1
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Gayen A, Alone P. eIF2β zinc-binding domain interacts with the eIF2γ subunit through the guanine nucleotide binding interface to promote Met-tRNAiMet binding. Biosci Rep 2024; 44:BSR20240438. [PMID: 38873976 PMCID: PMC11230868 DOI: 10.1042/bsr20240438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2024] [Revised: 06/09/2024] [Accepted: 06/13/2024] [Indexed: 06/15/2024] Open
Abstract
The heterotrimeric eIF2 complex consists of a core eIF2γ subunit to which binds eIF2α and eIF2β subunits and plays an important role in delivering the Met-tRNAiMet to the 40S ribosome and start codon selection. The intricacies of eIF2β-γ interaction in promoting Met-tRNAiMet binding are not clearly understood. Previously, the zinc-binding domain (ZBD) eIF2βS264Y mutation was reported to cause Met-tRNAiMet binding defect due to the intrinsic GTPase activity. We showed that the eIF2βS264Y mutation has eIF2β-γ interaction defect. Consistently, the eIF2βT238A intragenic suppressor mutation restored the eIF2β-γ and Met-tRNAiMet binding. The eIF2β-ZBD residues Asn252Asp and Arg253Ala mutation caused Met-tRNAiMet binding defect that was partially rescued by the eIF2βT238A mutation, suggesting the eIF2β-ZBD modulates Met-tRNAiMet binding. The suppressor mutation rescued the translation initiation fidelity defect of the eIF2γN135D SW-I mutation and eIF2βF217A/Q221A double mutation in the HTH domain. The eIF2βT238A suppressor mutation could not rescue the eIF2β binding defect of the eIF2γV281K mutation; however, combining the eIF2βS264Y mutation with the eIF2γV281K mutation was lethal. In addition to the previously known interaction of eIF2β with the eIF2γ subunit via its α1-helix, the eIF2β-ZBD also interacts with the eIF2γ subunit via guanine nucleotide-binding interface; thus, the eIF2β-γ interacts via two distinct binding sites.
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Affiliation(s)
- Aranyadip Gayen
- School of Biological Sciences, National Institute of Science Education and Research Bhubaneswar, P.O Jatni, Khurda 752050, India
- Homi Bhabha National Institute (HBNI), Anushakti Nagar, Mumbai 400094, India
| | - Pankaj V. Alone
- School of Biological Sciences, National Institute of Science Education and Research Bhubaneswar, P.O Jatni, Khurda 752050, India
- Homi Bhabha National Institute (HBNI), Anushakti Nagar, Mumbai 400094, India
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2
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Grosely R, Alvarado C, Ivanov IP, Nicholson OB, Puglisi JD, Dever TE, Lapointe CP. eIF1 and eIF5 dynamically control translation start site fidelity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.10.602410. [PMID: 39026837 PMCID: PMC11257575 DOI: 10.1101/2024.07.10.602410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2024]
Abstract
Translation initiation defines the identity of a synthesized protein through selection of a translation start site on a messenger RNA. This process is essential to well-controlled protein synthesis, modulated by stress responses, and dysregulated in many human diseases. The eukaryotic initiation factors eIF1 and eIF5 interact with the initiator methionyl-tRNAi Met on the 40S ribosomal subunit to coordinate start site selection. Here, using single-molecule analysis of in vitro reconstituted human initiation combined with translation assays in cells, we examine eIF1 and eIF5 function. During translation initiation on a panel of RNAs, we monitored both proteins directly and in real time using single-molecule fluorescence. As expected, eIF1 loaded onto mRNAs as a component of the 43S initiation complex. Rapid (~ 2 s) eIF1 departure required a translation start site and was delayed by alternative start sites and a longer 5' untranslated region (5'UTR). After its initial departure, eIF1 rapidly and transiently sampled initiation complexes, with more prolonged sampling events on alternative start sites. By contrast, eIF5 only transiently bound initiation complexes late in initiation immediately prior to association of eIF5B, which allowed joining of the 60S ribosomal subunit. eIF5 association required the presence of a translation start site and was inhibited and destabilized by alternative start sites. Using both knockdown and overexpression experiments in human cells, we validated that eIF1 and eIF5 have opposing roles during initiation. Collectively, our findings demonstrate how multiple eIF1 and eIF5 binding events control start-site selection fidelity throughout initiation, which is tuned in response to changes in the levels of both proteins.
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Affiliation(s)
- Rosslyn Grosely
- Dept. of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Carlos Alvarado
- Dept. of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Ivaylo P. Ivanov
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | | | - Joseph D. Puglisi
- Dept. of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Thomas E. Dever
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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3
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Brito Querido J, Díaz-López I, Ramakrishnan V. The molecular basis of translation initiation and its regulation in eukaryotes. Nat Rev Mol Cell Biol 2024; 25:168-186. [PMID: 38052923 DOI: 10.1038/s41580-023-00624-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/24/2023] [Indexed: 12/07/2023]
Abstract
The regulation of gene expression is fundamental for life. Whereas the role of transcriptional regulation of gene expression has been studied for several decades, it has been clear over the past two decades that post-transcriptional regulation of gene expression, of which translation regulation is a major part, can be equally important. Translation can be divided into four main stages: initiation, elongation, termination and ribosome recycling. Translation is controlled mainly during its initiation, a process which culminates in a ribosome positioned with an initiator tRNA over the start codon and, thus, ready to begin elongation of the protein chain. mRNA translation has emerged as a powerful tool for the development of innovative therapies, yet the detailed mechanisms underlying the complex process of initiation remain unclear. Recent studies in yeast and mammals have started to shed light on some previously unclear aspects of this process. In this Review, we discuss the current state of knowledge on eukaryotic translation initiation and its regulation in health and disease. Specifically, we focus on recent advances in understanding the processes involved in assembling the 43S pre-initiation complex and its recruitment by the cap-binding complex eukaryotic translation initiation factor 4F (eIF4F) at the 5' end of mRNA. In addition, we discuss recent insights into ribosome scanning along the 5' untranslated region of mRNA and selection of the start codon, which culminates in joining of the 60S large subunit and formation of the 80S initiation complex.
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Affiliation(s)
- Jailson Brito Querido
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI, USA
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
| | - Irene Díaz-López
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK
| | - V Ramakrishnan
- MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK.
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4
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Fang JC, Liu MJ. Translation initiation at AUG and non-AUG triplets in plants. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2023; 335:111822. [PMID: 37574140 DOI: 10.1016/j.plantsci.2023.111822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 07/22/2023] [Accepted: 08/07/2023] [Indexed: 08/15/2023]
Abstract
In plants and other eukaryotes, precise selection of translation initiation site (TIS) on mRNAs shapes the proteome in response to cellular events or environmental cues. The canonical translation of mRNAs initiates at a 5' proximal AUG codon in a favorable context. However, the coding and non-coding regions of plant genomes contain numerous unannotated alternative AUG and non-AUG TISs. Determining how and why these unexpected and prevalent TISs are activated in plants has emerged as an exciting research area. In this review, we focus on the selection of plant TISs and highlight studies that revealed previously unannotated TISs used in vivo via comparative genomics and genome-wide profiling of ribosome positioning and protein N-terminal ends. The biological signatures of non-AUG TIS-initiated open reading frames (ORFs) in plants are also discussed. We describe what is understood about cis-regulatory RNA elements and trans-acting eukaryotic initiation factors (eIFs) in the site selection for translation initiation by featuring the findings in plants along with supporting findings in non-plant species. The prevalent, unannotated TISs provide a hidden reservoir of ORFs that likely help reshape plant proteomes in response to developmental or environmental cues. These findings underscore the importance of understanding the mechanistic basis of TIS selection to functionally annotate plant genomes, especially for crops with large genomes.
