1
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Lahry K, Datta M, Varshney U. Genetic analysis of translation initiation in bacteria: An initiator tRNA-centric view. Mol Microbiol 2024. [PMID: 38410838 DOI: 10.1111/mmi.15243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 02/03/2024] [Accepted: 02/09/2024] [Indexed: 02/28/2024]
Abstract
Translation of messenger RNA (mRNA) in bacteria occurs in the steps of initiation, elongation, termination, and ribosome recycling. The initiation step comprises multiple stages and uses a special transfer RNA (tRNA) called initiator tRNA (i-tRNA), which is first aminoacylated and then formylated using methionine and N10 -formyl-tetrahydrofolate (N10 -fTHF), respectively. Both methionine and N10 -fTHF are produced via one-carbon metabolism, linking translation initiation with active cellular metabolism. The fidelity of i-tRNA binding to the ribosomal peptidyl-site (P-site) is attributed to the structural features in its acceptor stem, and the highly conserved three consecutive G-C base pairs (3GC pairs) in the anticodon stem. The acceptor stem region is important in formylation of the amino acid attached to i-tRNA and in its initial binding to the P-site. And, the 3GC pairs are crucial in transiting the i-tRNA through various stages of initiation. We utilized the feature of 3GC pairs to investigate the nuanced layers of scrutiny that ensure fidelity of translation initiation through i-tRNA abundance and its interactions with the components of the translation apparatus. We discuss the importance of i-tRNA in the final stages of ribosome maturation, as also the roles of the Shine-Dalgarno sequence, ribosome heterogeneity, initiation factors, ribosome recycling factor, and coevolution of the translation apparatus in orchestrating a delicate balance between the fidelity of initiation and/or its leakiness to generate proteome plasticity in cells to confer growth fitness advantages in response to the dynamic nutritional states.
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Affiliation(s)
- Kuldeep Lahry
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bengaluru, India
| | - Madhurima Datta
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bengaluru, India
| | - Umesh Varshney
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bengaluru, India
- Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, India
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2
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McNutt ZA, Roy B, Gemler BT, Shatoff EA, Moon KM, Foster LJ, 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: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [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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Affiliation(s)
- Zakkary A McNutt
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA.,Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA
| | - Bappaditya Roy
- Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA.,Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - Bryan T Gemler
- Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA.,Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA
| | - Elan A Shatoff
- Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA.,Department of Physics, The Ohio State University, Columbus, OH 43210, USA
| | - Kyung-Mee Moon
- Department of Biochemistry and Molecular Biology, Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, V3T1Z4, Canada
| | - Leonard J Foster
- Department of Biochemistry and Molecular Biology, Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, V3T1Z4, Canada
| | - Ralf Bundschuh
- Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA.,Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210, USA.,Department of Physics, The Ohio State University, Columbus, OH 43210, USA.,Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH 43210, USA.,Division of Hematology, Department of Internal Medicine, The Ohio State University, Columbus, OH 43210, USA
| | - Kurt Fredrick
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA.,Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA.,Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
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3
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Biedenbänder T, de Jesus V, Schmidt-Dengler M, Helm M, Corzilius B, Fürtig B. RNA modifications stabilize the tertiary structure of tRNAfMet by locally increasing conformational dynamics. Nucleic Acids Res 2022; 50:2334-2349. [PMID: 35137185 PMCID: PMC8887418 DOI: 10.1093/nar/gkac040] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 12/29/2021] [Accepted: 01/14/2022] [Indexed: 11/12/2022] Open
Abstract
A plethora of modified nucleotides extends the chemical and conformational space for natural occurring RNAs. tRNAs constitute the class of RNAs with the highest modification rate. The extensive modification modulates their overall stability, the fidelity and efficiency of translation. However, the impact of nucleotide modifications on the local structural dynamics is not well characterized. Here we show that the incorporation of the modified nucleotides in tRNAfMet from Escherichia coli leads to an increase in the local conformational dynamics, ultimately resulting in the stabilization of the overall tertiary structure. Through analysis of the local dynamics by NMR spectroscopic methods we find that, although the overall thermal stability of the tRNA is higher for the modified molecule, the conformational fluctuations on the local level are increased in comparison to an unmodified tRNA. In consequence, the melting of individual base pairs in the unmodified tRNA is determined by high entropic penalties compared to the modified. Further, we find that the modifications lead to a stabilization of long-range interactions harmonizing the stability of the tRNA's secondary and tertiary structure. Our results demonstrate that the increase in chemical space through introduction of modifications enables the population of otherwise inaccessible conformational substates.
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Affiliation(s)
- Thomas Biedenbänder
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität, Frankfurt am Main 60438, Germany.,Institute of Chemistry and Department Life, Light & Matter, University of Rostock, Rostock 18059, Germany
| | - Vanessa de Jesus
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität, Frankfurt am Main 60438, Germany
| | - Martina Schmidt-Dengler
- Institut für pharmazeutische und biomedizinische Wissenschaften (IPBW), Johannes Gutenberg-Universität, Mainz 55128, Germany
| | - Mark Helm
- Institut für pharmazeutische und biomedizinische Wissenschaften (IPBW), Johannes Gutenberg-Universität, Mainz 55128, Germany
| | - Björn Corzilius
- Institute of Chemistry and Department Life, Light & Matter, University of Rostock, Rostock 18059, Germany
| | - Boris Fürtig
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität, Frankfurt am Main 60438, Germany
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4
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Brandi A, Giangrossi M, Paoloni S, Spurio R, Giuliodori AM, Pon CL, Gualerzi CO. Transcriptional and post-transcriptional events trigger de novo infB expression in cold stressed Escherichia coli. Nucleic Acids Res 2019; 47:4638-4651. [PMID: 30916329 PMCID: PMC6511841 DOI: 10.1093/nar/gkz187] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 03/07/2019] [Accepted: 03/22/2019] [Indexed: 11/13/2022] Open
Abstract
After a 37 to 10°C temperature downshift the level of translation initiation factor IF2, like that of IF1 and IF3, increases at least 3-fold with respect to the ribosomes. To clarify the mechanisms and conditions leading to cold-stress induction of infB expression, the consequences of this temperature shift on infB (IF2) transcription, infB mRNA stability and translation were analysed. The Escherichia coli gene encoding IF2 is part of the metY-nusA-infB operon that contains three known promoters (P-1, P0 and P2) in addition to two promoters P3 and P4 identified in this study, the latter committed to the synthesis of a monocistronic mRNA encoding exclusively IF2. The results obtained indicate that the increased level of IF2 following cold stress depends on three mechanisms: (i) activation of all the promoters of the operon, P-1 being the most cold-responsive, as a likely consequence of the reduction of the ppGpp level that follows cold stress; (ii) a large increase in infB mRNA half-life and (iii) the cold-shock induced translational bias that ensures efficient translation of infB mRNA by the translational apparatus of cold shocked cells. A comparison of the mechanisms responsible for the cold shock induction of the three initiation factors is also presented.
