winogradskyella psychrotolerans, has no SD. In F. johnsoniae, this W. psychrotolerans sequence supports frameshifting as well as the native sequence, and mutation of bS21 causes no enhancement. These data suggest that prfB frameshifting normally occurs without SD-ASD pairing, at least under optimal laboratory growth conditions. Chromosomal mutations that remove the frameshift or ablate the SD confer subtle growth defects in the presence of paraquat or streptomycin, respectively, indicating that both the autoregulatory mechanism and the SD element contribute to F. johnsoniae cell fitness. Analysis of prfB frameshift sites across 2686 representative bacteria shows loss of the SD sequence in many clades, with no obvious relationship to genome-wide SD usage. These data reveal unexpected variation in the mechanism of frameshifting and identify another group of organisms, the Verrucomicrobiales, that globally lack SD sequences.
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5
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Warner BR, Bundschuh R, Fredrick K. Roles of the leader-trailer helix and antitermination complex in biogenesis of the 30S ribosomal subunit. Nucleic Acids Res 2023; 51:5242-5254. [PMID: 37102690 PMCID: PMC10250234 DOI: 10.1093/nar/gkad316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 04/07/2023] [Accepted: 04/13/2023] [Indexed: 04/28/2023] Open
Abstract
Ribosome biogenesis occurs co-transcriptionally and entails rRNA folding, ribosomal protein binding, rRNA processing, and rRNA modification. In most bacteria, the 16S, 23S and 5S rRNAs are co-transcribed, often with one or more tRNAs. Transcription involves a modified RNA polymerase, called the antitermination complex, which forms in response to cis-acting elements (boxB, boxA and boxC) in the nascent pre-rRNA. Sequences flanking the rRNAs are complementary and form long helices known as leader-trailer helices. Here, we employed an orthogonal translation system to interrogate the functional roles of these RNA elements in 30S subunit biogenesis in Escherichia coli. Mutations that disrupt the leader-trailer helix caused complete loss of translation activity, indicating that this helix is absolutely essential for active subunit formation in the cell. Mutations of boxA also reduced translation activity, but by only 2- to 3-fold, suggesting a smaller role for the antitermination complex. Similarly modest drops in activity were seen upon deletion of either or both of two leader helices, termed here hA and hB. Interestingly, subunits formed in the absence of these leader features exhibited defects in translational fidelity. These data suggest that the antitermination complex and precursor RNA elements help to ensure quality control during ribosome biogenesis.
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6
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McNutt ZA, Roy B, Gemler BT, Shatoff EA, Moon KM, Foster L, Bundschuh R, Fredrick K. Ribosomes lacking bS21 gain function to regulate protein synthesis in Flavobacterium johnsoniae. Nucleic Acids Res 2023; 51:1927-1942. [PMID: 36727479 PMCID: PMC9976891 DOI: 10.1093/nar/gkad047] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 01/12/2023] [Accepted: 01/16/2023] [Indexed: 02/03/2023] Open
Abstract
Ribosomes of Bacteroidia (formerly Bacteroidetes) fail to recognize Shine-Dalgarno (SD) sequences even though they harbor the anti-SD (ASD) of 16S rRNA. Inhibition of SD-ASD pairing is due to sequestration of the 3' tail of 16S rRNA in a pocket formed by bS21, bS18, and bS6 on the 30S platform. Interestingly, in many Flavobacteriales, the gene encoding bS21, rpsU, contains an extended SD sequence. In this work, we present genetic and biochemical evidence that bS21 synthesis in Flavobacterium johnsoniae is autoregulated via a subpopulation of ribosomes that specifically lack bS21. Mutation or depletion of bS21 in the cell increases translation of reporters with strong SD sequences, such as rpsU'-gfp, but has no effect on other reporters. Purified ribosomes lacking bS21 (or its C-terminal region) exhibit higher rates of initiation on rpsU mRNA and lower rates of initiation on other (SD-less) mRNAs than control ribosomes. The mechanism of autoregulation depends on extensive pairing between mRNA and 16S rRNA, and exceptionally strong SD sequences, with predicted pairing free energies of < -13 kcal/mol, are characteristic of rpsU across the Bacteroidota. This work uncovers a clear example of specialized ribosomes in bacteria.