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Affiliation(s)
- Jhen-Cheng Fang
- Biotechnology Center in Southern Taiwan, Academia Sinica, Tainan 711, Taiwan
| | - Ming-Jung Liu
- Biotechnology Center in Southern Taiwan, Academia Sinica, Tainan 711, Taiwan; Agricultural Biotechnology Research Center, Academia Sinica, Taipei 115, Taiwan.
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5
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Yang H, Chen T, Denoyelle S, Chen L, Fan J, Zhang Y, Halperin JA, Chorev M, Aktas BH. Role of symmetry in 3,3-diphenyl-1,3-dihydroindol-2-one derivatives as inhibitors of translation initiation. Bioorg Med Chem Lett 2023; 80:129119. [PMID: 36581302 PMCID: PMC9922553 DOI: 10.1016/j.bmcl.2022.129119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Revised: 12/13/2022] [Accepted: 12/23/2022] [Indexed: 12/28/2022]
Abstract
The ternary complex (eIF2·GTP·Met-tRNAiMet) and the eIF4F complex assembly are two major regulatory steps in the eukaryotic translation initiation. Inhibition of the ternary complex assembly is therefore a promising target for the development of novel anti-cancer therapeutics. Building on the finding that clotrimazole (CLT), a molecular probe that depletes intracellular Ca2+ stores and subsequently induce eIF2α phosphorylation, inhibit translation initiation, and reduce preferentially the expression of oncoproteins over "housekeeping" ones,1-3 we undertook structure activity relationship (SAR) studies that identified 3,3-diarylindoline-2-one #1181 as an interesting scaffold. Compound #1181 also induce phosphorylation of eIF2α thereby reducing the availability of the ternary complex, which leads to inhibition of translation initiation.4 Our subsequent efforts focused on understanding SAR iterative lead optimization to enhance potency and improve bioavailability. Herein, we report a complementing study focusing on heavily substituted symmetric and asymmetric 3,3-(o,m-disubstituted)diarylindoline-2-ones. These compounds were evaluated by the dual luciferase reporter ternary complex assay that recapitualates phosphorylation of eIF2α in a quantitative manner. We also evaluated all compounds by sulforhodamine B assay, which measures the overall effect of compounds on cell proliferations and/or viability.
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Affiliation(s)
- Hongwei Yang
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA.
| | - Ting Chen
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA
| | - Séverine Denoyelle
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA
| | - Limo Chen
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA
| | - Jing Fan
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA
| | - Yingzhen Zhang
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA
| | - José A Halperin
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA; Harvard Medical School, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA
| | - Michael Chorev
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA; Harvard Medical School, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA.
| | - Bertal H Aktas
- Brigham and Women's Hospital, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA; Harvard Medical School, Division of Hematology, 4 Balckfan Circle. HIM 7, Boston, MA 02115, USA.
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6
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Fujita Y, Kameda T, Singh CR, Pepper W, Cecil A, Hilgers M, Thornton M, Asano I, Moravek C, Togashi Y, Saito H, Asano K. Translational recoding by chemical modification of non-AUG start codon ribonucleotide bases. SCIENCE ADVANCES 2022; 8:eabm8501. [PMID: 35394828 DOI: 10.1126/sciadv.abm8501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
In contrast to prokaryotes wherein GUG and UUG are permissive start codons, initiation frequencies from non-AUG codons are generally low in eukaryotes, with CUG being considered as strongest. Here, we report that combined 5-cytosine methylation (5mC) and pseudouridylation (Ψ) of near-cognate non-AUG start codons convert GUG and UUG initiation strongly favored over CUG initiation in eukaryotic translation under a certain context. This prokaryotic-like preference is attributed to enhanced NUG initiation by Ψ in the second base and reduced CUG initiation by 5mC in the first base. Molecular dynamics simulation analysis of tRNAiMet anticodon base pairing to the modified codons demonstrates that Ψ universally raises the affinity of codon:anticodon pairing within the ribosomal preinitiation complex through partially mitigating discrimination against non-AUG codons imposed by eukaryotic initiation factor 1. We propose that translational control by chemical modifications of start codon bases can offer a new layer of proteome diversity regulation and therapeutic mRNA technology.
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Affiliation(s)
- Yoshihiko Fujita
- Center for iPS Cell Research and Application, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | - Takeru Kameda
- Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-0046, Japan
- RIKEN Center for Biosystems Dynamics Research (BDR), Wako, Saitama 351-0198, Japan
- College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
| | - Chingakham Ranjit Singh
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Whitney Pepper
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Ariana Cecil
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Madelyn Hilgers
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Mackenzie Thornton
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Izumi Asano
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Carter Moravek
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Yuichi Togashi
- College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
- Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8530, Japan
- Research Center for the Mathematics on Chromatin Live Dynamics (RcMcD), Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan 739-8530
- RIKEN Center for Biosystems Dynamics Research (BDR), Higashi-Hiroshima, Hiroshima 739-0046, Japan
| | - Hirohide Saito
- Center for iPS Cell Research and Application, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | - Katsura Asano
- Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
- Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8530, Japan
- Hiroshima Research Center for Healthy Aging, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8530, Japan
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7
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Ram AK, Mallik M, Reddy RR, Suryawanshi AR, Alone PV. Altered proteome in translation initiation fidelity defective eIF5 G31R mutant causes oxidative stress and DNA damage. Sci Rep 2022; 12:5033. [PMID: 35322093 PMCID: PMC8943034 DOI: 10.1038/s41598-022-08857-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Accepted: 03/07/2022] [Indexed: 12/15/2022] Open
Abstract
The recognition of the AUG start codon and selection of an open reading frame (ORF) is fundamental to protein biosynthesis. Defect in the fidelity of start codon selection adversely affect proteome and have a pleiotropic effect on cellular function. Using proteomic techniques, we identified differential protein abundance in the translation initiation fidelity defective eIF5G31R mutant that initiates translation using UUG codon in addition to the AUG start codon. Consistently, the eIF5G31R mutant altered proteome involved in protein catabolism, nucleotide biosynthesis, lipid biosynthesis, carbohydrate metabolism, oxidation–reduction pathway, autophagy and re-programs the cellular pathways. The utilization of the upstream UUG codons by the eIF5G31R mutation caused downregulation of uridylate kinase expression, sensitivity to hydroxyurea, and DNA damage. The eIF5G31R mutant cells showed lower glutathione levels, high ROS activity, and sensitivity to H2O2.
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Affiliation(s)
- Anup Kumar Ram
- School of Biological Sciences, National Institute of Science Education and Research Bhubaneswar, P.O Jatni, Khurda, 752050, India.,Homi Bhabha National Institute (HBNI), Anushakti Nagar, Mumbai, 400094, India
| | - Monalisha Mallik
- School of Biological Sciences, National Institute of Science Education and Research Bhubaneswar, P.O Jatni, Khurda, 752050, India.,Homi Bhabha National Institute (HBNI), Anushakti Nagar, Mumbai, 400094, India
| | - R Rajendra Reddy
- Clinical Proteomics, DBT-Institute of Life Sciences, Bhubaneswar, Odisha, 751023, India
| | | | - Pankaj V Alone
- School of Biological Sciences, National Institute of Science Education and Research Bhubaneswar, P.O Jatni, Khurda, 752050, India. .,Homi Bhabha National Institute (HBNI), Anushakti Nagar, Mumbai, 400094, India.