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Affiliation(s)
- Anna Brandi
- Laboratory of Genetics, Department of Biosciences and Biotechnology University of Camerino, 62032 Camerino (MC), Italy
| | - Mara Giangrossi
- Laboratory of Genetics, Department of Biosciences and Biotechnology University of Camerino, 62032 Camerino (MC), Italy
| | - Silvia Paoloni
- Laboratory of Genetics, Department of Biosciences and Biotechnology University of Camerino, 62032 Camerino (MC), Italy
| | - Roberto Spurio
- Laboratory of Genetics, Department of Biosciences and Biotechnology University of Camerino, 62032 Camerino (MC), Italy
| | - Anna M Giuliodori
- Laboratory of Genetics, Department of Biosciences and Biotechnology University of Camerino, 62032 Camerino (MC), Italy
| | - Cynthia L Pon
- Laboratory of Genetics, Department of Biosciences and Biotechnology University of Camerino, 62032 Camerino (MC), Italy
| | - Claudio O Gualerzi
- Laboratory of Genetics, Department of Biosciences and Biotechnology University of Camerino, 62032 Camerino (MC), Italy
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5
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Shetty S, Shah RA, Chembazhi UV, Sah S, Varshney U. Two highly conserved features of bacterial initiator tRNAs license them to pass through distinct checkpoints in translation initiation. Nucleic Acids Res 2018; 45:2040-2050. [PMID: 28204695 PMCID: PMC5389676 DOI: 10.1093/nar/gkw854] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 09/14/2016] [Accepted: 09/16/2016] [Indexed: 11/13/2022] Open
Abstract
Eubacterial translation initiation involves assembly of tRNAfMet, mRNA, initiation factors (IFs) and 30S ribosome in a 30S pre-initiation complex (30S pre-IC), which rearranges and joins 50S ribosome to form 70S IC. Upon releasing IFs, 70S IC becomes elongation-competent 70S. The direct recruitment of initiator tRNA (tRNAfMet) into the ribosomal P-site, crucial in accurate initiation of translation, is attributed to two conserved features of tRNAfMet: (i) formylation of amino acid attached to it and, (ii) the presence of three consecutive G-C base pairs (3GC base pairs) in the anticodon stem. However, the precise roles of these two conserved features of tRNAfMet during the various steps of initiation remain unclear. Using natural and engineered tRNAs, we show that the 3GC pairs license tRNAfMet transitions from 30S to 70S IC and then to elongation-competent 70S by release of IF3. Of the 3GC pairs, the middle GC pair (G30-C40), or merely G30 (in a specific context) suffices in this role and is essential for the sustenance of Escherichia coli. Furthermore, rescue of formylase deficient E. coli by overproduced tRNAfMet reveals that the feature of formylation licenses initial targeting of tRNAfMet to 30S ribosome
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Affiliation(s)
- Sunil Shetty
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Riyaz A Shah
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Ullas V Chembazhi
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Shivjee Sah
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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6
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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: 5] [Impact Index Per Article: 0.7] [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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Affiliation(s)
- Bappaditya Roy
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
| | - Qi Liu
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
| | - Shinichiro Shoji
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
| | - Kurt Fredrick
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
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7
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Shetty S, Bhattacharyya S, Varshney U. Is the cellular initiation of translation an exclusive property of the initiator tRNAs? RNA Biol 2016; 12:675-80. [PMID: 25996503 DOI: 10.1080/15476286.2015.1043507] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Translation of mRNAs is the primary function of the ribosomal machinery. Although cells allow for a certain level of translational errors/mistranslation (which may well be a strategic need), maintenance of the fidelity of translation is vital for the cellular function and fitness. The P-site bound initiator tRNA selects the start codon in an mRNA and specifies the reading frame. A direct P-site binding of the initiator tRNA is a function of its special structural features, ribosomal elements, and the initiation factors. A highly conserved feature of the 3 consecutive G:C base pairs (3 GC pairs) in the anticodon stem of the initiator tRNAs is vital in directing it to the P-site. Mutations in the 3 GC pairs diminish/abolish initiation under normal physiological conditions. Using molecular genetics approaches, we have identified conditions that allow initiation with the mutant tRNAs in Escherichia coli. During our studies, we have uncovered a novel phenomenon of in vivo initiation by elongator tRNAs. Here, we recapitulate how the cellular abundance of the initiator tRNA, and nucleoside modifications in rRNA are connected with the tRNA selection in the P-site. We then discuss our recent finding of how a conserved feature in the mRNA, the Shine-Dalgarno sequence, influences tRNA selection in the P-site.
