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Zeng J, Lu C, Huang X, Li Y. The human eIF4E:4E-BP2 complex structure for studying hyperphosphorylation. Phys Chem Chem Phys 2024; 26:10660-10672. [PMID: 38511550 DOI: 10.1039/d3cp05736d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/22/2024]
Abstract
The cap-dependent mRNA translation is dysregulated in many kinds of cancers. The interaction between eIF4E and eIF4G through a canonical eIF4E-binding motif (CEBM) determines the efficacy of the cap-dependent mRNA translation. eIF4E-binding proteins (4E-BPs) share the CEBM and compete with eIF4G for the same binding surface of eIF4E and then inhibit the mRNA translation. 4E-BPs function as tumor repressors in nature. Hyperphosphorylation of 4E-BPs regulates the structure folding and causes the dissociation of 4E-BPs from eIF4E. However, until now, there has been no structure of the full-length 4E-BPs in complex with eIF4E. The regulation mechanism of phosphorylation is still unclear. In this work, we first investigate the interactions of human eIF4E with the CEBM and an auxiliary eIF4E-binding motif (AEBM) in eIF4G and 4E-BPs. The results unravel that the structure and interactions of the CEBM are highly conserved between eIF4G and 4E-BPs. However, the extended CEBM (ECEBM) in 4E-BPs forms a longer helix than that in eIF4G. The residue R62 in the ECEBM of 4E-BP2 forms salt bridges with E32 and E70 of eIF4E. The residue R63 of 4E-BP2 forms two special hydrogen bonds with N77 of eIF4E. Both of these interactions are missing in eIF4G. The AEBM of 4E-BPs folds into a β-sheet conformation, which protects V81 inside a hydrophobic core in 4E-BP2. In eIF4G, the AEBM exists in a random coil state. The hydrophilic residues S637 and D638 of eIF4G open the hydrophobic core for solvents. The results show that the ECEBM and AEBM may be responsible for the competing advantage of 4E-BP2. Finally, based on our previous work (J. Zeng, F. Jiang and Y. D. Wu, J. Chem. Theory Comput., 2017, 13, 320), the human eIF4E:4E-BP2 complex (eIF4E:BP2P18-I88) including all reported phosphorylation sites is predicted. The eIF4E:BP2P18-I88 complex is different from the existing experimental eIF4E:eIF4G complex and provides an important structure for further studying the regulation mechanism of phosphorylation in 4E-BPs.
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Affiliation(s)
- Juan Zeng
- School of Biomedical Engineering, Guangdong Medical University, Dongguan 523808, China.
| | - CuiMin Lu
- School of Biomedical Engineering, Guangdong Medical University, Dongguan 523808, China.
| | - Xuan Huang
- School of Biomedical Engineering, Guangdong Medical University, Dongguan 523808, China.
| | - Yang Li
- Department of Urology, Huaihe Hospital of Henan University, Kaifeng 475000, Henan, China.
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2
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Gao M, Huang Y. Molecular dynamics simulations revealed topological frustration in the binding-wrapping process of eIF4G with eIF4E. Phys Chem Chem Phys 2024; 26:2073-2081. [PMID: 38131207 DOI: 10.1039/d3cp04899c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
Interaction between the cap-binding protein eIF4E and the scaffolding protein eIF4G is essential for the cap-dependent translation initiation in eukaryotes. In the Saccharomyces cerevisiae eIF4G/eIF4E complex, the intrinsically disordered eIF4E-binding domain of eIF4G folds into a bracelet-like structure upon binding to eIF4E. Aiming to unveil the molecular mechanism underlying the binding-wrapping process of eIF4G with eIF4E, we performed extensive coarse-grained molecular dynamics simulations and transition path analysis in this work. The major transition pathway revealed from our simulations showed that docking of the eIF4E-binding motif of eIF4G to the folded core of eIF4E initiates the binding process and then the disordered eIF4G wraps around the N-terminal tail of eIF4E. Additionally, we identified a minor transition pathway which indicates the involvement of topological frustration in the binding process. By manipulating the interaction strength of the wrapping contacts and the latching contacts, we further dissected factors affecting the formation of topological frustration and the binding transition kinetics. Our findings provide new clues for experimental studies on the binding mechanism of eIF4G to eIF4E in the future and exemplify the involvement of topological frustration in the binding process of intrinsically disordered proteins.
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Affiliation(s)
- Meng Gao
- Hubei Key Laboratory of Industrial Microbiology, Hubei University of Technology, Wuhan 430068, China.
- Cooperative Innovation Center of Industrial Fermentation (Ministry of Education & Hubei Province), Hubei University of Technology, Wuhan 430068, China
- Key Laboratory of Industrial Fermentation (Ministry of Education), Hubei University of Technology, Wuhan 430068, China
| | - Yongqi Huang
- Hubei Key Laboratory of Industrial Microbiology, Hubei University of Technology, Wuhan 430068, China.
- Cooperative Innovation Center of Industrial Fermentation (Ministry of Education & Hubei Province), Hubei University of Technology, Wuhan 430068, China
- Key Laboratory of Industrial Fermentation (Ministry of Education), Hubei University of Technology, Wuhan 430068, China
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3
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Dadwal A, DAS S. Architecture, domain organization, and functional signatures of trypanosomatid keIF4A1s and Plasmodium peIF4A1s suggest conserved functions. J Biosci 2023; 48:44. [PMID: 38018538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2023]
Abstract
Initiation of translation is the first of the three obligatory steps required for protein synthesis and is carried out by a large number of protein factors called initiation factors in conjunction with ribosomes. One of the key conserved protein factors in eukaryotes that plays a role in this process is eIF4A, which has three homologues in humans with eIF4A1 being the primary factor playing a role in translation initiation. eIF4As are members of the family of DEAD-box helicases that carry out different biological functions. eIF4A1s are recruited to translation initiation complexes via association with eIF4G and have ATP binding, ATP hydrolysis, RNA binding, and unwinding activities. Plasmodium and trypanosomatids such as Leishmania and Trypanosoma are parasites that cause human disease. While mechanistically the function of eIF4A1s in eukaryotes is wellunderstood, the orthologues peIF4A1s and keIF4A1s in Plasmodium and trypanosomatids are not well-studied. Here, we have used bioinformatics tools and homology modelling/structure prediction to study the motifs and functional signatures of Plasmodium and trypanosomatid peIF4A1s/keIF4A1s. We report a high degree of sequence conservation, structural conservation, and conservation of protein-protein interaction signatures of Plasmodium and trypanosomatid peIF4A1s/keIF4A1s in comparison with human eIF4A1. Thus, in spite of the great divergence in evolution between these parasites and higher eukaryotes, there is remarkable conservation of motifs and functional signatures in Plasmodium and trypanosomatid peIF4A1s/keIF4A1s.
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Affiliation(s)
- Anica Dadwal
- Infection and Immunology, Translational Health Science and Technology Institute, Faridabad 121 001, India
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4
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Lai WJC, Zhu M, Belinite M, Ballard G, Mathews DH, Ermolenko DN. Intrinsically Unstructured Sequences in the mRNA 3' UTR Reduce the Ability of Poly(A) Tail to Enhance Translation. J Mol Biol 2022; 434:167877. [PMID: 36368412 PMCID: PMC9750134 DOI: 10.1016/j.jmb.2022.167877] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 09/27/2022] [Accepted: 11/01/2022] [Indexed: 11/09/2022]
Abstract
The 5' cap and 3' poly(A) tail of mRNA are known to synergistically stimulate translation initiation via the formation of the cap•eIF4E•eIF4G•PABP•poly(A) complex. Most mRNA sequences have an intrinsic propensity to fold into extensive intramolecular secondary structures that result in short end-to-end distances. The inherent compactness of mRNAs might stabilize the cap•eIF4E•eIF4G•PABP•poly(A) complex and enhance cap-poly(A) translational synergy. Here, we test this hypothesis by introducing intrinsically unstructured sequences into the 5' or 3' UTRs of model mRNAs. We found that the introduction of unstructured sequences into the 3' UTR, but not the 5' UTR, decreases mRNA translation in cell-free wheat germ and yeast extracts without affecting mRNA stability. The observed reduction in protein synthesis results from the diminished ability of the poly(A) tail to stimulate translation. These results suggest that base pair formation by the 3' UTR enhances the cap-poly(A) synergy in translation initiation.
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Affiliation(s)
- Wan-Jung C Lai
- Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, United States
| | - Mingyi Zhu
- Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, United States
| | - Margarita Belinite
- Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, United States
| | - Gregory Ballard
- Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, United States
| | - David H Mathews
- Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, United States
| | - Dmitri N Ermolenko
- Department of Biochemistry & Biophysics and Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642, United States.
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5
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Das S. Analysis of domain organization and functional signatures of trypanosomatid keIF4Gs. Mol Cell Biochem 2022; 477:2415-2431. [PMID: 35585276 DOI: 10.1007/s11010-022-04464-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Accepted: 05/02/2022] [Indexed: 11/25/2022]
Abstract
Translation initiation is the first step in three essential processes leading to protein synthesis. It is carried out by proteins called translation initiation factors and ribosomes on the mRNA. One of the critical translation initiation factors in eukaryotes is eIF4G which is a scaffold protein that helps assemble translation initiation complexes that carry out translation initiation which ultimately leads to polypeptide synthesis. Trypanosomatids are a large family of kinetoplastids, some of which are protozoan parasites that cause diseases in humans through transmission by vectors. While the protein translation mechanisms in eukaryotes and prokaryotes are well understood, the protein translation factors and mechanisms in trypanosomatids are poorly understood necessitating further studies. Unlike other eukaryotes, trypanosomatids contain five eIF4G orthologues with diversity in length and sequences. Here, I have used bioinformatics tools to look at trypanosomatid keIF4G orthologue sequences and report that there are similarities and considerable differences in their domains/motifs organization and signature amino acid sequences that are required for different functions as compared to human eIF4G. My analysis suggests that there is likely to be considerable diversity and complexity in trypanosomatid keIF4G functions as compared to other eukaryotes.
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Affiliation(s)
- Supratik Das
- Infection and Immunology, Translational Health Science and Technology Institute, Faridabad, Haryana, 121001, India.
- Translational Health Science and Technology Institute, NCR Biotech Science Cluster, 3rd Milestone, Faridabad-Gurgaon Expressway, PO Box #04, Faridabad, Haryana, 121001, India.
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6
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Sanson M, Vu Hong A, Massourides E, Bourg N, Suel L, Amor F, Corre G, Bénit P, Barthélémy I, Blot S, Bigot A, Pinset C, Rustin P, Servais L, Voit T, Richard I, Israeli D. miR-379 links glucocorticoid treatment with mitochondrial response in Duchenne muscular dystrophy. Sci Rep 2020; 10:9139. [PMID: 32499563 PMCID: PMC7272451 DOI: 10.1038/s41598-020-66016-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 05/11/2020] [Indexed: 12/12/2022] Open
Abstract
Duchenne Muscular Dystrophy (DMD) is a lethal muscle disorder, caused by mutations in the DMD gene and affects approximately 1:5000-6000 male births. In this report, we identified dysregulation of members of the Dlk1-Dio3 miRNA cluster in muscle biopsies of the GRMD dog model. Of these, we selected miR-379 for a detailed investigation because its expression is high in the muscle, and is known to be responsive to glucocorticoid, a class of anti-inflammatory drugs commonly used in DMD patients. Bioinformatics analysis predicts that miR-379 targets EIF4G2, a translational factor, which is involved in the control of mitochondrial metabolic maturation. We confirmed in myoblasts that EIF4G2 is a direct target of miR-379, and identified the DAPIT mitochondrial protein as a translational target of EIF4G2. Knocking down DAPIT in skeletal myotubes resulted in reduced ATP synthesis and myogenic differentiation. We also demonstrated that this pathway is GC-responsive since treating mice with dexamethasone resulted in reduced muscle expression of miR-379 and increased expression of EIF4G2 and DAPIT. Furthermore, miR-379 seric level, which is also elevated in the plasma of DMD patients in comparison with age-matched controls, is reduced by GC treatment. Thus, this newly identified pathway may link GC treatment to a mitochondrial response in DMD.