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8
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Llácer JL, Hussain T, Dong J, Villamayor L, Gordiyenko Y, Hinnebusch AG. Large-scale movement of eIF3 domains during translation initiation modulate start codon selection. Nucleic Acids Res 2021; 49:11491-11511. [PMID: 34648019 PMCID: PMC8599844 DOI: 10.1093/nar/gkab908] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 09/20/2021] [Accepted: 09/22/2021] [Indexed: 11/13/2022] Open
Abstract
The eukaryotic initiation factor 3 (eIF3) complex is involved in every step of translation initiation, but there is limited understanding of its molecular functions. Here, we present a single particle electron cryomicroscopy (cryo-EM) reconstruction of yeast 48S ribosomal preinitiation complex (PIC) in an open conformation conducive to scanning, with core subunit eIF3b bound on the 40S interface near the decoding center in contact with the ternary complex eIF2·GTP·initiator tRNA. eIF3b is relocated together with eIF3i from their solvent interface locations observed in other PIC structures, with eIF3i lacking 40S contacts. Re-processing of micrographs of our previous 48S PIC in a closed state also suggests relocation of the entire eIF3b-3i-3g-3a-Cter module during the course of initiation. Genetic analysis indicates that high fidelity initiation depends on eIF3b interactions at the 40S subunit interface that promote the closed PIC conformation, or facilitate the relocation of eIF3b/eIF3i to the solvent interface, on start codon selection.
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Affiliation(s)
- Jose L Llácer
- Instituto de Biomedicina de Valencia (IBV-CSIC), Valencia 46010, Spain.,Centro para Investigación Biomédica en Red sobre Enfermedades Raras CIBERER-ISCIII, Valencia, Spain
| | - Tanweer Hussain
- Molecular Reproduction, Development and Genetics (MRDG), Biological Sciences Building, Indian Institute of Science, Bangalore 560012, India
| | - Jinsheng Dong
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Laura Villamayor
- Instituto de Biomedicina de Valencia (IBV-CSIC), Valencia 46010, Spain
| | | | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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9
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Kratzat H, Mackens-Kiani T, Ameismeier M, Potocnjak M, Cheng J, Dacheux E, Namane A, Berninghausen O, Herzog F, Fromont-Racine M, Becker T, Beckmann R. A structural inventory of native ribosomal ABCE1-43S pre-initiation complexes. EMBO J 2020; 40:e105179. [PMID: 33289941 PMCID: PMC7780240 DOI: 10.15252/embj.2020105179] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 09/21/2020] [Accepted: 09/29/2020] [Indexed: 11/24/2022] Open
Abstract
In eukaryotic translation, termination and ribosome recycling phases are linked to subsequent initiation of a new round of translation by persistence of several factors at ribosomal sub‐complexes. These comprise/include the large eIF3 complex, eIF3j (Hcr1 in yeast) and the ATP‐binding cassette protein ABCE1 (Rli1 in yeast). The ATPase is mainly active as a recycling factor, but it can remain bound to the dissociated 40S subunit until formation of the next 43S pre‐initiation complexes. However, its functional role and native architectural context remains largely enigmatic. Here, we present an architectural inventory of native yeast and human ABCE1‐containing pre‐initiation complexes by cryo‐EM. We found that ABCE1 was mostly associated with early 43S, but also with later 48S phases of initiation. It adopted a novel hybrid conformation of its nucleotide‐binding domains, while interacting with the N‐terminus of eIF3j. Further, eIF3j occupied the mRNA entry channel via its ultimate C‐terminus providing a structural explanation for its antagonistic role with respect to mRNA binding. Overall, the native human samples provide a near‐complete molecular picture of the architecture and sophisticated interaction network of the 43S‐bound eIF3 complex and the eIF2 ternary complex containing the initiator tRNA.
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Affiliation(s)
- Hanna Kratzat
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | - Timur Mackens-Kiani
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | - Michael Ameismeier
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | - Mia Potocnjak
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | - Jingdong Cheng
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | - Estelle Dacheux
- Génétique des Interactions Macromoléculaires, UMR3525 CNRS, Institut Pasteur, Paris, France
| | - Abdelkader Namane
- Génétique des Interactions Macromoléculaires, UMR3525 CNRS, Institut Pasteur, Paris, France
| | - Otto Berninghausen
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | - Franz Herzog
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | | | - Thomas Becker
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
| | - Roland Beckmann
- Gene Center and Center for Integrated Protein Science Munich, Department of Biochemistry, University of Munich, Munich, Germany
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10
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Thakur A, Gaikwad S, Vijjamarri AK, Hinnebusch AG. eIF2α interactions with mRNA control accurate start codon selection by the translation preinitiation complex. Nucleic Acids Res 2020; 48:10280-10296. [PMID: 32955564 DOI: 10.1093/nar/gkaa761] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 08/26/2020] [Accepted: 09/02/2020] [Indexed: 11/13/2022] Open
Abstract
In translation initiation, AUG recognition triggers rearrangement of the 48S preinitiation complex (PIC) from an open conformation to a closed state with more tightly-bound Met-tRNAi. Cryo-EM structures have revealed interactions unique to the closed complex between arginines R55/R57 of eIF2α with mRNA, including the -3 nucleotide of the 'Kozak' context. We found that R55/R57 substitutions reduced recognition of a UUG start codon at HIS4 in Sui- cells (Ssu- phenotype); and in vitro, R55G-R57E accelerated dissociation of the eIF2·GTP·Met-tRNAi ternary complex (TC) from reconstituted PICs with a UUG start codon, indicating destabilization of the closed complex. R55/R57 substitutions also decreased usage of poor-context AUGs in SUI1 and GCN4 mRNAs in vivo. In contrast, eIF2α-R53 interacts with the rRNA backbone only in the open complex, and the R53E substitution enhanced initiation at a UUG codon (Sui- phenotype) and poor-context AUGs, while reducing the rate of TC loading (Gcd- phenotype) in vivo. Consistently, R53E slowed TC binding to the PIC while decreasing TC dissociation at UUG codons in vitro, indicating destabilization of the open complex. Thus, distinct interactions of eIF2α with rRNA or mRNA stabilize first the open, and then closed, conformation of the PIC to influence the accuracy of initiation in vivo.
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Affiliation(s)
- Anil Thakur
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA.,Regional Centre for Biotechnology, 3rd milestone Gurgaon-Faridabad Expressway, Faridabad 121001, India
| | - Swati Gaikwad
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA
| | - Anil K Vijjamarri
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA
| | - Alan G Hinnebusch
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA
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11
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Lomakin IB, De S, Wang J, Borkar AN, Steitz TA. Crystal structure of the C-terminal domain of DENR. Comput Struct Biotechnol J 2020; 18:696-704. [PMID: 32257053 PMCID: PMC7114459 DOI: 10.1016/j.csbj.2020.03.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 03/09/2020] [Accepted: 03/11/2020] [Indexed: 02/04/2023] Open
Abstract
The density regulated protein (DENR) forms a stable heterodimer with malignant T-cell-amplified sequence 1 (MCT-1). DENR-MCT-1 heterodimer then participates in regulation of non-canonical translation initiation and ribosomal recycling. The N-terminal domain of DENR interacts with MCT-1 and carries a classical tetrahedral zinc ion-binding site, which is crucial for the dimerization. DENR-MCT-1 binds the small (40S) ribosomal subunit through interactions between MCT-1 and helix h24 of the 18S rRNA, and through interactions between the C-terminal domain of DENR and helix h44 of the 18S rRNA. This later interaction occurs in the vicinity of the P site that is also the binding site for canonical translation initiation factor eIF1, which plays the key role in initiation codon selection and scanning. Sequence homology modeling and a low-resolution crystal structure of the DENR-MCT-1 complex with the human 40S subunit suggests that the C-terminal domain of DENR and eIF1 adopt a similar fold. Here we present the crystal structure of the C-terminal domain of DENR determined at 1.74 Å resolution, which confirms its resemblance to eIF1 and advances our understanding of the mechanism by which DENR-MCT-1 regulates non-canonical translation initiation and ribosomal recycling.