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Affiliation(s)
- Sunil Shetty
- a Department of Microbiology and Cell Biology; Indian Institute of Science ; Bangalore , India
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8
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Sinha A, Köhrer C, Weber MHW, Masuda I, Mootha VK, Hou YM, RajBhandary UL. Biochemical characterization of pathogenic mutations in human mitochondrial methionyl-tRNA formyltransferase. J Biol Chem 2014; 289:32729-41. [PMID: 25288793 DOI: 10.1074/jbc.m114.610626] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
N-Formylation of initiator methionyl-tRNA (Met-tRNA(Met)) by methionyl-tRNA formyltransferase (MTF) is important for translation initiation in bacteria, mitochondria, and chloroplasts. Unlike all other translation systems, the metazoan mitochondrial system is unique in using a single methionine tRNA (tRNA(Met)) for both initiation and elongation. A portion of Met-tRNA(Met) is formylated for initiation, whereas the remainder is used for elongation. Recently, we showed that compound heterozygous mutations within the nuclear gene encoding human mitochondrial MTF (mt-MTF) significantly reduced mitochondrial translation efficiency, leading to combined oxidative phosphorylation deficiency and Leigh syndrome in two unrelated patients. Patient P1 has a stop codon mutation in one of the MTF genes and an S209L mutation in the other MTF gene. P2 has a S125L mutation in one of the MTF genes and the same S209L mutation as P1 in the other MTF gene. Here, we have investigated the effect of mutations at Ser-125 and Ser-209 on activities of human mt-MTF and of the corresponding mutations, Ala-89 or Ala-172, respectively, on activities of Escherichia coli MTF. The S125L mutant has 653-fold lower activity, whereas the S209L mutant has 36-fold lower activity. Thus, both patients depend upon residual activity of the S209L mutant to support low levels of mitochondrial protein synthesis. We discuss the implications of these and other results for whether the effect of the S209L mutation on mitochondrial translational efficiency is due to reduced activity of the mutant mt-MTF and/or reduced levels of the mutant mt-MTF.
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Affiliation(s)
- Akesh Sinha
- From the Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Caroline Köhrer
- From the Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Michael H W Weber
- From the Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Isao Masuda
- the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, and
| | - Vamsi K Mootha
- the Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Ya-Ming Hou
- the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, and
| | - Uttam L RajBhandary
- From the Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139,
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9
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Abstract
Multiple copies of a gene require enhanced investment on the part of the cell and, as such, call for an explanation. The observation that Escherichia coli has four copies of initiator tRNA (tRNAi) genes, encoding a special tRNA (tRNA(fMet)) required to start protein synthesis, is puzzling particularly because the cell appears to be unaffected by the removal of one copy. However, the fitness of an organism has both absolute and relative connotations. Thus, we carried out growth competition experiments between E. coli strains that differ in the number of tRNAi genes they contain. This has enabled us to uncover an unexpected link between the number of tRNAi genes and protein synthesis, nutritional status, and fitness. Wild-type strains with the canonical four tRNAi genes are favored in nutrient-rich environments, and those carrying fewer are favored in nutrient-poor environments. Auxotrophs behave as if they have a nutritionally poor internal environment. A heuristic model that links tRNAi gene copy number, genetic stress, and growth rate accounts for the findings. Our observations provide strong evidence that natural selection can work through seemingly minor quantitative variations in gene copy number and thereby impact organismal fitness.
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10
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Abstract
Of all tRNAs, initiator tRNA is unique in its ability to start protein synthesis by directly binding the ribosomal P-site. This ability is believed to derive from the almost universal presence of three consecutive G-C base (3G-C) pairs in the anticodon stem of initiator tRNA. Consistent with the hypothesis, a plasmid-borne initiator tRNA with one, two, or all 3G-C pairs mutated displays negligible initiation activity when tested in a WT Escherichia coli cell. Given this, the occurrence of unconventional initiator tRNAs lacking the 3G-C pairs, as in some species of Mycoplasma and Rhizobium, is puzzling. We resolve the puzzle by showing that the poor activity of unconventional initiator tRNAs in E. coli is because of competition from a large pool of the endogenous WT initiator tRNA (possessing the 3G-C pairs). We show that E. coli can be sustained on an initiator tRNA lacking the first and third G-C pairs; thereby reducing the 3G-C rule to a mere middle G-C requirement. Two general inferences following from our findings, that the activity of a mutant gene product may depend on its abundance in the cell relative to that of the WT, and that promiscuous initiation with elongator tRNAs has the potential to enhance phenotypic diversity without affecting genomic integrity, have been discussed.
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11
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Abstract
Selection of correct start codons on messenger RNAs is a key step required for faithful translation of the genetic message. Such a selection occurs in a complex process, during which a translation-competent ribosome assembles, eventually having in its P site a specialized methionyl-tRNAMet base-paired with the start codon on the mRNA. This chapter summarizes recent advances describing at the molecular level the successive steps involved in the process. Special emphasis is put on the roles of the three initiation factors and of the initiator tRNA, which are crucial for the efficiency and the specificity of the process. In particular, structural analyses concerning complexes containing ribosomal subunits, as well as detailed kinetic studies, have shed new light on the sequence of events leading to faithful initiation of protein synthesis in Bacteria.
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12
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Transfer RNA-mediated regulation of ribosome dynamics during protein synthesis. Nat Struct Mol Biol 2011; 18:1043-51. [PMID: 21857664 PMCID: PMC3167956 DOI: 10.1038/nsmb.2098] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2010] [Accepted: 06/14/2011] [Indexed: 01/27/2023]
Abstract
Translocation of transfer RNAs (tRNAs) through the ribosome during protein synthesis involves large-scale structural rearrangements of the ribosome and the ribosome-bound tRNAs that are accompanied by extensive and dynamic remodeling of tRNA-ribosome interactions. The contributions that rearranging individual tRNA-ribosome interactions make to directing tRNA movements during translocation, however, remain largely unknown. To address this question, we have used single-molecule fluorescence resonance energy transfer to characterize the dynamics of ribosomal pre-translocation (PRE) complex analogs carrying either wild-type or systematically mutagenized tRNAs. Our data reveal how specific tRNA-ribosome interactions regulate the rate with which the PRE complex rearranges into a critical, on-pathway translocation intermediate and how these interactions control the stability of the resulting configuration. More interestingly, our results suggest that the conformational flexibility of the tRNA molecule itself plays a crucial role in directing the structural dynamics of the PRE complex during translocation.