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Affiliation(s)
- M Sanson
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France
| | - A Vu Hong
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France
| | | | - N Bourg
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France
| | - L Suel
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France
| | - F Amor
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France
| | - G Corre
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France
| | - P Bénit
- INSERM, UMR S1141, Hôpital Robert Debré, Paris, France
| | - I Barthélémy
- Inserm U955-E10, IMRB, Université Paris Est, Ecole nationale vétérinaire d'Alfort, 94700, Maisons-Alfort, France
| | - S Blot
- Inserm U955-E10, IMRB, Université Paris Est, Ecole nationale vétérinaire d'Alfort, 94700, Maisons-Alfort, France
| | - A Bigot
- Center for Research in Myology UMRS974, Sorbonne Université, INSERM, Myology Institute, Paris, France
| | - C Pinset
- ISTEM, Inserm UMR 861, Evry, France
| | - P Rustin
- INSERM, UMR S1141, Hôpital Robert Debré, Paris, France
| | - L Servais
- MDUK Oxford Neuromuscular Centre, Department of Paediatrics, University of Oxford, Oxford, UK
- Division of Child Neurology, Centre de Références des Maladies Neuromusculaires, Department of Pediatrics, University Hospital Liège & University of Liège, Liège, Belgium
| | - T Voit
- NIHR Great Ormond Street Hospital Biomedical Research Centre and Great Ormond Street Institute of Child Health, University College London, London, UK
| | - I Richard
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France
| | - D Israeli
- Généthon INSERM, UMR_S951, INTEGRARE research unit, Evry, 91000, France.
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7
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Alekhina OM, Terenin IM, Dmitriev SE, Vassilenko KS. Functional Cyclization of Eukaryotic mRNAs. Int J Mol Sci 2020; 21:ijms21051677. [PMID: 32121426 PMCID: PMC7084953 DOI: 10.3390/ijms21051677] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 02/24/2020] [Accepted: 02/27/2020] [Indexed: 11/16/2022] Open
Abstract
The closed-loop model of eukaryotic translation states that mRNA is circularized by a chain of the cap-eIF4E-eIF4G-poly(A)-binding protein (PABP)-poly(A) interactions that brings 5' and 3' ends together. This circularization is thought to promote the engagement of terminating ribosomes to a new round of translation at the same mRNA molecule, thus enhancing protein synthesis. Despite the general acceptance and the elegance of the hypothesis, it has never been proved experimentally. Using continuous in situ monitoring of luciferase synthesis in a mammalian in vitro system, we show here that the rate of translation initiation at capped and polyadenylated reporter mRNAs increases after the time required for the first ribosomes to complete mRNA translation. Such acceleration strictly requires the presence of a poly(A)-tail and is abrogated by the addition of poly(A) RNA fragments or m7GpppG cap analog to the translation reaction. The optimal functional interaction of mRNA termini requires 5' untranslated region (UTR) and 3' UTR of moderate lengths and provides stronger acceleration, thus a longer poly(A)-tail. Besides, we revealed that the inhibitory effect of the dominant negative R362Q mutant of initiation factor eIF4A diminishes in the course of translation reaction, suggesting a relaxed requirement for ATP. Taken together, our results imply that, upon the functional looping of an mRNA, the recycled ribosomes can be recruited to the start codon of the same mRNA molecule in an eIF4A-independent fashion. This non-canonical closed-loop assisted reinitiation (CLAR) mode provides efficient translation of the functionally circularized mRNAs.
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Affiliation(s)
- Olga M. Alekhina
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, 142290 Moscow, Russia;
- Federal Research and Clinical Center of Physical-Chemical Medicine, Federal Medical Biological Agency, 119435 Moscow, Russia
| | - Ilya M. Terenin
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119234 Moscow, Russia;
- Sechenov First Moscow State Medical University, Institute of Molecular Medicine, 119991 Moscow, Russia
| | - Sergey E. Dmitriev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119234 Moscow, Russia;
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 119991 Moscow, Russia
- School of Bioengineering and Bioinformatics, Lomonosov Moscow State University, 119234 Moscow, Russia
- Correspondence: (S.E.D.); (K.S.V.); Tel.: +7-903-2220066 (S.E.D.); +7-496-7318232 (K.S.V.)
| | - Konstantin S. Vassilenko
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, 142290 Moscow, Russia;
- Correspondence: (S.E.D.); (K.S.V.); Tel.: +7-903-2220066 (S.E.D.); +7-496-7318232 (K.S.V.)
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8
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Camillo dos Santos LP, de Matos BM, de Maman Ribeiro BC, Zanchin NIT, Guimarães BG. Crystal structure of the MIF4G domain of the Trypanosoma cruzi translation initiation factor EIF4G5. Acta Crystallogr F Struct Biol Commun 2019; 75:738-743. [PMID: 31797815 PMCID: PMC6891579 DOI: 10.1107/s2053230x19015061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Accepted: 11/07/2019] [Indexed: 11/10/2022] Open
Abstract
Kinetoplastida, a class of early-diverging eukaryotes that includes pathogenic Trypanosoma and Leishmania species, display key differences in their translation machinery compared with multicellular eukaryotes. One of these differences involves a larger number of genes encoding eIF4E and eIF4G homologs and the interaction pattern between the translation initiation factors. eIF4G is a scaffold protein which interacts with the mRNA cap-binding factor eIF4E, the poly(A)-binding protein, the RNA helicase eIF4A and the eIF3 complex. It contains the so-called middle domain of eIF4G (MIF4G), a multipurpose adaptor involved in different protein-protein and protein-RNA complexes. Here, the crystal structure of the MIF4G domain of T. cruzi EIF4G5 is described at 2.4 Å resolution, which is the first three-dimensional structure of a trypanosomatid MIF4G domain to be reported. Structural comparison with IF4G homologs from other eukaryotes and other MIF4G-containing proteins reveals differences that may account for the specific interaction mechanisms of MIF4G despite its highly conserved overall fold.
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Affiliation(s)
- Lucca Pietro Camillo dos Santos
- Carlos Chagas Institute, Oswaldo Cruz Foundation, Curitiba, Paraná, Brazil
- Biosciences and Biotechnology Postgraduate Program, Carlos Chagas Institute, Curitiba, Paraná, Brazil
| | - Bruno Moisés de Matos
- Carlos Chagas Institute, Oswaldo Cruz Foundation, Curitiba, Paraná, Brazil
- Biochemistry Postgraduate Program, Federal University of Paraná, Curitiba, Paraná, Brazil
| | | | | | - Beatriz Gomes Guimarães
- Carlos Chagas Institute, Oswaldo Cruz Foundation, Curitiba, Paraná, Brazil
- Biosciences and Biotechnology Postgraduate Program, Carlos Chagas Institute, Curitiba, Paraná, Brazil
- Biochemistry Postgraduate Program, Federal University of Paraná, Curitiba, Paraná, Brazil
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9
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Gallagher EE, Song JM, Menon A, Mishra LD, Chmiel AF, Garner AL. Consideration of Binding Kinetics in the Design of Stapled Peptide Mimics of the Disordered Proteins Eukaryotic Translation Initiation Factor 4E-Binding Protein 1 and Eukaryotic Translation Initiation Factor 4G. J Med Chem 2019; 62:4967-4978. [PMID: 31033289 PMCID: PMC6679956 DOI: 10.1021/acs.jmedchem.9b00068] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Protein disorder plays a crucial role in signal transduction and is key for many cellular processes including transcription, translation, and cell cycle. Within the intrinsically disordered protein interactome, the α-helix is commonly used for binding, which is induced via a disorder-to-order transition. Because the targeting of protein-protein interactions (PPIs) remains an important challenge in medicinal chemistry, efforts have been made to mimic this secondary structure for rational inhibitor design through the use of stapled peptides. Cap-dependent mRNA translation is regulated by two disordered proteins, 4E-BP1 and eIF4G, that inhibit or stimulate the activity of the m7G cap-binding translation initiation factor, eIF4E, respectively. Both use an α-helical motif for eIF4E binding, warranting the investigation of stapled peptide mimics for manipulating eIF4E PPIs. Herein, we describe our efforts toward this goal, resulting in the synthesis of a cell-active stapled peptide for further development in manipulating aberrant cap-dependent translation in human diseases.
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Affiliation(s)
- Erin E Gallagher
- Department of Medicinal Chemistry, College of Pharmacy , University of Michigan , 1600 Huron Parkway, NCRC B520 , Ann Arbor , Michigan 48109 , United States
| | - James M Song
- Program in Chemical Biology , University of Michigan , 210 Washtenaw Avenue , Ann Arbor , Michigan 48109 , United States
| | - Arya Menon
- Department of Medicinal Chemistry, College of Pharmacy , University of Michigan , 1600 Huron Parkway, NCRC B520 , Ann Arbor , Michigan 48109 , United States
| | - Lauren D Mishra
- Department of Medicinal Chemistry, College of Pharmacy , University of Michigan , 1600 Huron Parkway, NCRC B520 , Ann Arbor , Michigan 48109 , United States
| | - Alyah F Chmiel
- Department of Medicinal Chemistry, College of Pharmacy , University of Michigan , 1600 Huron Parkway, NCRC B520 , Ann Arbor , Michigan 48109 , United States
| | - Amanda L Garner
- Department of Medicinal Chemistry, College of Pharmacy , University of Michigan , 1600 Huron Parkway, NCRC B520 , Ann Arbor , Michigan 48109 , United States
- Program in Chemical Biology , University of Michigan , 210 Washtenaw Avenue , Ann Arbor , Michigan 48109 , United States
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10
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Miras M, Truniger V, Silva C, Verdaguer N, Aranda MA, Querol-Audí J. Structure of eIF4E in Complex with an eIF4G Peptide Supports a Universal Bipartite Binding Mode for Protein Translation. Plant Physiol 2017; 174:1476-1491. [PMID: 28522457 PMCID: PMC5490897 DOI: 10.1104/pp.17.00193] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 05/15/2017] [Indexed: 05/20/2023]
Abstract
The association-dissociation of the cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) with eIF4G is a key control step in eukaryotic translation. The paradigm on the eIF4E-eIF4G interaction states that eIF4G binds to the dorsal surface of eIF4E through a single canonical alpha-helical motif, while metazoan eIF4E-binding proteins (m4E-BPs) advantageously compete against eIF4G via bimodal interactions involving this canonical motif and a second noncanonical motif of the eIF4E surface. Metazoan eIF4Gs share this extended binding interface with m4E-BPs, with significant implications on the understanding of translation regulation and the design of therapeutic molecules. Here we show the high-resolution structure of melon (Cucumis melo) eIF4E in complex with a melon eIF4G peptide and propose the first eIF4E-eIF4G structural model for plants. Our structural data together with functional analyses demonstrate that plant eIF4G binds to eIF4E through both the canonical and noncanonical motifs, similarly to metazoan eIF4E-eIF4G complexes. As in the case of metazoan eIF4E-eIF4G, this may have very important practical implications, as plant eIF4E-eIF4G is also involved in a significant number of plant diseases. In light of our results, a universal eukaryotic bipartite mode of binding to eIF4E is proposed.