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Affiliation(s)
- Ivan B. Lomakin
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA
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12
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Thakur A, Marler L, Hinnebusch AG. A network of eIF2β interactions with eIF1 and Met-tRNAi promotes accurate start codon selection by the translation preinitiation complex. Nucleic Acids Res 2019; 47:2574-2593. [PMID: 30576497 PMCID: PMC6411837 DOI: 10.1093/nar/gky1274] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Revised: 12/07/2018] [Accepted: 12/15/2018] [Indexed: 11/14/2022] Open
Abstract
In translation initiation, a 43S preinitiation complex (PIC) containing eIF1 and a ternary complex (TC) of GTP-bound eIF2 and Met-RNAi scans the mRNA for the start codon. AUG recognition triggers eIF1 release and rearrangement from an open PIC conformation to a closed state with more tightly-bound Met-tRNAi (PIN state). Cryo-EM models reveal eIF2β contacts with eIF1 and Met-tRNAi exclusive to the open complex that should destabilize the closed state. eIF2β or eIF1 substitutions disrupting these contacts increase initiation at UUG codons, and compound substitutions also derepress translation of GCN4, indicating slower TC recruitment. The latter substitutions slow TC loading while stabilizing TC binding at UUG codons in reconstituted PICs, indicating a destabilized open complex and shift to the closed/PIN state. An eIF1 substitution that should strengthen the eIF2β:eIF1 interface has the opposite genetic and biochemical phenotypes. eIF2β is also predicted to restrict Met-tRNAi movement into the closed/PIN state, and substitutions that should diminish this clash increase UUG initiation in vivo and stabilize Met-tRNAi binding at UUG codons in vitro with little effect on TC loading. Thus, eIF2β anchors eIF1 and TC to the open complex, enhancing PIC assembly and scanning, while impeding rearrangement to the closed conformation at non-AUG codons.
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Affiliation(s)
- Anil Thakur
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA
| | - Laura Marler
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA
| | - Alan G Hinnebusch
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA
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13
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Young-Baird SK, Shin BS, Dever TE. MEHMO syndrome mutation EIF2S3-I259M impairs initiator Met-tRNAiMet binding to eukaryotic translation initiation factor eIF2. Nucleic Acids Res 2019; 47:855-867. [PMID: 30517694 PMCID: PMC6344876 DOI: 10.1093/nar/gky1213] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 11/26/2018] [Indexed: 01/20/2023] Open
Abstract
The heterotrimeric eukaryotic translation initiation factor (eIF) 2 plays critical roles in delivering initiator Met-tRNAiMet to the 40S ribosomal subunit and in selecting the translation initiation site. Genetic analyses of patients with MEHMO syndrome, an X-linked intellectual disability syndrome, have identified several unique mutations in the EIF2S3 gene that encodes the γ subunit of eIF2. To gain insights into the molecular consequences of MEHMO syndrome mutations on eIF2 function, we generated a yeast model of the human eIF2γ-I259M mutant, previously identified in a patient with MEHMO syndrome. The corresponding eIF2γ-I318M mutation impaired yeast cell growth and derepressed GCN4 expression, an indicator of defective eIF2–GTP–Met-tRNAiMet complex formation, and, likewise, overexpression of human eIF2γ-I259M derepressed ATF4 messenger RNA translation in human cells. The yeast eIF2γ-I318M mutation also increased initiation from near-cognate start codons. Biochemical analyses revealed a defect in Met-tRNAiMet binding to the mutant yeast eIF2 complexes in vivo and in vitro. Overexpression of tRNAiMet restored Met-tRNAiMet binding to eIF2 in vivo and rescued the growth defect in the eIF2γ-I318M strain. Based on these findings and the structure of eIF2, we propose that the I259M mutation impairs Met-tRNAiMet binding, causing altered control of protein synthesis that underlies MEHMO syndrome.
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Affiliation(s)
- Sara K Young-Baird
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.,National Institute of General Medical Sciences, National Institutes of Health, Bethesda, MD 20892, USA
| | - Byung-Sik Shin
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Thomas E Dever
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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14
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Antony A C, Ram AK, Dutta K, Alone PV. Ribosomal mutation in helix 32 of 18S rRNA alters fidelity of eukaryotic translation start site selection. FEBS Lett 2019; 593:852-867. [PMID: 30900251 DOI: 10.1002/1873-3468.13369] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 03/14/2019] [Accepted: 03/18/2019] [Indexed: 11/09/2022]
Abstract
The 40S ribosome plays a critical role in start codon selection. To gain insights into the role of its 18S rRNA in start codon selection, a suppressor screen was performed that suppressed the preferential UUG start codon recognition (Suppressor of initiation codon: Sui- phenotype) associated with the eIF5G31R mutant. The C1209U mutation in helix h32 of 18S rRNA was found to suppress the Sui- and Gcn- (failure to derepress GCN4 expression) phenotype of the eIF5G31R mutant. The C1209U mutation suppressed Sui- and Gcd- (constitutive derepression of GCN4 expression) phenotype of eIF2βS264Y , eIF1K60E , and eIF1A-ΔC mutation. We propose that the C1209U mutation in 40S ribosomal may perturb the premature head rotation in 'Closed/PIN ' state and enhance the stringency of translation start site selection.
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Affiliation(s)
- Charles Antony A
- School of Biological Sciences, National Institute of Science Education and Research, Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
| | - Anup Kumar Ram
- School of Biological Sciences, National Institute of Science Education and Research, Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
| | - Kalloly Dutta
- School of Biological Sciences, National Institute of Science Education and Research, Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
| | - Pankaj V Alone
- School of Biological Sciences, National Institute of Science Education and Research, Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
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15
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Fidelity of HIS4 start codon selection influences 3-amino-1,2,4-triazole sensitivity in GTPase activating protein function defective eIF5. J Genet 2018. [DOI: 10.1007/s12041-018-0989-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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16
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Charles Antony A, Alone PV. Fidelity of HIS4 start codon selection influences 3-amino-1,2,4-triazole sensitivity in GTPase activating protein function defective eIF5. J Genet 2018; 97:953-964. [PMID: 30262708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The eIF5 protein plays an important role in the fidelity of AUG start codon selection. However, the hyper GTPase eIF5G31R mutation in yeast causes preferential utilization of UUG as initiation codon and is termed as suppressor of initiation codon (Sui-) phenotype. The eIF5G31R mutant recognizes upUUG initiation codon from the 5' regulatory leader region of GCN4 transcript and dominantly represses GCN4 expression thereby conferring sensitivity to 3-amino-1,2,4-triazole (3AT)-induced starvation. The 3AT sensitivity was rescued by supplementing HIS4UUG allele. The eIF5G31R mutant has a better efficiency of UUG codon recognition from the HIS4UUG allele under starvation conditions. Moreover, the expression of HIS4UUG allele was significantly lower than the critical level causing additional derepression of GCN4 expression in eIF5G31R mutant to rescue its 3AT sensitivity. The overexpression of eIF1 improved expression of HIS4AUG allele and GCN4 transcript causing 3AT resistance, whereas overexpression of eIF1 resulted in diminished UUG codon recognition of HIS4UUG allele causing 3AT sensitivity, despite having higher GCN4 expression. This paper reports the critical role of HIS4 expression necessary in response to 3AT-induced starvation in the eIF5G31R mutant which is ostensibly not a direct target of 3AT inhibition.