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7
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Zayed AA, Wainaina JM, Dominguez-Huerta G, Pelletier E, Guo J, Mohssen M, Tian F, Pratama AA, Bolduc B, Zablocki O, Cronin D, Solden L, Delage E, Alberti A, Aury JM, Carradec Q, da Silva C, Labadie K, Poulain J, Ruscheweyh HJ, Salazar G, Shatoff E, Coordinators TO, Bundschuh R, Fredrick K, Kubatko LS, Chaffron S, Culley AI, Sunagawa S, Kuhn JH, Wincker P, Sullivan MB. Cryptic and abundant marine viruses at the evolutionary origins of Earth's RNA virome. Science 2022; 376:156-162. [PMID: 35389782 PMCID: PMC10990476 DOI: 10.1126/science.abm5847] [Citation(s) in RCA: 104] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Whereas DNA viruses are known to be abundant, diverse, and commonly key ecosystem players, RNA viruses are insufficiently studied outside disease settings. In this study, we analyzed ≈28 terabases of Global Ocean RNA sequences to expand Earth's RNA virus catalogs and their taxonomy, investigate their evolutionary origins, and assess their marine biogeography from pole to pole. Using new approaches to optimize discovery and classification, we identified RNA viruses that necessitate substantive revisions of taxonomy (doubling phyla and adding >50% new classes) and evolutionary understanding. "Species"-rank abundance determination revealed that viruses of the new phyla "Taraviricota," a missing link in early RNA virus evolution, and "Arctiviricota" are widespread and dominant in the oceans. These efforts provide foundational knowledge critical to integrating RNA viruses into ecological and epidemiological models.
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8
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McNutt ZA, Gandhi MD, Shatoff EA, Roy B, Devaraj A, Bundschuh R, Fredrick K. Comparative Analysis of anti-Shine- Dalgarno Function in Flavobacterium johnsoniae and Escherichia coli. Front Mol Biosci 2021; 8:787388. [PMID: 34966783 PMCID: PMC8710568 DOI: 10.3389/fmolb.2021.787388] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 11/08/2021] [Indexed: 12/03/2022] Open
Abstract
The anti-Shine-Dalgarno (ASD) sequence of 16S rRNA is highly conserved across Bacteria, and yet usage of Shine-Dalgarno (SD) sequences in mRNA varies dramatically, depending on the lineage. Here, we compared the effects of ASD mutagenesis in Escherichia coli, a Gammaproteobacteria which commonly employs SD sequences, and Flavobacterium johnsoniae, a Bacteroidia which rarely does. In E. coli, 30S subunits carrying any single substitution at positions 1,535–1,539 confer dominant negative phenotypes, whereas subunits with mutations at positions 1,540–1,542 are sufficient to support cell growth. These data suggest that CCUCC (1,535–1,539) represents the functional core of the element in E. coli. In F. johnsoniae, deletion of three ribosomal RNA (rrn) operons slowed growth substantially, a phenotype largely rescued by a plasmid-borne copy of the rrn operon. Using this complementation system, we found that subunits with single mutations at positions 1,535–1,537 are as active as control subunits, in sharp contrast to the E. coli results. Moreover, subunits with quadruple substitution or complete replacement of the ASD retain substantial, albeit reduced, activity. Sedimentation analysis revealed that these mutant subunits are overrepresented in the subunit fractions and underrepresented in polysome fractions, suggesting some defect in 30S biogenesis and/or translation initiation. Nonetheless, our collective data indicate that the ASD plays a much smaller role in F. johnsoniae than in E. coli, consistent with SD usage in the two organisms.
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9
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Shatoff EA, Gemler BT, Bundschuh R, Fredrick K. Maturation of 23S rRNA includes removal of helix H1 in many bacteria. RNA Biol 2021; 18:856-865. [PMID: 34812116 PMCID: PMC8782170 DOI: 10.1080/15476286.2021.2000793] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
In most bacteria, the three ribosomal RNAs (rRNAs) are encoded together in each of several near-identical operons. As soon as the nascent precursor rRNA emerges from RNA polymerase, ribosome assembly begins. This process entails ribosomal protein binding, rRNA folding, rRNA modification, and rRNA processing. In the model organisms Escherichia coli and Bacillus subtilis, rRNA processing results in similar mature rRNAs, despite substantial differences in the cohort of RNAses involved. A recent study of Flavobacterium johnsoniae, a member of the phylum Bacteroidota (formerly Bacteroidetes), revealed that helix H1 of 23S rRNA is absent from ribosomes, apparently a consequence of rRNA maturation. In this work, we mined RNA-seq data from 19 individual organisms and ocean metatranscriptomic samples to compare rRNA processing across diverse bacterial lineages. We found that mature ribosomes from multiple clades lack H1, and typically these ribosomes also lack an encoded H98. For all groups analysed, H1 is predicted to form in precursor rRNA as part of a longer leader-trailer helix. Hence, we infer that evolutionary loss of H98 sets the stage for H1 removal during 50S subunit maturation.