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Affiliation(s)
- Manuel Miras
- Centro de Edafología y Biología Aplicada del Segura (CEBAS), Consejo Superior de Investigaciones Científicas (CSIC), 30100 Espinardo, Murcia, Spain
| | - Verónica Truniger
- Centro de Edafología y Biología Aplicada del Segura (CEBAS), Consejo Superior de Investigaciones Científicas (CSIC), 30100 Espinardo, Murcia, Spain
| | - Cristina Silva
- Institut de Biologia Molecular de Barcelona/CSIC, Parc Científic de Barcelona, 08028 Barcelona, Spain
| | - Núria Verdaguer
- Institut de Biologia Molecular de Barcelona/CSIC, Parc Científic de Barcelona, 08028 Barcelona, Spain
| | - Miguel A Aranda
- Centro de Edafología y Biología Aplicada del Segura (CEBAS), Consejo Superior de Investigaciones Científicas (CSIC), 30100 Espinardo, Murcia, Spain
| | - Jordi Querol-Audí
- Institut de Biologia Molecular de Barcelona/CSIC, Parc Científic de Barcelona, 08028 Barcelona, Spain
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11
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Roberts R, Mayberry LK, Browning KS, Rakotondrafara AM. The Triticum Mosaic Virus 5' Leader Binds to Both eIF4G and eIFiso4G for Translation. PLoS One 2017; 12:e0169602. [PMID: 28046134 PMCID: PMC5207729 DOI: 10.1371/journal.pone.0169602] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Accepted: 12/18/2016] [Indexed: 11/19/2022] Open
Abstract
We recently identified a remarkably strong (739 nt-long) IRES-like element in the 5' untranslated region (UTR) of Triticum mosaic virus (TriMV, Potyviridae). Here, we define the components of the cap-binding translation initiation complex that are required for TriMV translation. Using bio-layer interferometry and affinity capture of the native translation apparatus, we reveal that the viral translation element has a ten-fold greater affinity for the large subunit eIF4G/eIFiso4G than to the cap binding protein eIF4E/eIFiso4E. This data supports a translation mechanism that is largely dependent on eIF4G and its isoform. The binding of both scaffold isoforms requires an eight base-pair-long hairpin structure located 270 nucleotides upstream of the translation initiation site, which we have previously shown to be crucial for IRES activity. Despite a weak binding affinity to the mRNA, eIFiso4G alone or in combination with eIFiso4E supports TriMV translation in a cap-binding factor-depleted wheat germ extract. Notably, TriMV 5' UTR-mediated translation is dependent upon eIF4A helicase activity, as the addition of the eIF4A inhibitor hippuristanol inhibits 5' UTR-mediated translation. This inhibition is reversible with the addition of recombinant wheat eIF4A. These results and previous observations demonstrate a key role of eIF4G and eIF4A in this unique mechanism of cap-independent-translation. This work provides new insights into the lesser studied translation mechanisms of plant virus-mediated internal translation initiation.
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Affiliation(s)
- Robyn Roberts
- Department of Plant Pathology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Laura K. Mayberry
- Department of Molecular Biosciences, University of Texas Austin, Austin, Texas, United States of America
| | - Karen S. Browning
- Department of Plant Pathology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Aurélie M. Rakotondrafara
- Department of Molecular Biosciences, University of Texas Austin, Austin, Texas, United States of America
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12
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Edmonds KA, Wagner G. (1)H, (13)C, and (15)N backbone and sidechain chemical shift assignments for the HEAT2 domain of human eIF4GI. Biomol NMR Assign 2015; 9:157-160. [PMID: 24929364 PMCID: PMC4268090 DOI: 10.1007/s12104-014-9564-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2014] [Accepted: 06/07/2014] [Indexed: 06/03/2023]
Abstract
The translation initiation factor eIF4G is required for the translation of many eukaryotic messenger RNAs. Its interaction with the ATP-dependent RNA helicase eIF4A plays an important role in the regulation of translation initiation. eIF4G in humans and other higher eukaryotes contains three HEAT domains, of which HEAT1 and HEAT2 contain binding sites for eIF4A. Here we report the near complete NMR resonance assignment of the 192-residue HEAT2 domain of the human translation initiation factor eIF4GI. The chemical shift data constitute the basis for NMR structural studies aimed at expanding understanding of the role of interactions between the initiation factor eIF4A and eIF4G in translation initiation.
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13
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Joncourt R, Eberle AB, Rufener SC, Mühlemann O. Eukaryotic initiation factor 4G suppresses nonsense-mediated mRNA decay by two genetically separable mechanisms. PLoS One 2014; 9:e104391. [PMID: 25148142 PMCID: PMC4141738 DOI: 10.1371/journal.pone.0104391] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Accepted: 07/08/2014] [Indexed: 11/19/2022] Open
Abstract
Nonsense-mediated mRNA decay (NMD), which is best known for degrading mRNAs with premature termination codons (PTCs), is thought to be triggered by aberrant translation termination at stop codons located in an environment of the mRNP that is devoid of signals necessary for proper termination. In mammals, the cytoplasmic poly(A)-binding protein 1 (PABPC1) has been reported to promote correct termination and therewith antagonize NMD by interacting with the eukaryotic release factors 1 (eRF1) and 3 (eRF3). Using tethering assays in which proteins of interest are recruited as MS2 fusions to a NMD reporter transcript, we show that the three N-terminal RNA recognition motifs (RRMs) of PABPC1 are sufficient to antagonize NMD, while the eRF3-interacting C-terminal domain is dispensable. The RRM1-3 portion of PABPC1 interacts with eukaryotic initiation factor 4G (eIF4G) and tethering of eIF4G to the NMD reporter also suppresses NMD. We identified the interactions of the eIF4G N-terminus with PABPC1 and the eIF4G core domain with eIF3 as two genetically separable features that independently enable tethered eIF4G to inhibit NMD. Collectively, our results reveal a function of PABPC1, eIF4G and eIF3 in translation termination and NMD suppression, and they provide additional evidence for a tight coupling between translation termination and initiation.
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Affiliation(s)
- Raphael Joncourt
- University of Bern, Department of Chemistry and Biochemistry, Bern, Switzerland
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland
| | - Andrea B. Eberle
- University of Bern, Department of Chemistry and Biochemistry, Bern, Switzerland
| | - Simone C. Rufener
- University of Bern, Department of Chemistry and Biochemistry, Bern, Switzerland
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland
| | - Oliver Mühlemann
- University of Bern, Department of Chemistry and Biochemistry, Bern, Switzerland
- * E-mail:
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14
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Akabayov SR, Wagner G. Backbone resonance assignment of the HEAT1-domain of the human eukaryotic translation initiation factor 4GI. Biomol NMR Assign 2014; 8:89-91. [PMID: 23325513 PMCID: PMC3640741 DOI: 10.1007/s12104-013-9459-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 01/04/2013] [Indexed: 06/01/2023]
Abstract
Controlling translation during protein synthesis is crucial for cell proliferation and differentiation. Protein translation is orchestrated by an assembly of various protein components at the ribosomal subunits. The eukaryotic translation initiation factor 4G (eIF4G) plays an important role in the formation of the translation initiation complex eIF4F consisting of eIF4G, the ATP dependent RNA helicase eIF4A and the cap binding protein eIF4E. One of the functions of eIF4G is the enhancement of the activity of eIF4A facilitated mainly through binding to the HEAT1 domain of eIF4G. In order to understand the interaction of HEAT1 with eIF4A and other components during translation initiation backbone assignment is essential. Here we report the (1)H, (13)C and (15)N backbone assignment for the HEAT1 domain of human eIF4G isoform I (eIF4GI-HEAT1), the first of three HEAT domains of eIF4G (29 kDa) as a basis for the elucidation of its structure and interactions with its binding partners, necessary for understanding the mechanism of its biological function.
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Affiliation(s)
- Sabine R Akabayov
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA, 02115, USA
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15
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Mayberry LK, Allen ML, Nitka KR, Campbell L, Murphy PA, Browning KS. Plant cap-binding complexes eukaryotic initiation factors eIF4F and eIFISO4F: molecular specificity of subunit binding. J Biol Chem 2011; 286:42566-42574. [PMID: 21965660 PMCID: PMC3234931 DOI: 10.1074/jbc.m111.280099] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Revised: 09/29/2011] [Indexed: 01/04/2023] Open
Abstract
The initiation of translation in eukaryotes requires a suite of eIFs that include the cap-binding complex, eIF4F. eIF4F is comprised of the subunits eIF4G and eIF4E and often the helicase, eIF4A. The eIF4G subunit serves as an assembly point for other initiation factors, whereas eIF4E binds to the 7-methyl guanosine cap of mRNA. Plants have an isozyme form of eIF4F (eIFiso4F) with comparable subunits, eIFiso4E and eIFiso4G. Plant eIF4A is very loosely associated with the plant cap-binding complexes. The specificity of interaction of the individual subunits of the two complexes was previously unknown. To address this issue, mixed complexes (eIF4E-eIFiso4G or eIFiso4E-eIF4G) were expressed and purified from Escherichia coli for biochemical analysis. The activity of the mixed complexes in in vitro translation assays correlated with the large subunit of the respective correct complex. These results suggest that the eIF4G or eIFiso4G subunits influence translational efficiency more than the cap-binding subunits. The translation assays also showed varying responses of the mRNA templates to eIF4F or eIFiso4F, suggesting that some level of mRNA discrimination is possible. The dissociation constants for the correct complexes have K(D) values in the subnanomolar range, whereas the mixed complexes were found to have K(D) values in the ∼10 nm range. Displacement assays showed that the correct binding partner readily displaces the incorrect binding partner in a manner consistent with the difference in K(D) values. These results show molecular specificity for the formation of plant eIF4F and eIFiso4F complexes and suggest a role in mRNA discrimination during initiation of translation.
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Affiliation(s)
- Laura K Mayberry
- Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712
| | - M Leah Allen
- Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712
| | - Kelley R Nitka
- Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712
| | - Lara Campbell
- Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712
| | - Patricia A Murphy
- Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712
| | - Karen S Browning
- Department of Chemistry and Biochemistry and the Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712.
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16
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Gal M, Edmonds KA, Milbradt AG, Takeuchi K, Wagner G. Speeding up direct (15)N detection: hCaN 2D NMR experiment. J Biomol NMR 2011; 51:497-504. [PMID: 22038648 PMCID: PMC3338130 DOI: 10.1007/s10858-011-9580-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Accepted: 10/11/2011] [Indexed: 05/05/2023]
Abstract
Experiments detecting low gyromagnetic nuclei have recently been proposed to utilize the relatively slow relaxation properties of these nuclei in comparison to (1)H. Here we present a new type of (15)N direct-detection experiment. Like the previously proposed CaN experiment (Takeuchi et al. in J Biomol NMR 47:271-282, 2010), the hCaN experiment described here sequentially connects amide (15)N resonances, but utilizes the initial high polarization and the faster recovery of the (1)H nucleus to shorten the recycling delay. This allows recording 2D (15)N-detected NMR experiments on proteins within a few hours, while still obtaining superior resolution for (13)C and (15)N, establishing sequential assignments through prolines, and at conditions where amide protons exchange rapidly. The experiments are demonstrated on various biomolecules, including the small globular protein GB1, the 22 kDa HEAT2 domain of eIF4G, and an unstructured polypeptide fragment of NFAT1, which contains many SerPro sequence repeats.