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Affiliation(s)
- A Charles Antony
- School of Biological Sciences, National Institute of Science Education and Research, P.O. Jatni, Bhubaneswar, Khurda 752 050, India.
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17
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eIF1 Loop 2 interactions with Met-tRNA i control the accuracy of start codon selection by the scanning preinitiation complex. Proc Natl Acad Sci U S A 2018; 115:E4159-E4168. [PMID: 29666249 DOI: 10.1073/pnas.1800938115] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The eukaryotic 43S preinitiation complex (PIC), bearing initiator methionyl transfer RNA (Met-tRNAi) in a ternary complex (TC) with eukaryotic initiation factor 2 (eIF2)-GTP, scans the mRNA leader for an AUG codon in favorable context. AUG recognition evokes rearrangement from an open PIC conformation with TC in a "POUT" state to a closed conformation with TC more tightly bound in a "PIN" state. eIF1 binds to the 40S subunit and exerts a dual role of enhancing TC binding to the open PIC conformation while antagonizing the PIN state, necessitating eIF1 dissociation for start codon selection. Structures of reconstituted PICs reveal juxtaposition of eIF1 Loop 2 with the Met-tRNAi D loop in the PIN state and predict a distortion of Loop 2 from its conformation in the open complex to avoid a clash with Met-tRNAi We show that Ala substitutions in Loop 2 increase initiation at both near-cognate UUG codons and AUG codons in poor context. Consistently, the D71A-M74A double substitution stabilizes TC binding to 48S PICs reconstituted with mRNA harboring a UUG start codon, without affecting eIF1 affinity for 40S subunits. Relatively stronger effects were conferred by arginine substitutions; and no Loop 2 substitutions perturbed the rate of TC loading on scanning 40S subunits in vivo. Thus, Loop 2-D loop interactions specifically impede Met-tRNAi accommodation in the PIN state without influencing the POUT mode of TC binding; and Arg substitutions convert the Loop 2-tRNAi clash to an electrostatic attraction that stabilizes PIN and enhances selection of poor start codons in vivo.
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18
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Shirokikh NE, Preiss T. Translation initiation by cap-dependent ribosome recruitment: Recent insights and open questions. WILEY INTERDISCIPLINARY REVIEWS-RNA 2018; 9:e1473. [PMID: 29624880 DOI: 10.1002/wrna.1473] [Citation(s) in RCA: 91] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Revised: 02/02/2018] [Accepted: 02/14/2018] [Indexed: 12/14/2022]
Abstract
Gene expression universally relies on protein synthesis, where ribosomes recognize and decode the messenger RNA template by cycling through translation initiation, elongation, and termination phases. All aspects of translation have been studied for decades using the tools of biochemistry and molecular biology available at the time. Here, we focus on the mechanism of translation initiation in eukaryotes, which is remarkably more complex than prokaryotic initiation and is the target of multiple types of regulatory intervention. The "consensus" model, featuring cap-dependent ribosome entry and scanning of mRNA leader sequences, represents the predominantly utilized initiation pathway across eukaryotes, although several variations of the model and alternative initiation mechanisms are also known. Recent advances in structural biology techniques have enabled remarkable molecular-level insights into the functional states of eukaryotic ribosomes, including a range of ribosomal complexes with different combinations of translation initiation factors that are thought to represent bona fide intermediates of the initiation process. Similarly, high-throughput sequencing-based ribosome profiling or "footprinting" approaches have allowed much progress in understanding the elongation phase of translation, and variants of them are beginning to reveal the remaining mysteries of initiation, as well as aspects of translation termination and ribosomal recycling. A current view on the eukaryotic initiation mechanism is presented here with an emphasis on how recent structural and footprinting results underpin axioms of the consensus model. Along the way, we further outline some contested mechanistic issues and major open questions still to be addressed. This article is categorized under: Translation > Translation Mechanisms Translation > Translation Regulation RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.
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Affiliation(s)
- Nikolay E Shirokikh
- EMBL-Australia Collaborating Group, Department of Genome Sciences, The John Curtin School of Medical Research, The Australian National University, Canberra, Australia
- Victor Chang Cardiac Research Institute, Darlinghurst, Australia
| | - Thomas Preiss
- EMBL-Australia Collaborating Group, Department of Genome Sciences, The John Curtin School of Medical Research, The Australian National University, Canberra, Australia
- Victor Chang Cardiac Research Institute, Darlinghurst, Australia
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19
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Martin-Marcos P, Zhou F, Karunasiri C, Zhang F, Dong J, Nanda J, Kulkarni SD, Sen ND, Tamame M, Zeschnigk M, Lorsch JR, Hinnebusch AG. eIF1A residues implicated in cancer stabilize translation preinitiation complexes and favor suboptimal initiation sites in yeast. eLife 2017; 6:31250. [PMID: 29206102 PMCID: PMC5756025 DOI: 10.7554/elife.31250] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 12/04/2017] [Indexed: 11/13/2022] Open
Abstract
The translation pre-initiation complex (PIC) scans the mRNA for an AUG codon in favorable context, and AUG recognition stabilizes a closed PIC conformation. The unstructured N-terminal tail (NTT) of yeast eIF1A deploys five basic residues to contact tRNAi, mRNA, or 18S rRNA exclusively in the closed state. Interestingly, EIF1AX mutations altering the human eIF1A NTT are associated with uveal melanoma (UM). We found that substituting all five basic residues, and seven UM-associated substitutions, in yeast eIF1A suppresses initiation at near-cognate UUG codons and AUGs in poor context. Ribosome profiling of NTT substitution R13P reveals heightened discrimination against unfavorable AUG context genome-wide. Both R13P and K16D substitutions destabilize the closed complex at UUG codons in reconstituted PICs. Thus, electrostatic interactions involving the eIF1A NTT stabilize the closed conformation and promote utilization of suboptimal start codons. We predict UM-associated mutations alter human gene expression by increasing discrimination against poor initiation sites.
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Affiliation(s)
- Pilar Martin-Marcos
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States.,Instituto de Biología Funcional y Genómica, IBFG-CSIC, Universidad de Salamanca, Salamanca, Spain
| | - Fujun Zhou
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Charm Karunasiri
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Fan Zhang
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Jinsheng Dong
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Jagpreet Nanda
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Shardul D Kulkarni
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Neelam Dabas Sen
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Mercedes Tamame
- Instituto de Biología Funcional y Genómica, IBFG-CSIC, Universidad de Salamanca, Salamanca, Spain
| | - Michael Zeschnigk
- Institute of Human Genetics, University Duisburg-Essen, Essen, Germany.,Eye Cancer Research Group, Faculty of Medicine, University Duisburg-Essen, Essen, Germany
| | - Jon R Lorsch
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Development, National Institutes of Health, Bethesda, United States
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20
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Abstract
This review by Kearse and Wilusz discusses the profound impact of non-AUG start codons in eukaryotic translation. It describes how misregulation of non-AUG initiation events contributes to multiple human diseases, including cancer and neurodegeneration, and how modulation of non-AUG usage may represent a novel therapeutic strategy. Although it was long thought that eukaryotic translation almost always initiates at an AUG start codon, recent advancements in ribosome footprint mapping have revealed that non-AUG start codons are used at an astonishing frequency. These non-AUG initiation events are not simply errors but instead are used to generate or regulate proteins with key cellular functions; for example, during development or stress. Misregulation of non-AUG initiation events contributes to multiple human diseases, including cancer and neurodegeneration, and modulation of non-AUG usage may represent a novel therapeutic strategy. It is thus becoming increasingly clear that start codon selection is regulated by many trans-acting initiation factors as well as sequence/structural elements within messenger RNAs and that non-AUG translation has a profound impact on cellular states.