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10
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del Peso Santos T, Alvarez L, Sit B, Irazoki O, Blake J, Warner BR, Warr AR, Bala A, Benes V, Waldor MK, Fredrick K, Cava F. BipA exerts temperature-dependent translational control of biofilm-associated colony morphology in Vibrio cholerae. eLife 2021; 10:e60607. [PMID: 33588990 PMCID: PMC7886329 DOI: 10.7554/elife.60607] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 02/03/2021] [Indexed: 12/18/2022] Open
Abstract
Adaptation to shifting temperatures is crucial for the survival of the bacterial pathogen Vibrio cholerae. Here, we show that colony rugosity, a biofilm-associated phenotype, is regulated by temperature in V. cholerae strains that naturally lack the master biofilm transcriptional regulator HapR. Using transposon-insertion mutagenesis, we found the V. cholerae ortholog of BipA, a conserved ribosome-associated GTPase, is critical for this temperature-dependent phenomenon. Proteomic analyses revealed that loss of BipA alters the synthesis of >300 proteins in V. cholerae at 22°C, increasing the production of biofilm-related proteins including the key transcriptional activators VpsR and VpsT, as well as proteins important for diverse cellular processes. At low temperatures, BipA protein levels increase and are required for optimal ribosome assembly in V. cholerae, suggesting that control of BipA abundance is a mechanism by which bacteria can remodel their proteomes. Our study reveals a remarkable new facet of V. cholerae's complex biofilm regulatory network.
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11
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Jha V, Roy B, Jahagirdar D, McNutt ZA, Shatoff EA, Boleratz BL, Watkins DE, Bundschuh R, Basu K, Ortega J, Fredrick K. Structural basis of sequestration of the anti-Shine-Dalgarno sequence in the Bacteroidetes ribosome. Nucleic Acids Res 2021; 49:547-567. [PMID: 33330920 PMCID: PMC7797042 DOI: 10.1093/nar/gkaa1195] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Revised: 11/18/2020] [Accepted: 11/24/2020] [Indexed: 11/25/2022] Open
Abstract
Genomic studies have indicated that certain bacterial lineages such as the Bacteroidetes lack Shine-Dalgarno (SD) sequences, and yet with few exceptions ribosomes of these organisms carry the canonical anti-SD (ASD) sequence. Here, we show that ribosomes purified from Flavobacterium johnsoniae, a representative of the Bacteroidetes, fail to recognize the SD sequence of mRNA in vitro. A cryo-electron microscopy structure of the complete 70S ribosome from F. johnsoniae at 2.8 Å resolution reveals that the ASD is sequestered by ribosomal proteins bS21, bS18 and bS6, explaining the basis of ASD inhibition. The structure also uncovers a novel ribosomal protein—bL38. Remarkably, in F. johnsoniae and many other Flavobacteriia, the gene encoding bS21 contains a strong SD, unlike virtually all other genes. A subset of Flavobacteriia have an alternative ASD, and in these organisms the fully complementary sequence lies upstream of the bS21 gene, indicative of natural covariation. In other Bacteroidetes classes, strong SDs are frequently found upstream of the genes for bS21 and/or bS18. We propose that these SDs are used as regulatory elements, enabling bS21 and bS18 to translationally control their own production.
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12
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Chen M, Fredrick K. RNA Polymerase's Relationship with the Ribosome: Not So Physical, Most of the Time. J Mol Biol 2020; 432:3981-3986. [PMID: 32198117 DOI: 10.1016/j.jmb.2020.03.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 03/03/2020] [Accepted: 03/11/2020] [Indexed: 01/19/2023]
Abstract
In bacteria, the rates of transcription elongation and translation elongation are coordinated, changing together in response to growth conditions. It has been proposed that this is due to physical coupling of RNA polymerase and the lead ribosome on nascent mRNA, an interaction important for preventing premature transcription termination by Rho factor. Recent studies challenge this view and provide evidence that coordination is indirect, mediated in Escherichia coli by the alarmone (p)ppGpp. Here, we discuss these new findings and how they shape our understanding of the functional relationship between RNA polymerase and the ribosome as well as the basis of transcriptional polarity.