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Affiliation(s)
- Maayan Gal
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Katherine A. Edmonds
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Alexander G. Milbradt
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Koh Takeuchi
- Biomedicinal Information Research Center, National institute of Advanced Industrial Science and Technology, Tokyo 135-0064, Japan
| | - Gerhard Wagner
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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17
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Santiveri CM, Mirassou Y, Rico-Lastres P, Martínez-Lumbreras S, Pérez-Cañadillas JM. Pub1p C-terminal RRM domain interacts with Tif4631p through a conserved region neighbouring the Pab1p binding site. PLoS One 2011; 6:e24481. [PMID: 21931728 PMCID: PMC3169606 DOI: 10.1371/journal.pone.0024481] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Accepted: 08/11/2011] [Indexed: 11/18/2022] Open
Abstract
Pub1p, a highly abundant poly(A)+ mRNA binding protein in Saccharomyces cerevisiae, influences the stability and translational control of many cellular transcripts, particularly under some types of environmental stresses. We have studied the structure, RNA and protein recognition modes of different Pub1p constructs by NMR spectroscopy. The structure of the C-terminal RRM domain (RRM3) shows a non-canonical N-terminal helix that packs against the canonical RRM fold in an original fashion. This structural trait is conserved in Pub1p metazoan homologues, the TIA-1 family, defining a new class of RRM-type domains that we propose to name TRRM (TIA-1 C-terminal domain-like RRM). Pub1p TRRM and the N-terminal RRM1-RRM2 tandem bind RNA with high selectivity for U-rich sequences, with TRRM showing additional preference for UA-rich ones. RNA-mediated chemical shift changes map to β-sheet and protein loops in the three RRMs. Additionally, NMR titration and biochemical in vitro cross-linking experiments determined that Pub1p TRRM interacts specifically with the N-terminal region (1-402) of yeast eIF4G1 (Tif4631p), very likely through the conserved Box1, a short sequence motif neighbouring the Pab1p binding site in Tif4631p. The interaction involves conserved residues of Pub1p TRRM, which define a protein interface that mirrors the Pab1p-Tif4631p binding mode. Neither protein nor RNA recognition involves the novel N-terminal helix, whose functional role remains unclear. By integrating these new results with the current knowledge about Pub1p, we proposed different mechanisms of Pub1p recruitment to the mRNPs and Pub1p-mediated mRNA stabilization in which the Pub1p/Tif4631p interaction would play an important role.
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Affiliation(s)
- Clara M. Santiveri
- Department of Biological Physical Chemistry, Instituto de Química-Física “Rocasolano”, CSIC, Madrid, Spain
| | - Yasmina Mirassou
- Department of Biological Physical Chemistry, Instituto de Química-Física “Rocasolano”, CSIC, Madrid, Spain
| | - Palma Rico-Lastres
- Department of Biological Physical Chemistry, Instituto de Química-Física “Rocasolano”, CSIC, Madrid, Spain
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18
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Waters LC, Strong SL, Ferlemann E, Oka O, Muskett FW, Veverka V, Banerjee S, Schmedt T, Henry AJ, Klempnauer KH, Carr MD. Structure of the tandem MA-3 region of Pdcd4 protein and characterization of its interactions with eIF4A and eIF4G: molecular mechanisms of a tumor suppressor. J Biol Chem 2011; 286:17270-80. [PMID: 21454508 PMCID: PMC3089569 DOI: 10.1074/jbc.m110.166157] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Revised: 03/04/2011] [Indexed: 11/25/2022] Open
Abstract
One of the key regulatory points of translation initiation is recruitment of the 43S preinitation complex to the 5' mRNA cap by the eIF4F complex (eIF4A, eIF4E, and eIF4G). The tumor suppressor protein Pdcd4 has been shown to inhibit cap-dependent translation by interacting tightly with the RNA helicase eIF4A via its tandem MA-3 domains. The NMR studies reported here reveal a fairly extensive and well defined interface between the two MA-3 domains in solution, which appears to be stabilized by a network of interdomain salt bridges and hydrogen bonds, and reveals a unique orientation of the two domains. Characterization of the stoichiometry of the Pdcd4-eIF4A complex suggests that under physiological conditions Pdcd4 binds to a single molecule of eIF4A, which involves contacts with both Pdcd4 MA-3 domains. We also show that contacts mediated by a conserved acidic patch on the middle MA-3 domain of Pdcd4 are essential for forming a tight complex with eIF4A in vivo, whereas the equivalent region of the C-terminal MA-3 domain appears to have no role in complex formation in vivo. The formation of a 1:1 eIF4A-Pdcd4 complex in solution is consistent with the reported presence in vivo of only one molecule of eIF4A in the eIF4F complex. Pdcd4 has also been reported to interact directly with the middle region of eIF4G, however, we were unable to obtain any evidence for even a weak, transient direct interaction.
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Affiliation(s)
- Lorna C. Waters
- From the Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - Sarah L. Strong
- From the Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - Eva Ferlemann
- the Institut für Biochemie, Westfälische-Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 2, D-48149 Münster, Germany, and
| | - Ojore Oka
- From the Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - Frederick W. Muskett
- From the Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - Vaclav Veverka
- From the Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - Sreemoti Banerjee
- From the Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
| | - Thore Schmedt
- the Institut für Biochemie, Westfälische-Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 2, D-48149 Münster, Germany, and
| | - Alistair J. Henry
- Research and Development, UCB-Celltech, Slough SL1 3WE, United Kingdom
| | - Karl-Heinz Klempnauer
- the Institut für Biochemie, Westfälische-Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 2, D-48149 Münster, Germany, and
| | - Mark D. Carr
- From the Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, United Kingdom
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19
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Montpetit B, Thomsen ND, Helmke KJ, Seeliger MA, Berger JM, Weis K. A conserved mechanism of DEAD-box ATPase activation by nucleoporins and InsP6 in mRNA export. Nature 2011; 472:238-42. [PMID: 21441902 PMCID: PMC3078754 DOI: 10.1038/nature09862] [Citation(s) in RCA: 185] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2010] [Accepted: 01/19/2011] [Indexed: 12/25/2022]
Abstract
Superfamily 1 and superfamily 2 RNA helicases are ubiquitous messenger-RNA-protein complex (mRNP) remodelling enzymes that have critical roles in all aspects of RNA metabolism. The superfamily 2 DEAD-box ATPase Dbp5 (human DDX19) functions in mRNA export and is thought to remodel mRNPs at the nuclear pore complex (NPC). Dbp5 is localized to the NPC via an interaction with Nup159 (NUP214 in vertebrates) and is locally activated there by Gle1 together with the small-molecule inositol hexakisphosphate (InsP(6)). Local activation of Dbp5 at the NPC by Gle1 is essential for mRNA export in vivo; however, the mechanistic role of Dbp5 in mRNP export is poorly understood and it is not known how Gle1(InsP6) and Nup159 regulate the activity of Dbp5. Here we report, from yeast, structures of Dbp5 in complex with Gle1(InsP6), Nup159/Gle1(InsP6) and RNA. These structures reveal that InsP(6) functions as a small-molecule tether for the Gle1-Dbp5 interaction. Surprisingly, the Gle1(InsP6)-Dbp5 complex is structurally similar to another DEAD-box ATPase complex essential for translation initiation, eIF4G-eIF4A, and we demonstrate that Gle1(InsP6) and eIF4G both activate their DEAD-box partner by stimulating RNA release. Furthermore, Gle1(InsP6) relieves Dbp5 autoregulation and cooperates with Nup159 in stabilizing an open Dbp5 intermediate that precludes RNA binding. These findings explain how Gle1(InsP6), Nup159 and Dbp5 collaborate in mRNA export and provide a general mechanism for DEAD-box ATPase regulation by Gle1/eIF4G-like activators.
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Affiliation(s)
- Ben Montpetit
- Division of Cell and Developmental Biology, University of California, Berkeley, CA 94720
- Department of Molecular and Cell Biology and QB3 Institute, University of California, Berkeley, CA 94720
| | - Nathan D. Thomsen
- Division of Biochemistry and Molecular Biology, University of California, Berkeley, CA 94720
- Department of Molecular and Cell Biology and QB3 Institute, University of California, Berkeley, CA 94720
| | - Kara J. Helmke
- Division of Cell and Developmental Biology, University of California, Berkeley, CA 94720
- Department of Molecular and Cell Biology and QB3 Institute, University of California, Berkeley, CA 94720
| | - Markus A. Seeliger
- Division of Biochemistry and Molecular Biology, University of California, Berkeley, CA 94720
- Department of Molecular and Cell Biology and QB3 Institute, University of California, Berkeley, CA 94720
| | - James M. Berger
- Division of Biochemistry and Molecular Biology, University of California, Berkeley, CA 94720
- Department of Molecular and Cell Biology and QB3 Institute, University of California, Berkeley, CA 94720
| | - Karsten Weis
- Division of Cell and Developmental Biology, University of California, Berkeley, CA 94720
- Department of Molecular and Cell Biology and QB3 Institute, University of California, Berkeley, CA 94720
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20
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Watanabe R, Murai MJ, Singh CR, Fox S, Ii M, Asano K. The eukaryotic initiation factor (eIF) 4G HEAT domain promotes translation re-initiation in yeast both dependent on and independent of eIF4A mRNA helicase. J Biol Chem 2010; 285:21922-33. [PMID: 20463023 PMCID: PMC2903371 DOI: 10.1074/jbc.m110.132027] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2010] [Revised: 04/30/2010] [Indexed: 11/06/2022] Open
Abstract
Translation re-initiation provides the molecular basis for translational control of mammalian ATF4 and yeast GCN4 mediated by short upstream open reading (uORFs) in response to eIF2 phosphorylation. eIF4G is the major adaptor subunit of eIF4F that binds the cap-binding subunit eIF4E and the mRNA helicase eIF4A and is also required for re-initiation in mammals. Here we show that the yeast eIF4G2 mutations altering eIF4E- and eIF4A-binding sites increase re-initiation at GCN4 and impair recognition of the start codons of uORF1 or uORF4 located after uORF1. The increase in re-initiation at GCN4 was partially suppressed by increasing the distance between uORF1 and GCN4, suggesting that the mutations decrease the migration rate of the scanning ribosome in the GCN4 leader. Interestingly, eIF4E overexpression suppressed both the phenotypes caused by the mutation altering eIF4E-binding site. Thus, eIF4F is required for accurate AUG selection and re-initiation also in yeast, and the eIF4G interaction with the mRNA-cap appears to promote eIF4F re-acquisition by the re-initiating 40 S subunit. However, eIF4A overexpression suppressed the impaired AUG recognition but not the increase in re-initiation caused by the mutations altering eIF4A-binding site. These results not only provide evidence that mRNA unwinding by eIF4A stimulates start codon recognition, but also suggest that the eIF4A-binding site on eIF4G made of the HEAT domain stimulates the ribosomal scanning independent of eIF4A. Based on the RNA-binding activities identified within the unstructured segments flanking the eIF4G2 HEAT domain, we discuss the role of the HEAT domain in scanning beyond loading eIF4A onto the pre-initiation complex.