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13
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Kapoor S, Das G, Varshney U. Crucial contribution of the multiple copies of the initiator tRNA genes in the fidelity of tRNA(fMet) selection on the ribosomal P-site in Escherichia coli. Nucleic Acids Res 2010; 39:202-12. [PMID: 20798174 PMCID: PMC3017606 DOI: 10.1093/nar/gkq760] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The accuracy of the initiator tRNA (tRNAfMet) selection in the ribosomal P-site is central to the fidelity of protein synthesis. A highly conserved occurrence of three consecutive G–C base pairs in the anticodon stem of tRNAfMet contributes to its preferential selection in the P-site. In a genetic screen, using a plasmid borne copy of an inactive tRNAfMet mutant wherein the three G–C base pairs were changed, we isolated Escherichia coli strains that allow efficient initiation with the tRNAfMet mutant. Here, extensive characterization of two such strains revealed novel mutations in the metZWV promoter severely compromising tRNAfMet levels. Low cellular abundance of the chromosomally encoded tRNAfMet allows efficient initiation with the tRNAfMet mutant and an elongator tRNAGln, revealing that a high abundance of the cellular tRNAfMet is crucial for the fidelity of initiator tRNA selection on the ribosomal P-site in E. coli. We discuss possible implications of the changes in the cellular tRNAfMet abundance in proteome remodeling.
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Affiliation(s)
- Suman Kapoor
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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14
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Gaur R, Varshney U. Genetic analysis identifies a function for the queC (ybaX) gene product at an initial step in the queuosine biosynthetic pathway in Escherichia coli. J Bacteriol 2005; 187:6893-901. [PMID: 16199558 PMCID: PMC1251624 DOI: 10.1128/jb.187.20.6893-6901.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Queuosine (Q), one of the most complex modifications occurring at the wobble position of tRNAs with GUN anticodons, is implicated in a number of biological activities, including accuracy of decoding, virulence, and cellular differentiation. Despite these important implications, its biosynthetic pathway has remained unresolved. Earlier, we observed that a naturally occurring strain of Escherichia coli B105 lacked Q modification in the tRNAs. In the present study, we developed a genetic screen to map the defect in E. coli B105 to a single gene, queC (renamed from ybaX), predicted to code for a 231-amino-acid-long protein with a pI of 5.6. As analyzed by mobility of tRNA(Tyr) on acid urea gels and two-dimensional thin-layer chromatography of the modified nucleosides, expression of QueC from a plasmid-borne copy confers a Q+ phenotype to E. coli B105. Further, analyses of tRNA(Tyr) from E. coli JE10651 (queA mutant), its derivative generated by deletion of chromosomal queC (queA deltaqueC), and E. coli JE7325, deficient in converting preQ0 to preQ1, have provided the first genetic evidence for the involvement of QueC at a step leading to production of preQ0, the first known intermediate in the generally accepted pathway that utilizes GTP as the starting molecule. In addition, we discuss the possibilities of collaboration of QueC with other cellular proteins in the production of preQ0.
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Affiliation(s)
- Rahul Gaur
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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15
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Das G, Dineshkumar TK, Thanedar S, Varshney U. Acquisition of a stable mutation in metY allows efficient initiation from an amber codon in Escherichia coli. Microbiology (Reading) 2005; 151:1741-1750. [PMID: 15941983 DOI: 10.1099/mic.0.27915-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Escherichia colistrains harbouring elongator tRNAs that insert amino acids in response to a termination codon during elongation have been generated for various applications. Additionally, it was shown that expression of an initiator tRNA containing a CUA anticodon from a multicopy plasmid inE. coliresulted in initiation from an amber codon. Even though the initiation-based system remedies toxicity-related drawbacks, its usefulness has remained limited for want of a strain with a chromosomally encoded initiator tRNA ‘suppressor’.E. coliK strains possess four initiator tRNA genes: themetZ,metWandmetVgenes, located at a single locus, encode tRNA1fMet, and a distantly locatedmetYgene encodes a variant, tRNA2fMet. In this study, a stable strain ofE. coliK-12 that affords efficient initiation from an amber initiation codon was isolated. Genetic analysis revealed that themetYgene in this strain acquired mutations to encode tRNA2fMetwith a CUA anticodon (a U35A36 mutation). The acquisition of the mutations depended on the presence of a plasmid-borne copy of the mutantmetYandrecA+host background. The mutations were observed when the plasmid-borne gene encoded tRNA2fMet(U35A36) with additional changes in the acceptor stem (G72; G72G73) but not in the anticodon stem (U29C30A31/U35A36/ψ39G40A41). The usefulness of this strain, and a possible role for multiple tRNA1fMetgenes inE. coliin safeguarding their intactness, are discussed.
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Affiliation(s)
- Gautam Das
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - T K Dineshkumar
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Swapna Thanedar
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Umesh Varshney
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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16
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Mayer C, Stortchevoi A, Köhrer C, Varshney U, RajBhandary UL. Initiator tRNA and its role in initiation of protein synthesis. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2003; 66:195-206. [PMID: 12762022 DOI: 10.1101/sqb.2001.66.195] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- C Mayer
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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17
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Dineshkumar TK, Thanedar S, Subbulakshmi C, Varshney U. An unexpected absence of queuosine modification in the tRNAs of an Escherichia coli B strain. MICROBIOLOGY (READING, ENGLAND) 2002; 148:3779-3787. [PMID: 12480882 DOI: 10.1099/00221287-148-12-3779] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The post-transcriptional processing of tRNAs decorates them with a number of modified bases important for their biological functions. Queuosine, found in the tRNAs with GUN anticodons (Asp, Asn, His, Tyr), is an extensively modified base whose biosynthetic pathway is still unclear. In this study, it was observed that the tRNA(Tyr) from Escherichia coli B105 (a B strain) migrated faster than that from E. coli CA274 (a K-12 strain) on acid urea gels. The organization of tRNA(Tyr) genes in E. coli B105 was found to be typical of the B strains. Subsequent analysis of tRNA(Tyr) and tRNA(His) from several strains of E. coli on acid urea gels, and modified base analysis of tRNA preparations enriched for tRNA(Tyr), showed that E. coli B105 lacked queuosine in its tRNAs. However, the lack of queuosine in tRNAs was not a common feature of all E. coli B strains. The tgt and queA genes in B105 were shown to be functional by their ability to complement tgt and queA mutant strains. These observations suggested a block at the step of the biosynthesis of preQ(1) (or preQ(0)) in the B105 strain. Interestingly, a multicopy vector harbouring a functional tgt gene was toxic to E. coli B105 but not to CA274. Also, in mixed cultures, E. coli B105 was readily competed out by the CA274 strain. The importance of these observations and this novel strain (E. coli B105) in unravelling the mechanism of preQ(1) or preQ(0) biosynthesis is discussed.