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13
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Ying L, Zhu H, Fosso MY, Garneau-Tsodikova S, Fredrick K. Modified Aminoglycosides Bind Nucleic Acids in High-Molecular-Weight Complexes. Antibiotics (Basel) 2020; 9:antibiotics9020093. [PMID: 32098020 PMCID: PMC7168264 DOI: 10.3390/antibiotics9020093] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 02/17/2020] [Accepted: 02/18/2020] [Indexed: 12/05/2022] Open
Abstract
Aminoglycosides represent a large group of antibiotics well known for their ability to target the bacterial ribosome. In studying 6”-substituted variants of the aminoglycoside tobramycin, we serendipitously found that compounds with C12 or C14 linear alkyl substituents potently inhibit reverse transcription in vitro. Initial observations suggested specific inhibition of reverse transcriptase. However, further analysis showed that these and related compounds bind nucleic acids with high affinity, forming high-molecular weight complexes. Stable complex formation is observed with DNA or RNA in single- or double-stranded form. Given the amphiphilic nature of these aminoglycoside derivatives, they likely form micelles and/or vesicles with surface-bound nucleic acids. Hence, these compounds may be useful tools to localize nucleic acids to surfaces or deliver nucleic acids to cells or organelles.
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14
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Baez WD, Roy B, McNutt ZA, Shatoff EA, Chen S, Bundschuh R, Fredrick K. Global analysis of protein synthesis in Flavobacterium johnsoniae reveals the use of Kozak-like sequences in diverse bacteria. Nucleic Acids Res 2019; 47:10477-10488. [PMID: 31602466 PMCID: PMC6847099 DOI: 10.1093/nar/gkz855] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 09/16/2019] [Accepted: 09/30/2019] [Indexed: 12/31/2022] Open
Abstract
In all cells, initiation of translation is tuned by intrinsic features of the mRNA. Here, we analyze translation in Flavobacterium johnsoniae, a representative of the Bacteroidetes. Members of this phylum naturally lack Shine-Dalgarno (SD) sequences in their mRNA, and yet their ribosomes retain the conserved anti-SD sequence. Translation initiation is tuned by mRNA secondary structure and by the identities of several key nucleotides upstream of the start codon. Positive determinants include adenine at position -3, reminiscent of the Kozak sequence of Eukarya. Comparative analysis of Escherichia coli reveals use of the same Kozak-like sequence to enhance initiation, suggesting an ancient and widespread mechanism. Elimination of contacts between A-3 and the conserved β-hairpin of ribosomal protein uS7 fails to diminish the contribution of A-3 to initiation, suggesting an indirect mode of recognition. Also, we find that, in the Bacteroidetes, the trinucleotide AUG is underrepresented in the vicinity of the start codon, which presumably helps compensate for the absence of SD sequences in these organisms.
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15
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Hoffer ED, Maehigashi T, Fredrick K, Dunham CM. Ribosomal ambiguity (ram) mutations promote the open (off) to closed (on) transition and thereby increase miscoding. Nucleic Acids Res 2019; 47:1557-1563. [PMID: 30476222 PMCID: PMC6379664 DOI: 10.1093/nar/gky1178] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Revised: 10/31/2018] [Accepted: 11/05/2018] [Indexed: 01/18/2023] Open
Abstract
Decoding is thought to be governed by a conformational transition in the ribosome—open (off) to closed (on)—that occurs upon codon–anticodon pairing in the A site. Ribosomal ambiguity (ram) mutations increase miscoding and map to disparate regions, consistent with a role for ribosome dynamics in decoding, yet precisely how these mutations act has been unclear. Here, we solved crystal structures of 70S ribosomes harboring 16S ram mutations G299A and G347U in the absence A-site tRNA (A-tRNA) and in the presence of a near-cognate anticodon stem-loop (ASL). In the absence of an A-tRNA, each of the mutant ribosomes exhibits a partially closed (on) state. In the 70S-G347U structure, the 30S shoulder is rotated inward and intersubunit bridge B8 is disrupted. In the 70S-G299A structure, the 30S shoulder is rotated inward and decoding nucleotide G530 flips into the anti conformation. Both of these mutant ribosomes adopt the fully closed (on) conformation in the presence of near-cognate A-tRNA, just as they do with cognate A-tRNA. Thus, these ram mutations act by promoting the open (off) to closed (on) transition, albeit in somewhat distinct ways. This work reveals the functional importance of 30S shoulder rotation for productive aminoacylated-tRNA incorporation.