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Affiliation(s)
- Ryosuke Watanabe
- From the Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506
| | - Marcelo Jun Murai
- From the Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506
| | - Chingakham Ranjit Singh
- From the Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506
| | - Stephanie Fox
- From the Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506
| | - Miki Ii
- From the Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506
| | - Katsura Asano
- From the Molecular, Cellular, and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506
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21
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Cheng S, Gallie DR. eIF4G, eIFiso4G, and eIF4B bind the poly(A)-binding protein through overlapping sites within the RNA recognition motif domains. J Biol Chem 2007; 282:25247-58. [PMID: 17606619 DOI: 10.1074/jbc.m702193200] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The poly(A)-binding protein (PABP), a protein that contains four conserved RNA recognition motifs (RRM1-4) and a C-terminal domain, is expressed throughout the eukaryotic kingdom and promotes translation through physical and functional interactions with eukaryotic initiation factor (eIF) 4G and eIF4B. Two highly divergent isoforms of eIF4G, known as eIF4G and eIFiso4G, are expressed in plants. As little is known about how PABP can interact with RNA and three distinct translation initiation factors in plants, the RNA binding specificity and organization of the protein interaction domains in wheat PABP was investigated. Wheat PABP differs from animal PABP in that its RRM1 does not bind RNA as an individual domain and that RRM 2, 3, and 4 exhibit different RNA binding specificities to non-poly(A) sequences. The PABP interaction domains for eIF4G and eIFiso4G were distinct despite the functional similarity between the eIF4G proteins. A single interaction domain for eIF4G is present in the RRM1 of PABP, whereas eIFiso4G interacts at two sites, i.e. one within RRM1-2 and the second within RRM3-4. The eIFiso4G binding site in RRM1-2 mapped to a 36-amino acid region encompassing the C-terminal end of RRM1, the linker region, and the N-terminal end of RRM2, whereas the second site in RRM3-4 was more complex. A single interaction domain for eIF4B is present within a 32-amino acid region representing the C-terminal end of RRM1 of PABP that overlaps with the N-proximal eIFiso4G interaction domain. eIF4B and eIFiso4G exhibited competitive binding to PABP, supporting the overlapping nature of their interaction domains. These results support the notion that eIF4G, eIFiso4G, and eIF4B interact with distinct molecules of PABP to increase the stability of the interaction between the termini of an mRNA.
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Affiliation(s)
- Shijun Cheng
- Department of Biochemistry, University of California, Riverside, California 92521-0129, USA
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22
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Kapasi P, Chaudhuri S, Vyas K, Baus D, Komar AA, Fox PL, Merrick WC, Mazumder B. L13a blocks 48S assembly: role of a general initiation factor in mRNA-specific translational control. Mol Cell 2007; 25:113-26. [PMID: 17218275 PMCID: PMC1810376 DOI: 10.1016/j.molcel.2006.11.028] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Revised: 10/23/2006] [Accepted: 11/30/2006] [Indexed: 01/30/2023]
Abstract
Transcript-specific translational control restricts macrophage inflammatory gene expression. The proinflammatory cytokine interferon-gamma induces phosphorylation of ribosomal protein L13a and translocation from the 60S ribosomal subunit to the interferon-gamma-activated inhibitor of translation (GAIT) complex. This complex binds the 3'UTR of ceruloplasmin mRNA and blocks its translation. Here, we elucidate the molecular mechanism underlying repression by L13a. Translation of the GAIT element-containing reporter mRNA is sensitive to L13a-mediated silencing when driven by internal ribosome entry sites (IRESs) that require initiation factor eIF4G, but is resistant to silencing when driven by eIF4F-independent IRESs, demonstrating a critical role for eIF4G. Interaction of L13a with eIF4G blocks 43S recruitment without suppressing eIF4F complex formation. eIF4G attack, e.g., by virus, stress, or caspases, is a well-known mechanism of global inhibition of protein synthesis. However, our studies reveal a unique mechanism in which targeting of eIF4G by mRNA-bound L13a elicits transcript-specific translational repression.
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Affiliation(s)
- Purvi Kapasi
- Department of Biological, Geological and Environmental Science, Cleveland State University, Cleveland, Ohio 44115
| | - Sujan Chaudhuri
- Department of Biological, Geological and Environmental Science, Cleveland State University, Cleveland, Ohio 44115
| | - Keyur Vyas
- Department of Biological, Geological and Environmental Science, Cleveland State University, Cleveland, Ohio 44115
| | - Diane Baus
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106
| | - Anton A. Komar
- Department of Biological, Geological and Environmental Science, Cleveland State University, Cleveland, Ohio 44115
| | - Paul L. Fox
- Department of Biological, Geological and Environmental Science, Cleveland State University, Cleveland, Ohio 44115
- Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - William C. Merrick
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106
| | - Barsanjit Mazumder
- Department of Biological, Geological and Environmental Science, Cleveland State University, Cleveland, Ohio 44115
- *Correspondence: E-mail: , Phone: 216-687-2435, Fax: 216-687-2932
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23
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Oulhen N, Salaün P, Cosson B, Cormier P, Morales J. After fertilization of sea urchin eggs, eIF4G is post-translationally modified and associated with the cap-binding protein eIF4E. J Cell Sci 2007; 120:425-34. [PMID: 17213333 DOI: 10.1242/jcs.03339] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Release of eukaryotic initiation factor 4E (eIF4E) from its translational repressor eIF4E-binding protein (4E-BP) is a crucial event for the first mitotic division following fertilization of sea urchin eggs. Finding partners of eIF4E following fertilization is crucial to understand how eIF4E functions during this physiological process. The isolation and characterization of cDNA encoding Sphaerechinus granularis eIF4G (SgIF4G) are reported. mRNA of SgIF4G is present as a single 8.5-kb transcript in unfertilized eggs, suggesting that only one ortholog exists in echinoderms. The longest open reading frame predicts a sequence of 5235 nucleotides encoding a deduced polypeptide of 1745 amino acids with a predicted molecular mass of 192 kDa. Among highly conserved domains, SgIF4G protein possesses motifs that correspond to the poly(A) binding protein and eIF4E protein-binding sites. A specific polyclonal antibody was produced and used to characterize the SgIF4G protein in unfertilized and fertilized eggs by SDS-PAGE and western blotting. Multiple differentially migrating bands representing isoforms of sea urchin eIF4G are present in unfertilized eggs. Fertilization triggers modifications of the SgIF4G isoforms and rapid formation of the SgIF4G-eIF4E complex. Whereas rapamycin inhibits the formation of the SgIF4G-eIF4E complex, modification of these SgIF4G isoforms occurs independently from the rapamycin-sensitive pathway. Microinjection of a peptide corresponding to the eIF4E-binding site derived from the sequence of SgIF4G into unfertilized eggs affects the first mitotic division of sea urchin embryos. Association of SgIF4G with eIF4E is a crucial event for the onset of the first mitotic division following fertilization, suggesting that cap-dependent translation is highly regulated during this process. This hypothesis is strengthened by the evidence that microinjection of the cap analog m(7)GDP into unfertilized eggs inhibits the first mitotic division.
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Affiliation(s)
- Nathalie Oulhen
- Université Pierre et Marie Curie-Paris6, UMR 7150, Equipe Cycle Cellulaire et Développement and CNRS, UMR 7150, Station Biologique de Roscoff, 29682 Roscoff CEDEX, France
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24
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Abstract
The peroxisome proliferator-activated receptor (PPAR) alpha is a member of the nuclear receptor superfamily of ligand-dependent transcription factors related to retinoid, steroid, and thyroid hormone receptors. The aim of the present study is to evaluate the role of PPAR-alpha receptor on the development of multiple-organ dysfunction syndrome (MODS) induced by zymosan. MODS was induced by peritoneal injection of zymosan (dose, 500 mg/kg i.p. as a suspension in saline) in PPAR-alpha wild-type (PPAR-alphaWT) and PPAR-alpha knockout (PPAR-alphaKO) mice, was assessed 18 h after the administration of zymosan, and was monitored for 12 days (for loss of body weight and mortality). A severe inflammatory process, induced by zymosan administration in wild-type mice, coincided with the damage of liver, kidney, pancreas, and small intestine. Myeloperoxidase activity, indicative of neutrophil infiltration, and lipid peroxidation were significantly increased in zymosan-treated wild-type mice. Zymosan in the wild-type mice also induced a significant increase in the plasma levels of nitrite/nitrate. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine and Fas ligand in the intestine of zymosan-treated wild-type mice. In contrast, the degree of (1) peritoneal inflammation and tissue injury, (2) nitrotyrosine formation and Fas ligand expression, and (3) neutrophil infiltration were markedly enhanced in intestinal tissue obtained from zymosan-treated PPAR-alphaKO mice. Zymosan-treated PPAR-alphaKO mice also showed a significantly increased mortality. Taken together, the present study clearly demonstrates that PPAR-alpha pathway modulates the degree of MODS associated with zymosan-induced nonseptic shock.
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Affiliation(s)
- Thomas C Vary
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
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25
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Abstract
Eukaryotic initiation factor (eIF) 4G is an integral member of the translation initiation machinery. The molecule serves as a scaffold for several other initiation factors, including eIF4E, eIF4AI, the eIF3 complex, and poly(A)-binding protein (PABP). Previous work indicates that complexes between these proteins exhibit enhanced mRNA cap-binding and RNA helicase activities relative to the respective individual proteins, eIF4E and eIF4A. The eIF4G-PABP interaction has been implicated in enhancing the formation of 48 S and 80 S initiation complexes and ribosome recycling through mRNA circularization. The eIF3-eIF4GI interaction is believed to forge the link between the 40 S subunit and the mRNA. Here we have investigated the behavior in vitro and in intact cells of eIF4GIf molecules lacking either the PABP-binding site, the eIF3-binding site, the middle domain eIF4A-binding site, or the C-terminal segment that includes the second eIF4A-binding site. Although in some cases the mutant forms were recruited more slowly, all of these eIF4G variants could form complexes with eIF4E, enter 48 S complexes and polysomes in vivo and in vitro, and partially rescue translation in cells targeted with eIF4GI short interfering RNA. In the reticulocyte lysate, eIF4G unable to interact directly with PABP showed little impairment in its ability to support translation, whereas loss of either of the eIF4A-binding sites or the eIF3-binding site resulted in a marked decrease in activity. We conclude that there is considerable redundancy in the mechanisms forming initiation complexes in mammalian cells, such that many individual interactions have regulatory rather than essential roles.
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Affiliation(s)
- Tracey M Hinton
- Department of Biochemistry, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
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26
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Jünemann C, Song Y, Bassili G, Goergen D, Henke J, Niepmann M. Picornavirus internal ribosome entry site elements can stimulate translation of upstream genes. J Biol Chem 2006; 282:132-41. [PMID: 17095505 DOI: 10.1074/jbc.m608750200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Certain viral and cellular mRNAs initiate translation cap-independently at internal ribosome entry site (IRES) elements. Picornavirus IRES elements are widely used in dicistronic or multicistronic vectors in gene therapy, virus replicon systems, and analysis of IRES function. In such vectors, expression of the upstream gene often serves as internal control to standardize the readings of IRES-driven downstream reporter activity. Picornaviral IRES elements translate optimally at up to 120 mM K(+) concentration, whereas genes used as upstream reporters usually have lower salt optima when present in monocistronic mRNAs. However, here we show that such reporter genes are efficiently translated at higher K(+) concentrations when placed upstream of a functional picornavirus IRES. This translation enhancement occurs in cis, is independent of the nature of the first reporter and of second reporter translation, and is conferred by the IRESs of picornaviruses but not of hepatitis C virus. A defective picornavirus IRES with a deletion killing IRES activity but leaving the binding site for initiation factor eIF4G intact retains translation enhancement activity. Translation enhancement on a capped mRNA is disabled by m(7)GDP. In addition, the C-terminal fragment of eIF4G can confer translation enhancement also on uncapped mRNA. We conclude that whenever eIF4F has been captured to a dicistronic mRNA by binding to a picornavirus IRES via its eIF4G moiety, it can be provided in cis to the 5'-end of the RNA and there stimulate translation initiation, either by binding to the cap nucleotide using its eIF4E moiety or by binding to the RNA cap-independently using its eIF4G moiety.