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Affiliation(s)
- Michael G Kearse
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, 19104 USA
| | - Jeremy E Wilusz
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, 19104 USA
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21
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Antony A C, Alone PV. Defect in the GTPase activating protein (GAP) function of eIF5 causes repression of GCN4 translation. Biochem Biophys Res Commun 2017; 486:1110-1115. [PMID: 28385532 DOI: 10.1016/j.bbrc.2017.04.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Accepted: 04/01/2017] [Indexed: 10/19/2022]
Abstract
In eukaryotes, the eIF5 protein plays an important role in translation start site selection by providing the GAP (GTPase activating protein) function. However, in yeast translation initiation fidelity defective eIF5G31R mutant causes preferential utilization of UUG as initiation codon and is termed as Suppressor of initiation codon (Sui-) phenotype due to its hyper GTPase activity. The eIF5G31R mutant dominantly represses GCN4 expression and confers sensitivity to 3-Amino-1,2,4-Trizole (3AT) induced starvation. The down-regulation of the GCN4 expression (Gcn- phenotype) in the eIF5G31R mutant was not because of leaky scanning defects; rather was due to the utilization of upUUG initiation codons at the 5' regulatory region present between uORF1 and the main GCN4 ORF.
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Affiliation(s)
- Charles Antony A
- School of Biological Sciences, National Institute of Science Education and Research Bhubaneswar, Constituent Institutes of Homi Bhabha National Institute (HBNI), P.O Jatni, Khurda 752050 India
| | - Pankaj V Alone
- School of Biological Sciences, National Institute of Science Education and Research Bhubaneswar, Constituent Institutes of Homi Bhabha National Institute (HBNI), P.O Jatni, Khurda 752050 India.
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22
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Obayashi E, Luna RE, Nagata T, Martin-Marcos P, Hiraishi H, Singh CR, Erzberger JP, Zhang F, Arthanari H, Morris J, Pellarin R, Moore C, Harmon I, Papadopoulos E, Yoshida H, Nasr ML, Unzai S, Thompson B, Aube E, Hustak S, Stengel F, Dagraca E, Ananbandam A, Gao P, Urano T, Hinnebusch AG, Wagner G, Asano K. Molecular Landscape of the Ribosome Pre-initiation Complex during mRNA Scanning: Structural Role for eIF3c and Its Control by eIF5. Cell Rep 2017; 18:2651-2663. [PMID: 28297669 PMCID: PMC5382721 DOI: 10.1016/j.celrep.2017.02.052] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 12/07/2016] [Accepted: 02/16/2017] [Indexed: 10/20/2022] Open
Abstract
During eukaryotic translation initiation, eIF3 binds the solvent-accessible side of the 40S ribosome and recruits the gate-keeper protein eIF1 and eIF5 to the decoding center. This is largely mediated by the N-terminal domain (NTD) of eIF3c, which can be divided into three parts: 3c0, 3c1, and 3c2. The N-terminal part, 3c0, binds eIF5 strongly but only weakly to the ribosome-binding surface of eIF1, whereas 3c1 and 3c2 form a stoichiometric complex with eIF1. 3c1 contacts eIF1 through Arg-53 and Leu-96, while 3c2 faces 40S protein uS15/S13, to anchor eIF1 to the scanning pre-initiation complex (PIC). We propose that the 3c0:eIF1 interaction diminishes eIF1 binding to the 40S, whereas 3c0:eIF5 interaction stabilizes the scanning PIC by precluding this inhibitory interaction. Upon start codon recognition, interactions involving eIF5, and ultimately 3c0:eIF1 association, facilitate eIF1 release. Our results reveal intricate molecular interactions within the PIC, programmed for rapid scanning-arrest at the start codon.
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Affiliation(s)
- Eiji Obayashi
- Shimane University School of Medicine, Izumo, Shimane 690-8504, Japan
| | - Rafael E Luna
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Takashi Nagata
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Pilar Martin-Marcos
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Hiroyuki Hiraishi
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Chingakham Ranjit Singh
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Jan Peter Erzberger
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, 8093 Zurich, Switzerland
| | - Fan Zhang
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Haribabu Arthanari
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Jacob Morris
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Riccardo Pellarin
- California Institute for Quantitative Biosciences, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Chelsea Moore
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Ian Harmon
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Evangelos Papadopoulos
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Hisashi Yoshida
- Graduate School of Medical Life Science, Yokohama City University, Tsurumi-ku, Yokohama 230-0045, Japan; Drug Design Group, Kanagawa Academy of Science and Technology, Takatsu-ku, Kawasaki 213-0012, Japan
| | - Mahmoud L Nasr
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Satoru Unzai
- Graduate School of Medical Life Science, Yokohama City University, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Brytteny Thompson
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Eric Aube
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Samantha Hustak
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Florian Stengel
- Department of Biology, Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Eddie Dagraca
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | | | - Philip Gao
- COBRE-PSF, University of Kansas, Lawrence, KS 66047, USA
| | - Takeshi Urano
- Shimane University School of Medicine, Izumo, Shimane 690-8504, Japan
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Katsura Asano
- Molecular Cellular Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, KS 66506, USA.
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23
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Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae. Genetics 2017; 203:65-107. [PMID: 27183566 DOI: 10.1534/genetics.115.186221] [Citation(s) in RCA: 93] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 02/24/2016] [Indexed: 12/18/2022] Open
Abstract
In this review, we provide an overview of protein synthesis in the yeast Saccharomyces cerevisiae The mechanism of protein synthesis is well conserved between yeast and other eukaryotes, and molecular genetic studies in budding yeast have provided critical insights into the fundamental process of translation as well as its regulation. The review focuses on the initiation and elongation phases of protein synthesis with descriptions of the roles of translation initiation and elongation factors that assist the ribosome in binding the messenger RNA (mRNA), selecting the start codon, and synthesizing the polypeptide. We also examine mechanisms of translational control highlighting the mRNA cap-binding proteins and the regulation of GCN4 and CPA1 mRNAs.