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16
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Hoffer ED, Maehigashi T, Fredrick K, Dunham CM. Ribosomal ambiguity (
ram
) mutations promote 30S domain closure and thereby increase miscoding. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.628.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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17
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Ying L, Zhu H, Shoji S, Fredrick K. Roles of specific aminoglycoside-ribosome interactions in the inhibition of translation. RNA (NEW YORK, N.Y.) 2019; 25:247-254. [PMID: 30413565 PMCID: PMC6348987 DOI: 10.1261/rna.068460.118] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 11/06/2018] [Indexed: 05/18/2023]
Abstract
Aminoglycosides containing a 2-deoxystreptamine core (AGs) represent a large family of antibiotics that target the ribosome. These compounds promote miscoding, inhibit translocation, and inhibit ribosome recycling. AG binding to helix h44 of the small subunit induces rearrangement of A-site nucleotides A1492 and A1493, which promotes a key open-to-closed conformational change of the subunit and thereby increases miscoding. Mechanisms by which AGs inhibit translocation and recycling remain less clear. Structural studies have revealed a secondary AG binding site in H69 of the large subunit, and it has been proposed that interaction at this site is crucial for inhibition of translocation and recycling. Here, we analyze ribosomes with mutations targeting either or both AG binding sites. Assaying translocation, we find that ablation of the h44 site increases the IC50 values for AGs dramatically, while removal of the H69 site increases these values modestly. This suggests that the AG-h44 interaction is primarily responsible for inhibition, with H69 playing a minor role. Assaying recycling, we find that mutation of h44 has no effect on AG inhibition, consistent with a primary role for AG-H69 interaction. Collectively, these findings help clarify the roles of the two AG binding sites in mechanisms of inhibition by these compounds.
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Zhao D, Baez WD, Fredrick K, Bundschuh R. RiboProP: a probabilistic ribosome positioning algorithm for ribosome profiling. Bioinformatics 2018; 35:1486-1493. [DOI: 10.1093/bioinformatics/bty854] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2018] [Revised: 09/03/2018] [Accepted: 10/09/2018] [Indexed: 11/14/2022] Open
Abstract
Abstract
Motivation
Ribosome profiling has been widely used to study translation in a genome-wide fashion. It requires deep sequencing of ribosome protected mRNA fragments followed by mapping of fragments to the reference genome. For applications such as identification of ribosome pausing sites, it is not enough to map a fragment to a given gene, but the exact position of the ribosome represented by the fragment must be identified for each mRNA fragment. The assignment of the correct ribosome position is complicated by the broad length distribution of the ribosome protected fragments caused by the known sequence bias of micrococcal nuclease (MNase), the most widely used nuclease for digesting mRNAs in bacteria. Available mapping algorithms suffer from either MNase bias or low accuracy in characterizing the ribosome pausing kinetics.
Results
In this paper, we introduce a new computational method for mapping the ribosome protected fragments to ribosome locations. We first develop a mathematical model of the interplay between MNase digestion and ribosome protection of the mRNAs. We then use the model to reconstruct the ribosome occupancy profile on a per gene level. We demonstrate that our method has the capability of mitigating the sequence bias introduced by MNase and accurately locating ribosome pausing sites at codon resolution. We believe that our method can be broadly applied to ribosome profiling studies on bacteria where codon resolution is necessary.
Availability and implementation
Source code implementing our approach can be downloaded under GPL3 license at http://bioserv.mps.ohio-state.edu/RiboProP.
Supplementary information
Supplementary data are available at Bioinformatics online.