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MESH Headings
- Electrophoresis, Polyacrylamide Gel
- Escherichia coli/genetics
- Escherichia coli/growth & development
- Escherichia coli/metabolism
- Nucleoside Q/metabolism
- Pentosyltransferases/metabolism
- Pyrimidinones/metabolism
- Pyrroles/metabolism
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Transfer, Tyr/chemistry
- RNA, Transfer, Tyr/genetics
- RNA, Transfer, Tyr/metabolism
- Urea
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Affiliation(s)
- T K Dineshkumar
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1
| | - Swapna Thanedar
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1
| | - C Subbulakshmi
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1
| | - Umesh Varshney
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India1
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18
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Mayer C, RajBhandary UL. Conformational change of Escherichia coli initiator methionyl-tRNA(fMet) upon binding to methionyl-tRNA formyl transferase. Nucleic Acids Res 2002; 30:2844-50. [PMID: 12087168 PMCID: PMC117066 DOI: 10.1093/nar/gkf411] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The specific formylation of initiator methionyl-tRNA (Met-tRNA) by methionyl-tRNA formyltransferase (MTF) is important for the initiation of protein synthesis in Escherichia coli. The determinants for formylation are located in the acceptor stem and in the dihydrouridine (D) stem of the initiator tRNA (tRNA(fMet)). Here, we have used ethylation interference analysis to study the interactions between the Met-tRNA(fMet) and MTF in solution. We have identified three clusters of phosphates in the tRNA that, when ethylated, interfere with binding of MTF. Interference due to ethylation of phosphates in the acceptor stem and in the D stem is most likely due to the close proximity of the protein as seen in the crystal structure of the MTF.fMet-tRNA(fMet) complex. The third cluster of phosphates, whose ethylation interferes with binding of MTF, is dispersed along the anticodon stem, which is distal to the sites of tRNA protein contacts. Interestingly, these latter positions correspond to sites of increased cleavages by RNase V1 in RNA footprinting experiments. Together, these results suggest that in addition to the protein, which binds to the substrate tRNA in an induced fit mechanism, the tRNA also undergoes induced structural changes during its binding to MTF.
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Affiliation(s)
- Christine Mayer
- Department of Biology, 68-671A, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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19
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Köhrer C, Xie L, Kellerer S, Varshney U, RajBhandary UL. Import of amber and ochre suppressor tRNAs into mammalian cells: a general approach to site-specific insertion of amino acid analogues into proteins. Proc Natl Acad Sci U S A 2001; 98:14310-5. [PMID: 11717406 PMCID: PMC64678 DOI: 10.1073/pnas.251438898] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2001] [Indexed: 11/18/2022] Open
Abstract
A general approach to site-specific insertion of amino acid analogues into proteins in vivo would be the import into cells of a suppressor tRNA aminoacylated with the analogue of choice. The analogue would be inserted at any site in the protein specified by a stop codon in the mRNA. The only requirement is that the suppressor tRNA must not be a substrate for any of the cellular aminoacyl-tRNA synthetases. Here, we describe conditions for the import of amber and ochre suppressor tRNAs derived from Escherichia coli initiator tRNA into mammalian COS1 cells, and we present evidence for their activity in the specific suppression of amber (UAG) and ochre (UAA) codons, respectively. We show that an aminoacylated amber suppressor tRNA (supF) derived from the E. coli tyrosine tRNA can be imported into COS1 cells and acts as a suppressor of amber codons, whereas the same suppressor tRNA imported without prior aminoacylation does not, suggesting that the supF tRNA is not a substrate for any mammalian aminoacyl-tRNA synthetase. These results open the possibility of using the supF tRNA aminoacylated with an amino acid analogue as a general approach for the site-specific insertion of amino acid analogues into proteins in mammalian cells. We discuss the possibility further of importing a mixture of amber and ochre suppressor tRNAs for the insertion of two different amino acid analogues into a protein and the potential use of suppressor tRNA import for treatment of some of the human genetic diseases caused by nonsense mutations.
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Affiliation(s)
- C Köhrer
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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20
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Kowal AK, Kohrer C, RajBhandary UL. Twenty-first aminoacyl-tRNA synthetase-suppressor tRNA pairs for possible use in site-specific incorporation of amino acid analogues into proteins in eukaryotes and in eubacteria. Proc Natl Acad Sci U S A 2001; 98:2268-73. [PMID: 11226228 PMCID: PMC30127 DOI: 10.1073/pnas.031488298] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2000] [Indexed: 01/07/2023] Open
Abstract
Two critical requirements for developing methods for the site-specific incorporation of amino acid analogues into proteins in vivo are (i) a suppressor tRNA that is not aminoacylated by any of the endogenous aminoacyl-tRNA synthetases (aaRSs) and (ii) an aminoacyl-tRNA synthetase that aminoacylates the suppressor tRNA but no other tRNA in the cell. Here we describe two such aaRS-suppressor tRNA pairs, one for use in the yeast Saccharomyces cerevisiae and another for use in Escherichia coli. The "21st synthetase-tRNA pairs" include E. coli glutaminyl-tRNA synthetase (GlnRS) along with an amber suppressor derived from human initiator tRNA, for use in yeast, and mutants of the yeast tyrosyl-tRNA synthetase (TyrRS) along with an amber suppressor derived from E. coli initiator tRNA, for use in E. coli. The suppressor tRNAs are aminoacylated in vivo only in the presence of the heterologous aaRSs, and the aminoacylated tRNAs function efficiently in suppression of amber codons. Plasmids carrying the E. coli GlnRS gene can be stably maintained in yeast. However, plasmids carrying the yeast TyrRS gene could not be stably maintained in E. coli. This lack of stability is most likely due to the fact that the wild-type yeast TyrRS misaminoacylates the E. coli proline tRNA. By using error-prone PCR, we have isolated and characterized three mutants of yeast TyrRS, which can be stably expressed in E. coli. These mutants still aminoacylate the suppressor tRNA essentially quantitatively in vivo but show increased discrimination in vitro for the suppressor tRNA over the E. coli proline tRNA by factors of 2.2- to 6.8-fold.