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Affiliation(s)
- Christiane Jünemann
- Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University Giessen, Friedrichstrasse 24, 35392 Giessen, Germany
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27
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Ray S, Yumak H, Domashevskiy A, Khan MA, Gallie DR, Goss DJ. Tobacco etch virus mRNA preferentially binds wheat germ eukaryotic initiation factor (eIF) 4G rather than eIFiso4G. J Biol Chem 2006; 281:35826-34. [PMID: 17012235 DOI: 10.1074/jbc.m605762200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 5'-leader of tobacco etch virus (TEV) genomic RNA directs the efficient translation from the naturally uncapped viral RNA. The TEV 143-nt 5'-leader folds into a structure that contains two domains, each of which contains RNA pseudoknots. The 5'-proximal pseudoknot 1 (PK1) is necessary to promote cap-independent translation (Zeenko, V., and Gallie, D. R. (2005) J. Biol. Chem. 280, 26813-26824). During the translation initiation of cellular mRNAs, eIF4G functions as an adapter that recruits many of the factors involved in stimulating 40 S ribosomal subunit binding to an mRNA. Two related but highly distinct eIF4G proteins are expressed in plants, animals, and yeast. The two plant eIF4G isoforms, referred to as eIF4G and eIFiso4G, differ in size (165 and 86 kDa, respectively) and their functional differences are still unclear. Although eIF4G is required for the translation of TEV mRNA, it is not known if eIF4G binds directly to the TEV RNA itself or if other factors are required. To determine whether binding affinity and isoform preference correlates with translational efficiency, fluorescence spectroscopy was used to measure the binding of eIF4G, eIFiso4G, and their complexes (eIF4F and eIFiso4F, respectively) to the TEV 143-nt 5'-leader (TEV1-143) and a shorter RNA that contained PK1. A mutant (i.e. S1-3) in which the stem of PK1 was disrupted resulting in impaired cap-independent translation, was also tested. These studies demonstrate that eIF4G binds TEV1-143 and PK1 RNA with approximately 22-30-fold stronger affinity than eIFiso4G. eIF4G and eIF4F bind TEV1-143 with similar affinity, whereas eIFiso4F binds with approximately 6-fold higher affinity than eIFiso4G. The binding affinity of eIF4G, eIF4F, and eIFiso4G to S1-3 was reduced by 3-5-fold, consistent with the reduction in the ability of this mutant to promote cap-independent translation. Temperature-dependent binding studies revealed that binding of the TEV 5'-leader to these initiation factors has a large entropic contribution. Overall, these results demonstrate the first direct interaction of eIF4G with the TEV 5'-leader in the absence of other initiation factors. These data correlate well with the observed translational data and provide more detailed information on the translational strategy of potyviruses.
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Affiliation(s)
- Sibnath Ray
- Department of Chemistry, Hunter College and the Graduate Center, City University of New York, New York, New York 10021, USA
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28
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Bellsolell L, Cho-Park PF, Poulin F, Sonenberg N, Burley SK. Two structurally atypical HEAT domains in the C-terminal portion of human eIF4G support binding to eIF4A and Mnk1. Structure 2006; 14:913-23. [PMID: 16698552 DOI: 10.1016/j.str.2006.03.012] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2005] [Revised: 03/20/2006] [Accepted: 03/21/2006] [Indexed: 10/24/2022]
Abstract
The X-ray structure of the C-terminal region of human eukaryotic translation initiation factor 4G (eIF4G) has been determined at 2.2 A resolution, revealing two atypical HEAT-repeat domains. eIF4G recruits various translation factors and the 40S ribosomal subunit to the mRNA 5' end. In higher eukaryotes, the C terminus of eIF4G (4G/C) supports translational regulation by recruiting eIF4A, an RNA helicase, and Mnk1, the kinase responsible for phosphorylating eIF4E. Structure-guided surface mutagenesis and protein-protein interaction assays were used to identify binding sites for eIF4A and Mnk1 within the HEAT-repeats of 4G/C. p97/DAP5, a translational modulator homologous to eIF4G, lacks an eIF4A binding site in the corresponding region. The second atypical HEAT domain of the 4G/C binds Mnk1 using two conserved aromatic/acidic-box (AA-box) motifs. Within the first AA-box, the aromatic residues contribute to the hydrophobic core of the domain, while the acidic residues form a negatively charged surface feature suitable for electrostatic interactions with basic residues in Mnk1.
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Affiliation(s)
- Lluís Bellsolell
- Laboratories of Molecular Biophysics, The Rockefeller University, New York, New York 10021, USA
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29
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Abstract
The eukaryotic translation initiation factor (eIF) 4B promotes the RNA-dependent ATP hydrolysis activity and ATP-dependent RNA helicase activity of eIF4A and eIF4F during translation initiation. Although this function is conserved among plants, animals, and yeast, eIF4B is one of the least conserved of initiation factors at the sequence level. To gain insight into its functional conservation, the organization of the functional domains of eIF4B from wheat has been investigated. Plant eIF4B contains three RNA binding domains, one more than reported for mammalian or yeast eIF4B, and each domain exhibits a preference for purine-rich RNA. In addition to a conserved RNA recognition motif and a C-terminal RNA binding domain, wheat eIF4B contains a novel N-terminal RNA binding domain that requires a short, lysine-rich containing sequence. Both the lysine-rich motif and an adjacent, C-proximal motif are conserved with an N-proximal sequence in human and yeast eIF4B. The C-proximal motif within the N-terminal RNA binding domain in wheat eIF4B is required for interaction with eIFiso4G, an interaction not reported for other eIF4B proteins. Moreover, each RNA binding domain requires dimerization for binding activity. Two binding sites for the poly(A)-binding protein were mapped to a region within each of two conserved 41-amino acid repeat domains on either side of the C-terminal RNA binding domain. eIF4A bound to an adjacent region within each repeat, supporting a central role for these conserved eIF4B domains in facilitating interaction with other components of the translational machinery. These results support the notion that eIF4B functions by organizing multiple components of the translation initiation machinery and RNA.
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Affiliation(s)
- Shijun Cheng
- Department of Biochemistry, University of California, Riverside, California 92521-0129, USA
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30
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LeFebvre AK, Korneeva NL, Trutschl M, Cvek U, Duzan RD, Bradley CA, Hershey JWB, Rhoads RE. Translation initiation factor eIF4G-1 binds to eIF3 through the eIF3e subunit. J Biol Chem 2006; 281:22917-32. [PMID: 16766523 PMCID: PMC1880881 DOI: 10.1074/jbc.m605418200] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
eIF3 in mammals is the largest translation initiation factor ( approximately 800 kDa) and is composed of 13 nonidentical subunits designated eIF3a-m. The role of mammalian eIF3 in assembly of the 48 S complex occurs through high affinity binding to eIF4G. Interactions of eIF4G with eIF4E, eIF4A, eIF3, poly(A)-binding protein, and Mnk1/2 have been mapped to discrete domains on eIF4G, and conversely, the eIF4G-binding sites on all but one of these ligands have been determined. The only eIF4G ligand for which this has not been determined is eIF3. In this study, we have sought to identify the mammalian eIF3 subunit(s) that directly interact(s) with eIF4G. Established procedures for detecting protein-protein interactions gave ambiguous results. However, binding of partially proteolyzed HeLa eIF3 to the eIF3-binding domain of human eIF4G-1, followed by high throughput analysis of mass spectrometric data with a novel peptide matching algorithm, identified a single subunit, eIF3e (p48/Int-6). In addition, recombinant FLAG-eIF3e specifically competed with HeLa eIF3 for binding to eIF4G in vitro. Adding FLAG-eIF3e to a cell-free translation system (i) inhibited protein synthesis, (ii) caused a shift of mRNA from heavy to light polysomes, (iii) inhibited cap-dependent translation more severely than translation dependent on the HCV or CSFV internal ribosome entry sites, which do not require eIF4G, and (iv) caused a dramatic loss of eIF4G and eIF2alpha from complexes sedimenting at approximately 40 S. These data suggest a specific, direct, and functional interaction of eIF3e with eIF4G during the process of cap-dependent translation initiation, although they do not rule out participation of other eIF3 subunits.
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Affiliation(s)
- Aaron K. LeFebvre
- Department of Biochemistry and Molecular Biology and Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130
| | - Nadejda L. Korneeva
- Department of Biochemistry and Molecular Biology and Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130
| | - Marjan Trutschl
- Department of Computer Science, Louisiana State University, Shreveport, Louisiana 71115
| | - Urska Cvek
- Department of Computer Science, Louisiana State University, Shreveport, Louisiana 71115
| | - Roy D. Duzan
- Research Core Facility, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130
| | - Christopher A. Bradley
- Department of Biochemistry and Molecular Medicine, University of California, Davis, California 95616
| | - John W. B. Hershey
- Department of Biochemistry and Molecular Medicine, University of California, Davis, California 95616
| | - Robert E. Rhoads
- Department of Biochemistry and Molecular Biology and Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130
- To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1501 Kings Hwy., Shreveport, LA 71130-3932. Tel.: 318-675-5161; Fax: 318-675-5180; E-mail:
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31
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32
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Wei Z, Xue Y, Xu H, Gong W. Crystal structure of the C-terminal domain of S.cerevisiae eIF5. J Mol Biol 2006; 359:1-9. [PMID: 16616930 DOI: 10.1016/j.jmb.2006.03.037] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Revised: 03/08/2006] [Accepted: 03/15/2006] [Indexed: 11/19/2022]
Abstract
eIF5, a GTPase-activating protein (GAP) specific for eIF2, plays a critical role in pre-initiation complex assembly and correct AUG selection during eukaryotic translation initiation. eIF5 is involved in the formation of the multifactor complex (MFC), an important intermediate of the 43S pre-initiation complex. The C-terminal domain (CTD) of eIF5 functions as the structural core in the MFC assembly. Here we report the 1.5A crystal structure of eIF5-CTD, confirming that eIF5-CTD contains an atypical HEAT motif. In addition, analyzing the electrostatic potential and the distribution of conserved residues on the protein surface, we confirm and suggest some potential regions of interactions between eIF5-CTD and other eIFs. The structure of eIF5-CTD provides useful information in understanding the mechanism of the MFC assembly.
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Affiliation(s)
- Zhiyi Wei
- National Laboratory of Biomacromolecules, USTC-IBP Joint Laboratory for Protein Sciences, Institute of Biophysics, Chinese Academy of Sciences, Beijing, People's Republic of China
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33
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von der Haar T, Oku Y, Ptushkina M, Moerke N, Wagner G, Gross JD, McCarthy JEG. Folding transitions during assembly of the eukaryotic mRNA cap-binding complex. J Mol Biol 2005; 356:982-92. [PMID: 16405910 DOI: 10.1016/j.jmb.2005.12.034] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2005] [Revised: 12/09/2005] [Accepted: 12/10/2005] [Indexed: 10/25/2022]
Abstract
The cap-binding protein eIF4E is the first in a chain of translation initiation factors that recruit 40S ribosomal subunits to the 5' end of eukaryotic mRNA. During cap-dependent translation, this protein binds to the 5'-terminal m(7)Gppp cap of the mRNA, as well as to the adaptor protein eIF4G. The latter then interacts with small ribosomal subunit-bound proteins, thereby promoting the mRNA recruitment process. Here, we show apo-eIF4E to be a protein that contains extensive unstructured regions, which are induced to fold upon recognition of the cap structure. Binding of eIF4G to apo-eIF4E likewise induces folding of the protein into a state that is similar to, but not identical with, that of cap-bound eIF4E. At the same time, binding of each of the binding partners of eIF4E modulates the kinetics with which it interacts with the other partner. We present structural, kinetic and mutagenesis data that allow us to deduce some of the detailed folding transitions that take place during the eIF4E interactions.