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Vo MN, Terrey M, Lee JW, Roy B, Moresco JJ, Sun L, Fu H, Liu Q, Weber TG, Yates JR, Fredrick K, Schimmel P, Ackerman SL. Publisher Correction: ANKRD16 prevents neuron loss caused by an editing-defective tRNA synthetase. Nature 2018; 560:E35. [PMID: 29925958 DOI: 10.1038/s41586-018-0271-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In the Fig. 3b western blot of this Article, 'Myc-AlaRS' in row one should have been 'Myc-AAD Aars', 'AlaRS' in row two should have been 'Aars' and 'ANKRD16' in row four should have been 'Ankrd16'. In Fig. 4f, 'ANKRD16' and 'ANKRD16(3xR)' should have been 'Ankrd16' and 'Ankrd163xR; and in Fig. 3c the position of the molecular mass markers had shifted. These figures have been corrected online, and see Supplementary Information to the accompanying Amendment for the original figure.
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Vo MN, Terrey M, Lee JW, Roy B, Moresco JJ, Sun L, Fu H, Liu Q, Weber TG, Yates JR, Fredrick K, Schimmel P, Ackerman SL. ANKRD16 prevents neuron loss caused by an editing-defective tRNA synthetase. Nature 2018; 557:510-515. [PMID: 29769718 PMCID: PMC5973781 DOI: 10.1038/s41586-018-0137-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2017] [Accepted: 04/09/2018] [Indexed: 11/29/2022]
Abstract
Editing domains of aminoacyl tRNA synthetases correct tRNA charging errors to maintain translational fidelity. A mutation in the editing domain of alanyl tRNA synthetase (AlaRS) in Aars sti mutant mice results in an increase in the production of serine-mischarged tRNAAla and the degeneration of cerebellar Purkinje cells. Here, using positional cloning, we identified Ankrd16, a gene that acts epistatically with the Aars sti mutation to attenuate neurodegeneration. ANKRD16, a vertebrate-specific protein that contains ankyrin repeats, binds directly to the catalytic domain of AlaRS. Serine that is misactivated by AlaRS is captured by the lysine side chains of ANKRD16, which prevents the charging of serine adenylates to tRNAAla and precludes serine misincorporation in nascent peptides. The deletion of Ankrd16 in the brains of Aarssti/sti mice causes widespread protein aggregation and neuron loss. These results identify an amino-acid-accepting co-regulator of tRNA synthetase editing as a new layer of the machinery that is essential to the prevention of severe pathologies that arise from defects in editing.
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Gibbs MR, Fredrick K. Roles of elusive translational GTPases come to light and inform on the process of ribosome biogenesis in bacteria. Mol Microbiol 2017; 107:445-454. [PMID: 29235176 DOI: 10.1111/mmi.13895] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 12/07/2017] [Accepted: 12/08/2017] [Indexed: 12/25/2022]
Abstract
Protein synthesis relies on several translational GTPases (trGTPases), related proteins that couple the hydrolysis of GTP to specific molecular events on the ribosome. Most bacterial trGTPases, including IF2, EF-Tu, EF-G and RF3, play well-known roles in translation. The cellular functions of LepA (also termed EF4) and BipA (also termed TypA), conversely, have remained enigmatic. Recent studies provide compelling in vivo evidence that LepA and BipA function in biogenesis of the 30S and 50S subunit respectively. These findings have important implications for ribosome biogenesis in bacteria. Because the GTPase activity of each of these proteins depends on interactions with both ribosomal subunits, some portion of 30S and 50S assembly must occur in the context of the 70S ribosome. In this review, we introduce the trGTPases of bacteria, describe the new functional data on LepA and BipA, and discuss the how these findings shape our current view of ribosome biogenesis in bacteria.
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Roy B, Liu Q, Shoji S, Fredrick K. IF2 and unique features of initiator tRNA fMet help establish the translational reading frame. RNA Biol 2017; 15:604-613. [PMID: 28914580 DOI: 10.1080/15476286.2017.1379636] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Translation begins at AUG, GUG, or UUG codons in bacteria. Start codon recognition occurs in the P site, which may help explain this first-position degeneracy. However, the molecular basis of start codon specificity remains unclear. In this study, we measured the codon dependence of 30S•mRNA•tRNAfMet and 30S•mRNA•tRNAMet complex formation. We found that complex stability varies over a large range with initiator tRNAfMet, following the same trend as reported previously for initiation rate in vivo (AUG > GUG, UUG > CUG, AUC, AUA > ACG). With elongator tRNAMet, the codon dependence of binding differs qualitatively, with virtually no discrimination between GUG and CUG. A unique feature of initiator tRNAfMet is a series of three G-C basepairs in the anticodon stem, which are known to be important for efficient initiation in vivo. A mutation targeting the central of these G-C basepairs causes the mRNA binding specificity pattern to change in a way reminiscent of elongator tRNAMet. Unexpectedly, for certain complexes containing fMet-tRNAfMet, we observed mispositioning of mRNA, such that codon 2 is no longer programmed in the A site. This mRNA mispositioning is exacerbated by the anticodon stem mutation and suppressed by IF2. These findings suggest that both IF2 and the unique anticodon stem of fMet-tRNAfMet help constrain mRNA positioning to set the correct reading frame during initiation.