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Affiliation(s)
- A K Kowal
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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21
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Li Y, Ramesh V, Mangroo D, Taneja C, RajBhandary UL. Suppressor mutations in Escherichia coli methionyl-tRNA formyltransferase that compensate for the formylation defect of a mutant tRNA aminoacylated with lysine. Biochemistry 2000; 39:8039-46. [PMID: 10891086 DOI: 10.1021/bi000625+] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The specific formylation of initiator methionyl-tRNA by methionyl-tRNA formyltransferase (MTF) is important for the initiation of protein synthesis in eubacteria such as Escherichia coli. In addition to the determinants for formylation present in the initiator tRNA, the nature of the amino acid attached to the tRNA is also important for formylation. We showed previously that a mutant tRNA aminoacylated with lysine was an extremely poor substrate for formylation. As a consequence, it was essentially inactive in initiation of protein synthesis in E. coli. In contrast, the same tRNA, when aminoacylated with methionine, was a good substrate for formylation and was, consequently, quite active in initiation. Here, we report on the isolation of suppressor mutations in MTF which compensate for the formylation defect of the mutant tRNA aminoacylated with lysine. The suppressor mutant has glycine 178 changed to glutamic acid. Mutants with glycine 178 of MTF changed to aspartic acid, lysine, and leucine were generated and were found to be progressively weaker suppressors. Studies on allele specificity of suppression using different mutant tRNAs as substrates suggest that the Gly178 to Glu mutation compensates for the nature of the amino acid attached to the tRNA. We discuss these results in the framework of the crystal structure of the MTF.fMet-tRNA complex published recently.
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Affiliation(s)
- Y Li
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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22
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Thanedar S, Kumar NV, Varshney U. The fate of the initiator tRNAs is sensitive to the critical balance between interacting proteins. J Biol Chem 2000; 275:20361-7. [PMID: 10748005 DOI: 10.1074/jbc.m001238200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Formylation of the initiator tRNA is essential for normal growth of Escherichia coli. The initiator tRNA containing the U35A36 mutation (CUA anticodon) initiates from UAG codon. However, an additional mutation at position 72 (72A --> G) renders the tRNA (G72/U35A36) inactive in initiation because it is defective in formylation. In this study, we isolated U1G72/U35A36 tRNA containing a wobble base pair at 1-72 positions as an intragenic suppressor of the G72 mutation. The U1G72/U35A36 tRNA is formylated and participates in initiation. More importantly, we show that the mismatch at 1-72 positions of the initiator tRNA, which was thus far thought to be the hallmark of the resistance of this tRNA against peptidyl-tRNA hydrolase (PTH), is not sufficient. The amino acid attached to the initiator tRNA is also important in conferring protection against PTH. Further, we show that the relative levels of PTH and IF2 influence the path adopted by the initiator tRNAs in protein synthesis. These findings provide an important clue to understand the dual function of the single tRNA(Met) in initiation and elongation, in the mitochondria of various organisms.
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Affiliation(s)
- S Thanedar
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560 012, India
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23
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Gite S, Li Y, Ramesh V, RajBhandary UL. Escherichia coli methionyl-tRNA formyltransferase: role of amino acids conserved in the linker region and in the C-terminal domain on the specific recognition of the initiator tRNA. Biochemistry 2000; 39:2218-26. [PMID: 10694387 DOI: 10.1021/bi9926072] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The formylation of initiator methionyl-tRNA by methionyl-tRNA formyltransferase (MTF) is important for the initiation of protein synthesis in eubacteria. We are studying the molecular mechanisms of recognition of the initiator tRNA by Escherichia coli MTF. MTF from eubacteria contains an approximately 100-amino acid C-terminal extension that is not found in the E. coli glycinamide ribonucleotide formyltransferase, which, like MTF, use N(10)-formyltetrahydrofolate as a formyl group donor. This C-terminal extension, which forms a distinct structural domain, is attached to the N-terminal domain through a linker region. Here, we describe the effect of (i) substitution mutations on some nineteen basic, aromatic and other conserved amino acids in the linker region and in the C-terminal domain of MTF and (ii) deletion mutations from the C-terminus on enzyme activity. We show that the positive charge on two of the lysine residues in the linker region leading to the C-terminal domain are important for enzyme activity. Mutation of some of the basic amino acids in the C-terminal domain to alanine has mostly small effects on the kinetic parameters, whereas mutation to glutamic acid has large effects. However, the deletion of 18, 20, or 80 amino acids from the C-terminus has very large effects on enzyme activity. Overall, our results support the notion that the basic amino acid residues in the C-terminal domain provide a positively charged channel that is used for the nonspecific binding of tRNA, whereas some of the amino acids in the linker region play an important role in activity of MTF.
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Affiliation(s)
- S Gite
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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24
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Newton DT, Mangroo D. Mapping the active site of the Haemophilus influenzae methionyl-tRNA formyltransferase: residues important for catalysis and tRNA binding. Biochem J 1999; 339 ( Pt 1):63-9. [PMID: 10085228 PMCID: PMC1220128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Formylation of the initiator methionyl-tRNA by methionyl-tRNA formyltransferase (MTF) is an essential step in initiation of protein synthesis in eubacteria. Here, site-directed mutagenesis was used to identify active site residues of the Haemophilus influenzae MTF. Of the nine residues investigated, only Arg-41, Asn-107, His-109 and Asp-145 were important for the function of the H. influenzae MTF. Replacement of these residues with Ala resulted in a significant reduction in the efficiency of catalysis. Intrinsic fluorescence analysis indicated that this was not due to a defect in N10-formyltetrahydrofolate (fTHF) binding. The Asp-145 and Arg-41 mutations reduced the affinity of the enzyme for the initiator tRNA, whereas the Asn-107 and His-109 mutations affected catalysis but not tRNA binding. Replacement of Arg-41, His-109 and Asp-145 with functionally similar residues also affected the activity of the enzyme. The data suggest that Asn-107, His-109 and Asp-145 are catalytic residues, whereas Arg-41 is involved in tRNA recognition. In the Escherichia coli glycinamide ribonucleotide formyltransferase, which also uses fTHF as the formyl donor, Asn-106, His-108 and Asp-144 participate in the catalytic step. Together, these observations imply that this group of enzymes uses the same basic mechanism in formylating their substrates.