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Rps3/uS3 promotes mRNA binding at the 40S ribosome entry channel and stabilizes preinitiation complexes at start codons. Proc Natl Acad Sci U S A 2017; 114:E2126-E2135. [PMID: 28223523 DOI: 10.1073/pnas.1620569114] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The eukaryotic 43S preinitiation complex (PIC) bearing Met-tRNAiMet in a ternary complex (TC) with eukaryotic initiation factor (eIF)2-GTP scans the mRNA leader for an AUG codon in favorable "Kozak" context. AUG recognition provokes rearrangement from an open PIC conformation with TC bound in a state not fully engaged with the P site ("POUT") to a closed, arrested conformation with TC tightly bound in the "PIN" state. Yeast ribosomal protein Rps3/uS3 resides in the mRNA entry channel of the 40S subunit and contacts mRNA via conserved residues whose functional importance was unknown. We show that substitutions of these residues reduce bulk translation initiation and diminish initiation at near-cognate UUG start codons in yeast mutants in which UUG selection is abnormally high. Two such substitutions-R116D and R117D-also increase discrimination against an AUG codon in suboptimal Kozak context. Consistently, the Arg116 and Arg117 substitutions destabilize TC binding to 48S PICs reconstituted in vitro with mRNA harboring a UUG start codon, indicating destabilization of the closed PIN state with a UUG-anticodon mismatch. Using model mRNAs lacking contacts with either the mRNA entry or exit channels of the 40S subunit, we demonstrate that Arg116/Arg117 are crucial for stabilizing PIC-mRNA contacts at the entry channel, augmenting the function of eIF3 at both entry and exit channels. The corresponding residues in bacterial uS3 promote the helicase activity of the elongating ribosome, suggesting that uS3 contacts with mRNA enhance multiple phases of translation across different domains of life.
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Visweswaraiah J, Hinnebusch AG. Interface between 40S exit channel protein uS7/Rps5 and eIF2α modulates start codon recognition in vivo. eLife 2017; 6. [PMID: 28169832 PMCID: PMC5323038 DOI: 10.7554/elife.22572] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 02/06/2017] [Indexed: 12/26/2022] Open
Abstract
The eukaryotic pre-initiation complex (PIC) bearing the eIF2·GTP·Met-tRNAiMet ternary complex (TC) scans the mRNA for an AUG codon in favorable context. AUG recognition evokes rearrangement of the PIC from an open, scanning to a closed, arrested conformation. Cryo-EM reconstructions of yeast PICs suggest remodeling of the interface between 40S protein Rps5/uS7 and eIF2α between open and closed states; however, its importance was unknown. uS7 substitutions disrupting eIF2α contacts favored in the open complex increase initiation at suboptimal sites, and uS7-S223D stabilizes TC binding to PICs reconstituted with a UUG start codon, indicating inappropriate rearrangement to the closed state. Conversely, uS7-D215 substitutions, perturbing uS7-eIF2α interaction in the closed state, confer the opposite phenotypes of hyperaccuracy and (for D215L) accelerated TC dissociation from reconstituted PICs. Thus, remodeling of the uS7/eIF2α interface appears to stabilize first the open, and then the closed state of the PIC to promote accurate AUG selection in vivo. DOI:http://dx.doi.org/10.7554/eLife.22572.001
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Affiliation(s)
- Jyothsna Visweswaraiah
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, United States
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, United States
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26
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Llácer JL, Hussain T, Marler L, Aitken CE, Thakur A, Lorsch JR, Hinnebusch AG, Ramakrishnan V. Conformational Differences between Open and Closed States of the Eukaryotic Translation Initiation Complex. Mol Cell 2015. [PMID: 26212456 PMCID: PMC4534855 DOI: 10.1016/j.molcel.2015.06.033] [Citation(s) in RCA: 157] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Translation initiation in eukaryotes begins with the formation of a pre-initiation complex (PIC) containing the 40S ribosomal subunit, eIF1, eIF1A, eIF3, ternary complex (eIF2-GTP-Met-tRNAi), and eIF5. The PIC, in an open conformation, attaches to the 5′ end of the mRNA and scans to locate the start codon, whereupon it closes to arrest scanning. We present single particle cryo-electron microscopy (cryo-EM) reconstructions of 48S PICs from yeast in these open and closed states, at 6.0 Å and 4.9 Å, respectively. These reconstructions show eIF2β as well as a configuration of eIF3 that appears to encircle the 40S, occupying part of the subunit interface. Comparison of the complexes reveals a large conformational change in the 40S head from an open mRNA latch conformation to a closed one that constricts the mRNA entry channel and narrows the P site to enclose tRNAi, thus elucidating key events in start codon recognition. Structures of eukaryotic translation initiation complexes in open and closed states In the open complex the 40S head moves upward to open the mRNA entry channel latch Transition to closed state locks initiator tRNA in the P site base-paired with AUG The structures show how eIF3 contacts eIF2 and eIF1 on the 40S subunit interface
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Affiliation(s)
- Jose L Llácer
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK
| | | | - Laura Marler
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Colin Echeverría Aitken
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Anil Thakur
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jon R Lorsch
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - V Ramakrishnan
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
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Visweswaraiah J, Pittman Y, Dever TE, Hinnebusch AG. The β-hairpin of 40S exit channel protein Rps5/uS7 promotes efficient and accurate translation initiation in vivo. eLife 2015; 4:e07939. [PMID: 26134896 PMCID: PMC4513230 DOI: 10.7554/elife.07939] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2015] [Accepted: 07/01/2015] [Indexed: 11/13/2022] Open
Abstract
The eukaryotic 43S pre-initiation complex bearing tRNAi(Met) scans the mRNA leader for an AUG start codon in favorable context. Structural analyses revealed that the β-hairpin of 40S protein Rps5/uS7 protrudes into the 40S mRNA exit-channel, contacting the eIF2∙GTP∙Met-tRNAi ternary complex (TC) and mRNA context nucleotides; but its importance in AUG selection was unknown. We identified substitutions in β-strand-1 and C-terminal residues of yeast Rps5 that reduced bulk initiation, conferred 'leaky-scanning' of AUGs; and lowered initiation fidelity by exacerbating the effect of poor context of the eIF1 AUG codon to reduce eIF1 abundance. Consistently, the β-strand-1 substitution greatly destabilized the 'PIN' conformation of TC binding to reconstituted 43S·mRNA complexes in vitro. Other substitutions in β-hairpin loop residues increased initiation fidelity and destabilized PIN at UUG, but not AUG start codons. We conclude that the Rps5 β-hairpin is as crucial as soluble initiation factors for efficient and accurate start codon recognition.
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Affiliation(s)
- Jyothsna Visweswaraiah
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, United States
| | - Yvette Pittman
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, United States
| | - Thomas E Dever
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, United States
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, United States
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Browning KS, Bailey-Serres J. Mechanism of cytoplasmic mRNA translation. THE ARABIDOPSIS BOOK 2015; 13:e0176. [PMID: 26019692 PMCID: PMC4441251 DOI: 10.1199/tab.0176] [Citation(s) in RCA: 144] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Protein synthesis is a fundamental process in gene expression that depends upon the abundance and accessibility of the mRNA transcript as well as the activity of many protein and RNA-protein complexes. Here we focus on the intricate mechanics of mRNA translation in the cytoplasm of higher plants. This chapter includes an inventory of the plant translational apparatus and a detailed review of the translational processes of initiation, elongation, and termination. The majority of mechanistic studies of cytoplasmic translation have been carried out in yeast and mammalian systems. The factors and mechanisms of translation are for the most part conserved across eukaryotes; however, some distinctions are known to exist in plants. A comprehensive understanding of the complex translational apparatus and its regulation in plants is warranted, as the modulation of protein production is critical to development, environmental plasticity and biomass yield in diverse ecosystems and agricultural settings.