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Dai X, Zhu M, Warren M, Balakrishnan R, Patsalo V, Okano H, Williamson JR, Fredrick K, Wang YP, Hwa T. Reduction of translating ribosomes enables Escherichia coli to maintain elongation rates during slow growth. Nat Microbiol 2016; 2:16231. [PMID: 27941827 PMCID: PMC5346290 DOI: 10.1038/nmicrobiol.2016.231] [Citation(s) in RCA: 185] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2016] [Accepted: 10/17/2016] [Indexed: 01/13/2023]
Abstract
Bacteria growing under different conditions experience a broad range of demand on the rate of protein synthesis, which profoundly affects cellular resource allocation. During fast growth, protein synthesis has long been known to be modulated by adjusting the ribosome content, with the vast majority of ribosomes engaged at a near-maximal rate of elongation. Here, we systematically characterize protein synthesis by Escherichia coli, focusing on slow-growth conditions. We establish that the translational elongation rate decreases as growth slows, exhibiting a Michaelis-Menten dependence on the abundance of the cellular translational apparatus. However, an appreciable elongation rate is maintained even towards zero growth, including the stationary phase. This maintenance, critical for timely protein synthesis in harsh environments, is accompanied by a drastic reduction in the fraction of active ribosomes. Interestingly, well-known antibiotics such as chloramphenicol also cause a substantial reduction in the pool of active ribosomes, instead of slowing down translational elongation as commonly thought.
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Ying L, Fredrick K. Epistasis analysis of 16S rRNA ram mutations helps define the conformational dynamics of the ribosome that influence decoding. RNA (NEW YORK, N.Y.) 2016; 22:499-505. [PMID: 26873598 PMCID: PMC4793206 DOI: 10.1261/rna.054486.115] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 01/14/2016] [Indexed: 06/05/2023]
Abstract
The ribosome actively participates in decoding, with a tRNA-dependent rearrangement of the 30S A site playing a key role. Ribosomal ambiguity (ram) mutations have mapped not only to the A site but also to the h12/S4/S5 region and intersubunit bridge B8, implicating other conformational changes such as 30S shoulder rotation and B8 disruption in the mechanism of decoding. Recent crystallographic data have revealed that mutation G299A in helix h12 allosterically promotes B8 disruption, raising the question of whether G299A and/or other ram mutations act mainly via B8. Here, we compared the effects of each of several ram mutations in the absence and presence of mutation h8Δ2, which effectively takes out bridge B8. The data obtained suggest that a subset of mutations including G299A act in part via B8 but predominantly through another mechanism. We also found that G299A in h12 and G347U in h14 each stabilize tRNA in the A site. Collectively, these data support a model in which rearrangement of the 30S A site, inward shoulder rotation, and bridge B8 disruption are loosely coupled events, all of which promote progression along the productive pathway toward peptide bond formation.
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Liu Q, Fredrick K. Intersubunit Bridges of the Bacterial Ribosome. J Mol Biol 2016; 428:2146-64. [PMID: 26880335 DOI: 10.1016/j.jmb.2016.02.009] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 01/29/2016] [Accepted: 02/05/2016] [Indexed: 02/02/2023]
Abstract
The ribosome is a large two-subunit ribonucleoprotein machine that translates the genetic code in all cells, synthesizing proteins according to the sequence of the mRNA template. During translation, the primary substrates, transfer RNAs, pass through binding sites formed between the two subunits. Multiple interactions between the ribosomal subunits, termed intersubunit bridges, keep the ribosome intact and at the same time govern dynamics that facilitate the various steps of translation such as transfer RNA-mRNA movement. Here, we review the molecular nature of these intersubunit bridges, how they change conformation during translation, and their functional roles in the process.
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