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Affiliation(s)
- D T Newton
- Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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25
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Ramesh V, Mayer C, Dyson MR, Gite S, RajBhandary UL. Induced fit of a peptide loop of methionyl-tRNA formyltransferase triggered by the initiator tRNA substrate. Proc Natl Acad Sci U S A 1999; 96:875-80. [PMID: 9927661 PMCID: PMC15318 DOI: 10.1073/pnas.96.3.875] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A 16-aa insertion loop present in eubacterial methionyl-tRNA formyltransferases (MTF) is critical for specific recognition of the initiator tRNA in Escherichia coli. We have studied the interactions between this region of the E. coli enzyme and initiator methionyl-tRNA (Met-tRNA) by using two complementary protection experiments: protection of MTF against proteolytic cleavage by tRNA and protection of tRNA against nucleolytic cleavage by MTF. The insertion loop in MTF is uniquely sensitive to cleavage by trypsin. We show that the substrate initiator Met-tRNA protects MTF against trypsin cleavage, whereas a formylation-defective mutant initiator Met-tRNA, which binds to MTF with approximately the same affinity, does not. Also, mutants of MTF within the insertion loop (which are defective in formylation) are not protected by the initiator Met-tRNA. Thus, a functional enzyme-substrate complex is necessary for protection of MTF against trypsin cleavage. Along with other data, these results strongly suggest that a segment of the insertion loop, which is exposed and unstructured in MTF, undergoes an induced fit in the functional MTF.Met-tRNA complex but not in the nonfunctional one. Footprinting experiments show that MTF specifically protects the acceptor stem and the 3'-end region of the initiator Met-tRNA against cleavage by double and single strand-specific nucleases. This protection also depends on formation of a functional MTF.Met-tRNA complex. Thus, the insertion loop interacts mostly with the acceptor stem of the initiator Met-tRNA, which contains the critical determinants for formylation.
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Affiliation(s)
- V Ramesh
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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26
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Ramesh V, Gite S, RajBhandary UL. Functional interaction of an arginine conserved in the sixteen amino acid insertion module of Escherichia coli methionyl-tRNA formyltransferase with determinants for formylation in the initiator tRNA. Biochemistry 1998; 37:15925-32. [PMID: 9843398 DOI: 10.1021/bi981873x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Formylation of initiator methionyl-tRNA by methionyl-tRNA formyltransferase (MTF) is important for initiation of protein synthesis in eubacteria. The determinants for formylation are clustered mostly in the acceptor stem of the initiator tRNA. Previous studies suggested that a 16 amino acid insertion loop, present in all eubacterial MTF's (residues 34-49 in the E. coli enzyme), plays an important role in specific recognition of the initiator tRNA. Here, we have analyzed the effect of site-specific mutations of amino acids within this region. We show that an invariant arginine at position 42 within the loop plays a very important role both in the steps of substrate binding and in catalysis. The kinetic parameters of the R42K and R42L mutant enzymes using acceptor stem mutant initiator tRNAs as substrates suggest that arginine 42 makes functional contacts with the determinants at the 3:70 and possibly also the 2:71 base pairs in the acceptor stem of the initiator tRNA. The kinetic parameters of the G41R/R42L double mutant enzyme are essentially the same as those of R42L mutant, suggesting that the requirement for arginine at position 42 cannot be fulfilled by an arginine at position 41. Along with other data, this result suggests that the insertion loop, which is normally unstructured and flexible, adopts a defined conformation upon binding to the tRNA.
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Affiliation(s)
- V Ramesh
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA
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27
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Ramesh V, Gite S, Li Y, RajBhandary UL. Suppressor mutations in Escherichia coli methionyl-tRNA formyltransferase: role of a 16-amino acid insertion module in initiator tRNA recognition. Proc Natl Acad Sci U S A 1997; 94:13524-9. [PMID: 9391059 PMCID: PMC28339 DOI: 10.1073/pnas.94.25.13524] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The specific formylation of initiator methionyl-tRNA by methionyl-tRNA formyltransferase (MTF; EC 2.1.2.9) is important for the initiation of protein synthesis in eubacteria and in eukaryotic organelles. The determinants for formylation in the tRNA are clustered mostly in the acceptor stem. As part of studies on the molecular mechanism of recognition of the initiator tRNA by MTF, we report here on the isolation and characterization of suppressor mutations in Escherichia coli MTF, which compensate for the formylation defect of a mutant initiator tRNA, lacking a critical determinant in the acceptor stem. We show that the suppressor mutant in MTF has a glycine-41 to arginine change within a 16-amino acid insertion found in MTF from many sources. A mutant with glycine-41 changed to lysine also acts as a suppressor, whereas mutants with changes to aspartic acid, glutamine, and leucine do not. The kinetic parameters of the purified wild-type and mutant Arg-41 and Lys-41 enzymes, determined by using the wild-type and mutant tRNAs as substrates, show that the Arg-41 and Lys-41 mutant enzymes compensate specifically for the strong negative effect of the acceptor stem mutation on formylation. These and other considerations suggest that the 16-amino acid insertion in MTF plays an important role in the specific recognition of the determinants for formylation in the acceptor stem of the initiator tRNA.
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MESH Headings
- Amino Acid Sequence
- Binding Sites/genetics
- Escherichia coli/enzymology
- Escherichia coli/genetics
- Genes, Bacterial
- Hydroxymethyl and Formyl Transferases/genetics
- Hydroxymethyl and Formyl Transferases/metabolism
- Kinetics
- Molecular Sequence Data
- Mutagenesis, Insertional
- Mutagenesis, Site-Directed
- Nucleic Acid Conformation
- RNA, Transfer, Met/chemistry
- RNA, Transfer, Met/genetics
- RNA, Transfer, Met/metabolism
- Sequence Homology, Amino Acid
- Suppression, Genetic
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Affiliation(s)
- V Ramesh
- Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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28
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Wu XQ, RajBhandary UL. Effect of the amino acid attached to Escherichia coli initiator tRNA on its affinity for the initiation factor IF2 and on the IF2 dependence of its binding to the ribosome. J Biol Chem 1997; 272:1891-5. [PMID: 8999877 DOI: 10.1074/jbc.272.3.1891] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We show that the nature of the amino acid in the formylaminoacyl-tRNA influences initiation factor (IF) 2 dependence of its ribosome binding and that this IF2 dependence reflects the relative affinity of the formylaminoacyl-tRNA for the initiation factor IF2. We compared the template-dependent ribosome binding activities, in the presence of initiation factors, of wild type and anticodon sequence mutants of Escherichia coli initiator tRNAs that carry formylmethionine (fMet), formylglutamine (fGln), or formylvaline (fVal). The fGln-tRNA bound less well than fMet-tRNA whereas the fVal-tRNA bound as well as fMet-tRNA. The rate and extent of binding of fGln-tRNA to the ribosome was significantly increased by further addition of purified initiation factor IF2. In contrast, the binding of fVal-tRNA or fMet-tRNA was not affected much by the addition of IF2. Using gel mobility shift assay, we have measured the apparent Kd values of the IF2.formylaminoacyl-tRNA binary complexes. These are 1.8, 3.5, and 10.5 microM for fMet-tRNA, fVal-tRNA, and fGln-tRNA, respectively.