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Affiliation(s)
- Tobias von der Haar
- Manchester Interdisciplinary Biocentre, c/o Jackson's Mill, University of Manchester, P.O. Box 88, Manchester M60 1QD, UK.
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34
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Yamamoto Y, Singh CR, Marintchev A, Hall NS, Hannig EM, Wagner G, Asano K. The eukaryotic initiation factor (eIF) 5 HEAT domain mediates multifactor assembly and scanning with distinct interfaces to eIF1, eIF2, eIF3, and eIF4G. Proc Natl Acad Sci U S A 2005; 102:16164-9. [PMID: 16254050 PMCID: PMC1283452 DOI: 10.1073/pnas.0507960102] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Indexed: 11/18/2022] Open
Abstract
Eukaryotic translation initiation factor (eIF) 5 is crucial for the assembly of the eukaryotic preinitiation complex. This activity is mediated by the ability of its C-terminal HEAT domain to interact with eIF1, eIF2, and eIF3 in the multifactor complex and with eIF4G in the 48S complex. However, the binding sites for these factors on eIF5-C-terminal domain (CTD) have not been known. Here we present a homology model for eIF5-CTD based on the HEAT domain of eIF2Bepsilon. We show that the binding site for eIF2beta is located in a surface area containing aromatic and acidic residues (aromatic/acidic boxes), that the binding sites for eIF1 and eIF3c are located in a conserved surface region of basic residues, and that eIF4G binds eIF5-CTD at an interface overlapping with the acidic area. Mutations in these distinct eIF5 surface areas impair GCN4 translational control by disrupting preinitiation complex interactions. These results indicate that the eIF5 HEAT domain is a critical nucleation core for preinitiation complex assembly and function.
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Affiliation(s)
- Yasufumi Yamamoto
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
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35
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Abstract
The eukaryotic translation initiation factors 4A (eIF4A) and 4G (eIF4G) are crucial for the assembly of the translationally active ribosome. Together with eIF4E, they form the eIF4F complex, which recruits the 40S subunit to the 5' cap of mRNA. The two-domain RNA helicase eIF4A is a very weak helicase by itself, but the activity is enhanced upon interaction with the scaffolding protein eIF4G. Here we show that, albeit both eIF4A domains play a role in binding the middle domain of eIF4G (eIF4G-m, amino acids 745-1003), the main interaction surface is located on the C-terminal domain. We use NMR spectroscopy to define the binding site and find that the contact surface is adjacent to the RNA-, ATP-, and eIF4A-NTD-interacting regions. Mutations of interface residues abrogated binding, confirmed the interface, and showed that the N-terminal end of eIF4G-m interacts with the C-terminal domain of eIF4A. The data suggest that eIF4G-m forms a soft clamp to stabilize the closed interdomain orientation of eIF4A. This model can explain the cooperativity between all binding partners of eIF4A (eIF4G, RNA, ATP) and stimulation of eIF4A activity in the eIF4F complex.
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Affiliation(s)
- Monika Oberer
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
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36
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Marintchev A, Wagner G. eIF4G and CBP80 Share a Common Origin and Similar Domain Organization: Implications for the Structure and Function of eIF4G†. Biochemistry 2005; 44:12265-72. [PMID: 16156639 DOI: 10.1021/bi051271v] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Eukaryotic translation initiation factor 4G (eIF4G) plays a critical role in protein expression, and is at the center of a complex regulatory network. Together with the cap-binding protein eIF4E, it recruits the small ribosomal subunit to the 5'-end of mRNA and promotes the assembly of a functional translation initiation complex, which scans along the mRNA to the translation start codon. Human eIF4G contains three consecutive HEAT domains, as well as long unstructured regions involved in multiple protein-protein interactions. Despite the accumulating data about the structure and function of eIF4G, the mechanisms of coordination and regulation of its interactions with other factors have remained largely unknown. Here, we present evidence that eIF4G and the large subunit of the nuclear cap-binding complex, CBP80, share a common origin and domain structure. We propose that the organization of the individual domains in eIF4G and CBP80 could also be conserved. The structure of CBP80, in complex with the nuclear cap-binding protein CBP20, is used to build a model for the mutual orientation of the domains in eIF4G and their interactions with other factors. The organization of the CBP80-CBP20 complex suggests how the activity of eIF4G in translation initiation could be regulated through a dynamic network of overlapping intra- and intermolecular interactions centered around the eIF4G HEAT domains.
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Affiliation(s)
- Assen Marintchev
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
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Takahashi K, Maruyama M, Tokuzawa Y, Murakami M, Oda Y, Yoshikane N, Makabe KW, Ichisaka T, Yamanaka S. Evolutionarily conserved non-AUG translation initiation in NAT1/p97/DAP5 (EIF4G2). Genomics 2005; 85:360-71. [PMID: 15718103 DOI: 10.1016/j.ygeno.2004.11.012] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Accepted: 11/22/2004] [Indexed: 11/17/2022]
Abstract
Only a few cases of exclusive translation initiation at non-AUG codons have been reported. We recently demonstrated that mammalian NAT1 mRNA, encoded by EIF4G2, uses GUG as its only translation initiation codon. In this study, we identified NAT1 orthologs from chicken, Xenopus, and zebrafish and found that in all species, the GUG codon also serves as the initiation codon. In all species, the GUG codon fulfilled the reported requirements for non-AUG initiation: an optimal Kozak motif and a downstream hairpin structure. Site-directed mutagenesis showed that nucleotides at positions -3 and +4 are critical for the GUG-mediated translation initiation in vitro. We found that NAT1 orthologs in Drosophila melanogaster and Halocynthia roretzi also use non-AUG start codons, demonstrating evolutionary conservation of the noncanonical translation initiation.
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Affiliation(s)
- Kazutoshi Takahashi
- Research and Education Center for Genetic Information, Nara Institute of Science and Technology, Ikoma 8916-5, Nara 630-0101, Japan
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38
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Byrd MP, Zamora M, Lloyd RE. Translation of eukaryotic translation initiation factor 4GI (eIF4GI) proceeds from multiple mRNAs containing a novel cap-dependent internal ribosome entry site (IRES) that is active during poliovirus infection. J Biol Chem 2005; 280:18610-22. [PMID: 15755734 DOI: 10.1074/jbc.m414014200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic translation initiation factor 4GI (eIF4GI) is an essential scaffolding protein required to recruit the 43 S complex to the 5'-end of mRNA during translation initiation. We have previously demonstrated that eIF4GI protein expression is translationally regulated. This regulation is mediated by cis-acting RNA elements, including an upstream open reading frame and an IRES that directs synthesis of five eIF4GI protein isoforms via alternative AUG initiation codon selection. Here, we further characterize eIF4GI IRES function and show that eIF4GI is expressed from several distinct mRNAs that vary via alternate promoter use and alternate splicing. Several mRNA variants contain the IRES element. We found that IRES activity mapped to multiple regions within the eIF4GI RNA sequence, but not within the 5'-UTR per se. However, the 5'-UTR enhanced IRES activity in vivo and played a role in initiation codon selection. The eIF4GI IRES was active when transfected into cells in an RNA form, and thus, does not require nuclear processing events for its function. However, IRES activity was found to be dependent upon the presence, in cis, of a 5' m7guanosine-cap. Despite this requirement, the eIF4GI IRES was activated by 2A protease cleavage of eIF4GI, in vitro, and retained the ability to promote translation during poliovirus-mediated inhibition of cap-dependent translation. These data indicate that intact eIF4GI protein is not required for the de novo synthesis of eIF4GI, suggesting its expression can continue under stress or infection conditions where eIF4GI is cleaved.
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Affiliation(s)
- Marshall P Byrd
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA
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Korneeva NL, First EA, Benoit CA, Rhoads RE. Interaction between the NH2-terminal domain of eIF4A and the central domain of eIF4G modulates RNA-stimulated ATPase activity. J Biol Chem 2004; 280:1872-81. [PMID: 15528191 DOI: 10.1074/jbc.m406168200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The eukaryotic translation factor 4A (eIF4A) is a member of DEA(D/H)-box RNA helicase family, a diverse group of proteins that couples ATP hydrolysis to RNA binding and duplex separation. eIF4A participates in the initiation of translation by unwinding secondary structure in the 5'-untranslated region of mRNAs and facilitating scanning by the 40 S ribosomal subunit for the initiation codon. eIF4A alone has only weak ATPase and helicase activities, but these are stimulated by eIF4G, eIF4B, and eIF4H. eIF4G has two eIF4A-binding sites, one in the central domain (cp(C3)) and one in the COOH-terminal domain (cp(C2)). In the current work, we demonstrate that these two eIF4G domains have different effects on the RNA-stimulated ATPase activity of eIF4A. cp(C3) stimulates ATP-hydrolytic efficiency by about 40-fold through two mechanisms: lowering K(m)(RNA) by 10-fold and raising k(cat) by 4-fold. cp(C3) also stimulates RNA cross-linking to eIF4A in an ATP-independent manner. Studies with eIF4G and eIF4A variants suggest a model by which cp(C3) alters the conformation of the catalytic site to favor RNA binding. cp(C2) does not stimulate ATPase activity and furthermore increases both K(m)(ATP) (at saturating RNA concentrations) and K(m)(RNA) (at subsaturating ATP concentrations). Both cp(C3) and cp(C2) directly interact with the NH(2)-terminal domain of eIF4A, which possesses conserved ATP- and oligonucleotide-binding motifs, but not with the COOH-terminal domain.
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Affiliation(s)
- Nadia L Korneeva
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130-3932, USA
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Malnou CE, Werner A, Borman AM, Westhof E, Kean KM. Effects of Vaccine Strain Mutations in Domain V of the Internal Ribosome Entry Segment Compared in the Wild Type Poliovirus Type 1 Context. J Biol Chem 2004; 279:10261-9. [PMID: 14672927 DOI: 10.1074/jbc.m307806200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Initiation of poliovirus (PV) protein synthesis is governed by an internal ribosome entry segment structured into several domains including domain V, which is accepted to be important in PV neurovirulence because it harbors an attenuating mutation in each of the vaccine strains developed by A. Sabin. To better understand how these single point mutations exert their effects, we placed each of them into the same genomic context, that of PV type 1. Only the mutation equivalent to the Sabin type 3 strain mutation resulted in significantly reduced viral growth both in HeLa and neuroblastoma cells. This correlated with poor translation efficiency in vitro and could be explained by a structural perturbation of the domain V of the internal ribosome entry segment, as evidenced by RNA melting experiments. We demonstrated that reduced cell death observed during infection by this mutant is due to the absence of inhibition of host cell translation. We confirmed that this shut-off is correlated principally with cleavage of eIF4GII and not eIF4GI and that this cleavage is significantly impaired in the case of the defective mutant. These data support the previously reported conclusion that the 2A protease has markedly different affinities for the two eIF4G isoforms.