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Affiliation(s)
- X Q Wu
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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29
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Mangroo D, Wu XQ, RajBhandary UL. Escherichia coli initiator tRNA: structure-function relationships and interactions with the translational machinery. Biochem Cell Biol 1995; 73:1023-31. [PMID: 8722017 DOI: 10.1139/o95-109] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We showed previously that the sequence and (or) structural elements important for specifying the many distinctive properties of Escherichia coli initiator tRNA are clustered in the acceptor stem and in the anticodon stem and loop. This paper briefly describes this and reviews the results of some recently published studies on the mutant initiator tRNAs generated during this work. First, we have studied the effect of overproduction of methionyl-tRNA transformylase (MTF) and initiation factors IF2 and IF3 on activity of mutant initiator tRNAs that are defective at specific steps in the initiation pathway. Overproduction of MTF rescued specifically the activity of mutant tRNAs defective in formylation but not mutants defective in binding to the P site. Overproduction of IF2 increased the activity of all mutant tRNAs having the CUA anticodon but not of mutant tRNA having the GAC anticodon. Overproduction of IF3 had no effect on the activity of any of the mutant tRNAs tested. Second, for functional studies of mutant initiator tRNA in vivo, we used a CAU --> CUA anticodon sequence mutant that can initiate protein synthesis from UAG instead of AUG. In contrast with the wild-type initiator tRNA, the mutant initiator tRNA has a 2-methylthio-N6-isopentenyl adenosine (ms2i6A) base modification next to the anticodon. Interestingly, this base modification is now important for activity of the mutant tRNA in initiation. In a miaA strain of E. coli deficient in biosynthesis of ms2i6A, the mutant initiator tRNA is much less active in initiation. The defect is specifically in binding to the ribosomal P site.
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Affiliation(s)
- D Mangroo
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA
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30
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Affiliation(s)
- U L RajBhandary
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
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Lee CP, Mandal N, Dyson MR, RajBhandary UL. The discriminator base influences tRNA structure at the end of the acceptor stem and possibly its interaction with proteins. Proc Natl Acad Sci U S A 1993; 90:7149-52. [PMID: 8346229 PMCID: PMC47093 DOI: 10.1073/pnas.90.15.7149] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
For many tRNAs, the discriminator base preceding the CCA sequence at the 3' end is important for aminoacylation. We show that the discriminator base influences the stability of the 1.72 base pair onto which it is stacked. Mutations of the discriminator base from adenosine to cytidine or uridine make the cytidine residue in the C1-G72 base pair of mutant Escherichia coli initiator tRNAs more reactive toward sodium bisulfite, the single-strand-specific reagent. The activity of the enzyme Met-tRNA transformylase toward these and other mutant initiator tRNAs is also consistent with destabilization of the 1.72 base pair in vitro and in vivo. By influencing the strength of the 1.72 base pair, the discriminator base could affect the energetic cost of opening the base pair and modulate the structure of the tRNA near the site of aminoacylation. For some aminoacyl-tRNA synthetases and other proteins that interact with tRNA, these factors could be important for specific recognition and/or formation of the transition state during catalysis.
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Affiliation(s)
- C P Lee
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139-4307
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Dyson MR, Mandal N, RajBhandary UL. Relationship between the structure and function of Escherichia coli initiator tRNA. Biochimie 1993; 75:1051-60. [PMID: 7515283 DOI: 10.1016/0300-9084(93)90004-c] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Through functional studies of mutant tRNAs, we have identified sequence and/or structural features important for specifying the many distinctive properties of E coli initiator tRNA. Many of the mutant tRNAs contain an anticodon sequence change from CAU-->CUA and are now substrates for E coli glutaminyl-tRNA synthetase (GlnRS). We describe here the effect of further mutating the discriminator base 73 and nucleotide 72 at the end of the acceptor stem on: i) recognition of the mutant tRNAs by E coli GlnRS; ii) recognition by E coli methionyl-tRNA transformylase; and iii) activity of the mutant tRNAs in initiation in E coli. For GlnRS recognition, our results are, in general, consistent with interactions found in the crystal structure of the E coli GlnRS-glutamine tRNA complex. The results also support our previous conclusion that formylation of initiator tRNA is important for its function in initiation.
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MESH Headings
- Acyltransferases/chemistry
- Acyltransferases/genetics
- Acyltransferases/metabolism
- Amino Acyl-tRNA Synthetases/chemistry
- Amino Acyl-tRNA Synthetases/genetics
- Amino Acyl-tRNA Synthetases/metabolism
- Base Sequence
- Binding Sites
- Escherichia coli/chemistry
- Escherichia coli/genetics
- Escherichia coli/metabolism
- Hydroxymethyl and Formyl Transferases
- Immunoblotting
- Molecular Sequence Data
- Mutation
- Nucleic Acid Conformation
- Peptide Chain Initiation, Translational
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Transfer, Amino Acyl/chemistry
- RNA, Transfer, Amino Acyl/genetics
- RNA, Transfer, Amino Acyl/metabolism
- RNA, Transfer, Met
- Structure-Activity Relationship
- Substrate Specificity
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Affiliation(s)
- M R Dyson
- Institute of Cell and Molecular Biology, University of Edinburgh, UK
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