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Affiliation(s)
- Cécile E Malnou
- Unité de Régulation de la Traduction Eucaryote et Virale, Institut Pasteur, 75724 Paris, France
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Miura T, Shiratori Y, Shimma N. Backbone resonance assignment of human eukaryotic translation initiation factor 4E (eIF4E) in complex with 7-methylguanosine diphosphate (m7GDP) and a 17-amino acid peptide derived from human eIF4GII. J Biomol NMR 2003; 27:279-280. [PMID: 12975586 DOI: 10.1023/a:1025442322316] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
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Abstract
The 2A proteinase (2Apro) of human rhinovirus 2 is a cysteine proteinase with a unique chymotrypsin-like fold. During viral replication, 2Apro performs self-processing by cleaving between its own N terminus and the C terminus of the preceding protein, VP1. Subsequently, 2Apro cleaves the two isoforms of the cellular protein, eukaryotic initiation factor (eIF) 4G. We have previously shown that HRV2 2Apro can directly bind to eIF4G isoforms. Here we demonstrate using deletion mutants of eIF4GI that HRV2 2Apro requires eIF4GI amino acids 600-674 for binding; however, the amino acids at the cleavage site, Arg681 downward arrow Gly, are not required. The HRV2 2Apro binding domain for eIF4GI was identified by site-directed mutagenesis. Specifically, mutations Leu17 --> Arg and Asp35 --> Glu severely impaired HRV2 2Apro binding and thus processing of eIF4GI in rabbit reticulocyte lysates; self-processing, however, was not affected. Alanine scanning analysis further identified the loop containing residues Tyr32, Ser33, and Ser34 as important for eIF4GI binding. Although Asp35 is part of the catalytic triad, most of the eIF4GI binding domain lies in a unique exosite structure absent from other chymotrypsin-like enzymes and is distinct from the substrate binding cleft. The exosite represents a novel virulence determinant that may allow the development of specific inhibitors for HRV2 2Apro.
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Affiliation(s)
- Nicole Foeger
- Max F. Perutz Laboratories, and Department of Medical Biochemistry, Division of Biochemistry, University of Vienna, Vienna Biocenter, Dr. Bohr-Gasse 9/3, A-1030 Vienna, Austria
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Scheper GC, Parra JL, Wilson M, Van Kollenburg B, Vertegaal ACO, Han ZG, Proud CG. The N and C termini of the splice variants of the human mitogen-activated protein kinase-interacting kinase Mnk2 determine activity and localization. Mol Cell Biol 2003; 23:5692-705. [PMID: 12897141 PMCID: PMC166352 DOI: 10.1128/mcb.23.16.5692-5705.2003] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2002] [Revised: 03/06/2003] [Accepted: 05/07/2003] [Indexed: 11/20/2022] Open
Abstract
The cap-binding eukaryotic initiation factor eIF4E is phosphorylated by the mitogen-activated protein (MAP) kinase-interacting kinases (Mnk's). Three forms of the Mnk's exist in human cells: Mnk1, Mnk2a, and Mnk2b. These last two are derived from the same gene by alternative splicing and differ only at their C termini. While Mnk2a contains a MAP kinase-binding site in this region, Mnk2b lacks such a sequence and is much less readily activated by MAP kinases in vitro. Expression of Mnk2b in mammalian cells leads to increased phosphorylation of eIF4E, showing that it acts as an eIF4E kinase in vivo. While Mnk2a is cytoplasmic, a substantial amount of Mnk2b is found in the nucleus. Both enzymes contain a stretch of basic residues in their N termini that plays a role in binding to eIF4G and functions as a nuclear localization signal. Binding of eIF4G or nuclear import appears to be regulated by the C terminus of Mnk2a. Furthermore, the MAP kinase-binding site of Mnk2a regulates nuclear entry. Within the nucleus, Mnk2b and certain variants of Mnk2a that are present in the nucleus colocalize with the promyelocytic leukemia protein PML, which also binds to eIF4E.
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Affiliation(s)
- Gert C Scheper
- Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dundee, United Kingdom
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44
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He H, von der Haar T, Singh CR, Ii M, Li B, Hinnebusch AG, McCarthy JEG, Asano K. The yeast eukaryotic initiation factor 4G (eIF4G) HEAT domain interacts with eIF1 and eIF5 and is involved in stringent AUG selection. Mol Cell Biol 2003; 23:5431-45. [PMID: 12861028 PMCID: PMC165723 DOI: 10.1128/mcb.23.15.5431-5445.2003] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Eukaryotic initiation factor 4G (eIF4G) promotes mRNA recruitment to the ribosome by binding to the mRNA cap- and poly(A) tail-binding proteins eIF4E and Pap1p. eIF4G also binds eIF4A at a distinct HEAT domain composed of five stacks of antiparallel alpha-helices. The role of eIF4G in the later steps of initiation, such as scanning and AUG recognition, has not been defined. Here we show that the entire HEAT domain and flanking residues of Saccharomyces cerevisiae eIF4G2 are required for the optimal interaction with the AUG recognition factors eIF5 and eIF1. eIF1 binds simultaneously to eIF4G and eIF3c in vitro, as shown previously for the C-terminal domain of eIF5. In vivo, co-overexpression of eIF1 or eIF5 reverses the genetic suppression of an eIF4G HEAT domain Ts(-) mutation by eIF4A overexpression. In addition, excess eIF1 inhibits growth of a second eIF4G mutant defective in eIF4E binding, which was also reversed by co-overexpression of eIF4A. Interestingly, excess eIF1 carrying the sui1-1 mutation, known to relax the accuracy of start site selection, did not inhibit the growth of the eIF4G mutant, and sui1-1 reduced the interaction between eIF4G and eIF1 in vitro. Moreover, a HEAT domain mutation altering eIF4G moderately enhances translation from a non-AUG codon. These results strongly suggest that the binding of the eIF4G HEAT domain to eIF1 and eIF5 is important for maintaining the integrity of the scanning ribosomal preinitiation complex.
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Affiliation(s)
- Hui He
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
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Hashemzadeh-Bonehi L, Curtis PS, Morley SJ, Thorpe JR, Pain VM. Overproduction of a conserved domain of fission yeast and mammalian translation initiation factor eIF4G causes aberrant cell morphology and results in disruption of the localization of F-actin and the organization of microtubules. Genes Cells 2003; 8:163-78. [PMID: 12581158 DOI: 10.1046/j.1365-2443.2003.00623.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
BACKGROUND The recruitment of mRNA for translation involves the assembly at the 5'cap of a complex of three initiation factors: the cap binding protein eIF4E, the ATP-dependent RNA helicase eIF4A and the scaffold protein eIF4G. eIF4G mediates the binding of this mRNA-protein complex to the 43S ribosomal preinitiation complex. There is growing recognition that the components of the translational apparatus interact functionally with cytoskeletal components. Here we report specific effects of the over-expression of human and fission yeast eIF4G domains on cell morphology in Schizosaccharomyces pombe. RESULTS A single gene encoding fission yeast eIF4G was identified and demonstrated to be essential. We have over-expressed fragments corresponding to the conserved functional domains of eIF4G. At expression levels that did not disrupt rates of overall translation or protein accumulation, a fragment of S. pombe eIF4G, 4G-NOB, corresponding to the minimal region of human eIF4G required to support cap-independent mRNA recruitment, was found to impair cell proliferation in fission yeast. This resulted from defects in cytokinesis, and was associated with the disruption of both microtubules and actin microfilaments. The over-expressed fragment was itself localized to the cell ends, the nuclear periphery and the septum. CONCLUSIONS This is the first demonstration of a link between a translation initiation factor and mechanisms controlling cell morphology. The data suggest a direct or indirect interaction between the functional domains of eIF4G and cellular structures involved in cytokinesis.
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Affiliation(s)
- Lida Hashemzadeh-Bonehi
- Biochemistry Laboratory, School of Biological Sciences, University of Sussex, Brighton BN1 9QG, UK
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Abstract
We have recently reported that HIV-1 protease (PR) cleaves the initiation factor of translation eIF4GI [Ventoso et al., Proc. Natl. Acad. Sci. USA 98 (2001) 12966-12971]. Here, we analyze the proteolytic activity of HIV-1 PR on eIF4GI and eIF4GII and its implications for the translation of mRNAs. HIV-1 PR efficiently cleaves eIF4GI, but not eIF4GII, in cell-free systems as well as in transfected mammalian cells. This specific proteolytic activity of the retroviral protease on eIF4GI was more selective than that observed with poliovirus 2A(pro). Despite the presence of an intact endogenous eIF4GII, cleavage of eIF4GI by HIV-1 PR was sufficient to impair drastically the translation of capped and uncapped mRNAs. In contrast, poliovirus IRES-driven translation was unaffected or even enhanced by HIV-1 PR after cleavage of eIF4GI. Further support for these in vitro results has been provided by the expression of HIV-1 PR in COS cells from a Gag-PR precursor. Our present findings suggest that eIF4GI intactness is necessary to maintain cap-dependent translation, not only in cell-free systems but also in mammalian cells.
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Affiliation(s)
- Celia Perales
- Centro de Biologi;a Molecular 'Severo Ochoa', Facultad de Ciencias, Universidad Autónoma-CSIC, Cantoblanco 28049, Madrid, Spain
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Abstract
The leader proteinase (L(pro)) of foot and mouth disease virus is a papain-like cysteine proteinase. After processing itself from the polyprotein, L(pro) then cleaves the host protein eukaryotic initiation factor (eIf) 4GI, thus preventing protein synthesis from capped mRNA in the infected cell. We have investigated L(pro) interaction with eIF4GI and its isoform, eIF4GII. L(pro), expressed as a catalytically inactive fusion protein with glutathione S-transferase, binds specifically to eIF4G isomers in rabbit reticulocyte lysates. Deletion and specific mutagenesis were used to map the binding domain on L(pro) to residues 183-195 of the C-terminal extension and to residue Cys(133). These residues of the C-terminal extension and Cys(133) are adjacent in the crystal structure but lie about 25 A from the active site. The region on eIF4GI recognized by the L(pro) C-terminal extension was mapped to residues 640-669 using eIF4GI fragments generated by proteolysis or by in vitro translation. The L(pro) cleavage site at Gly(674) downward arrow Arg(675) was not necessary for binding. Similar experiments with human rhinovirus 2A proteinase (2A(pro)), a chymotrypsin-like cysteine proteinase that also cleaves eIF4G isoforms, revealed that 2A(pro) can also bind to eIF4GI fragments lacking its cleavage site. These experiments strongly suggest a novel interaction between picornaviral proteinases and eIF4G isoforms.
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Affiliation(s)
- Nicole Foeger
- Institute of Medical Biochemistry, Division of Biochemistry, University of Vienna, Vienna Bio Center, Dr. Bohr-Gasse 9/3, Austria
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Borman AM, Michel YM, Malnou CE, Kean KM. Free poly(A) stimulates capped mRNA translation in vitro through the eIF4G-poly(A)-binding protein interaction. J Biol Chem 2002; 277:36818-24. [PMID: 12138105 DOI: 10.1074/jbc.m205065200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 5' cap and 3' poly(A) tail of classical eukaryotic mRNAs functionally communicate to synergistically enhance translation initiation. Synergy has been proposed to result in part from facilitated ribosome recapture on circularized mRNAs. Here, we demonstrate that this is not the case. In poly(A)-dependent, ribosome-depleted rabbit reticulocyte lysates, the addition of exogenous poly(A) chains of physiological length dramatically stimulated translation of a capped, nonpolyadenylated mRNA. When the poly(A):RNA ratio approached 1, exogenous poly(A) stimulated translation to the same extent as the presence of a poly(A) tail at the mRNA 3' end. In addition, exogenous poly(A) significantly improved translation of capped mRNAs carrying short poly(A(50)) tails. Trans stimulation of translation by poly(A) required the eIF4G-poly(A)-binding protein interaction and resulted in increased affinity of eIF4E for the mRNA cap, exactly as we recently described for cap-poly(A) synergy. These results formally demonstrate that mRNA circularization per se is not the cause of cap-poly(A) synergy at least in vitro.
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Affiliation(s)
- Andrew M Borman
- Unité Postulante de Régulation de la Traduction Eucaryote et Virale, CNRS URA 1966, Institut Pasteur, Paris, France
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