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Affiliation(s)
- Karen S. Browning
- Department of Molecular Biosciences and Institute for Cell and Molecular Biology, University of Texas at Austin, Austin TX 78712-0165
- Both authors contributed equally to this work
| | - Julia Bailey-Serres
- Department of Botany and Plant Sciences and Center for Plant Cell Biology, University of California, Riverside, CA, 92521 USA
- Both authors contributed equally to this work
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29
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Sinvani H, Haimov O, Svitkin Y, Sonenberg N, Tamarkin-Ben-Harush A, Viollet B, Dikstein R. Translational tolerance of mitochondrial genes to metabolic energy stress involves TISU and eIF1-eIF4GI cooperation in start codon selection. Cell Metab 2015; 21:479-92. [PMID: 25738462 DOI: 10.1016/j.cmet.2015.02.010] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Revised: 10/22/2014] [Accepted: 02/09/2015] [Indexed: 11/30/2022]
Abstract
Protein synthesis is a major energy-consuming process, which is rapidly repressed upon energy stress by AMPK. How energy deficiency affects translation of mRNAs that cope with the stress response is poorly understood. We found that mitochondrial genes remain translationally active upon energy deprivation. Surprisingly, inhibition of translation is partially retained in AMPKα1/AMPKα2 knockout cells. Mitochondrial mRNAs are enriched with TISU, a translation initiator of short 5' UTR, which confers resistance specifically to energy stress. Purified 48S preinitiation complex is sufficient for initiation via TISU AUG, when preceded by a short 5' UTR. eIF1 stimulates TISU but inhibits non-TISU-directed initiation. Remarkably, eIF4GI shares this activity and also interacts with eIF1. Furthermore, eIF4F is released upon 48S formation on TISU. These findings describe a specialized translation tolerance mechanism enabling continuous translation of TISU genes under energy stress and reveal that a key step in start codon selection of short 5' UTR is eIF4F release.
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Affiliation(s)
- Hadar Sinvani
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Ora Haimov
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yuri Svitkin
- Department of Biochemistry and Goodman Cancer Centre, McGill University, Montreal, QC H3A 1A3, Canada
| | - Nahum Sonenberg
- Department of Biochemistry and Goodman Cancer Centre, McGill University, Montreal, QC H3A 1A3, Canada
| | - Ana Tamarkin-Ben-Harush
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Benoit Viollet
- University Paris Descartes, Institut Cochin, 75014 Paris, France
| | - Rivka Dikstein
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
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Hussain T, Llácer JL, Fernández IS, Munoz A, Martin-Marcos P, Savva CG, Lorsch JR, Hinnebusch AG, Ramakrishnan V. Structural changes enable start codon recognition by the eukaryotic translation initiation complex. Cell 2014; 159:597-607. [PMID: 25417110 PMCID: PMC4217140 DOI: 10.1016/j.cell.2014.10.001] [Citation(s) in RCA: 143] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 08/15/2014] [Accepted: 10/01/2014] [Indexed: 11/03/2022]
Abstract
During eukaryotic translation initiation, initiator tRNA does not insert fully into the P decoding site on the 40S ribosomal subunit. This conformation (POUT) is compatible with scanning mRNA for the AUG start codon. Base pairing with AUG is thought to promote isomerization to a more stable conformation (PIN) that arrests scanning and promotes dissociation of eIF1 from the 40S subunit. Here, we present a cryoEM reconstruction of a yeast preinitiation complex at 4.0 Å resolution with initiator tRNA in the PIN state, prior to eIF1 release. The structure reveals stabilization of the codon-anticodon duplex by the N-terminal tail of eIF1A, changes in the structure of eIF1 likely instrumental in its subsequent release, and changes in the conformation of eIF2. The mRNA traverses the entire mRNA cleft and makes connections to the regulatory domain of eIF2?, eIF1A, and ribosomal elements that allow recognition of context nucleotides surrounding the AUG codon.
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Affiliation(s)
| | - Jose L Llácer
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK
| | | | - Antonio Munoz
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Pilar Martin-Marcos
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | | | - Jon R Lorsch
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - V Ramakrishnan
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
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Sokabe M, Fraser CS. Human eukaryotic initiation factor 2 (eIF2)-GTP-Met-tRNAi ternary complex and eIF3 stabilize the 43 S preinitiation complex. J Biol Chem 2014; 289:31827-31836. [PMID: 25246524 DOI: 10.1074/jbc.m114.602870] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The formation of a stable 43 S preinitiation complex (PIC) must occur to enable successful mRNA recruitment. However, the contributions of eIF1, eIF1A, eIF3, and the eIF2-GTP-Met-tRNAi ternary complex (TC) in stabilizing the 43 S PIC are poorly defined. We have reconstituted the human 43 S PIC and used fluorescence anisotropy to systematically measure the affinity of eIF1, eIF1A, and eIF3j in the presence of different combinations of 43 S PIC components. Our data reveal a complicated network of interactions that result in high affinity binding of all 43 S PIC components with the 40 S subunit. Human eIF1 and eIF1A bind cooperatively to the 40 S subunit, revealing an evolutionarily conserved interaction. Negative cooperativity is observed between the binding of eIF3j and the binding of eIF1, eIF1A, and TC with the 40 S subunit. To overcome this, eIF3 dramatically increases the affinity of eIF1 and eIF3j for the 40 S subunit. Recruitment of TC also increases the affinity of eIF1 for the 40 S subunit, but this interaction has an important indirect role in increasing the affinity of eIF1A for the 40 S subunit. Together, our data provide a more complete thermodynamic framework of the human 43 S PIC and reveal important interactions between its components to maintain its stability.
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Affiliation(s)
- Masaaki Sokabe
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, California 95616
| | - Christopher S Fraser
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, California 95616.
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32
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Saini AK, Nanda JS, Martin-Marcos P, Dong J, Zhang F, Bhardwaj M, Lorsch JR, Hinnebusch AG. Eukaryotic translation initiation factor eIF5 promotes the accuracy of start codon recognition by regulating Pi release and conformational transitions of the preinitiation complex. Nucleic Acids Res 2014; 42:9623-40. [PMID: 25114053 PMCID: PMC4150770 DOI: 10.1093/nar/gku653] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
eIF5 is the GTPase activating protein (GAP) for the eIF2 · GTP · Met-tRNAi (Met) ternary complex with a critical role in initiation codon selection. Previous work suggested that the eIF5 mutation G31R/SUI5 elevates initiation at UUG codons by increasing GAP function. Subsequent work implicated eIF5 in rearrangement of the preinitiation complex (PIC) from an open, scanning conformation to a closed state at AUG codons, from which Pi is released from eIF2 · GDP · Pi. To identify eIF5 functions crucial for accurate initiation, we investigated the consequences of G31R on GTP hydrolysis and Pi release, and the effects of intragenic G31R suppressors on these reactions, and on the partitioning of PICs between open and closed states. eIF5-G31R altered regulation of Pi release, accelerating it at UUG while decreasing it at AUG codons, consistent with its ability to stabilize the closed complex at UUG. Suppressor G62S mitigates both defects of G31R, accounting for its efficient suppression of UUG initiation in G31R,G62S cells; however suppressor M18V impairs GTP hydrolysis with little effect on PIC conformation. The strong defect in GTP hydrolysis conferred by M18V likely explains its broad suppression of Sui(-) mutations in numerous factors. We conclude that both of eIF5's functions, regulating Pi release and stabilizing the closed PIC conformation, contribute to stringent AUG selection in vivo.
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Affiliation(s)
- Adesh K Saini
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Jagpreet S Nanda
- Shoolini University of Biotechnology and Management Sciences, Department of Biotechnology, Bajhol, Solan, Himachal Pradesh 173229, India
| | - Pilar Martin-Marcos
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Jinsheng Dong
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Fan Zhang
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Monika Bhardwaj
- Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Jon R Lorsch
- Shoolini University of Biotechnology and Management Sciences, Department of Biotechnology, Bajhol, Solan, Himachal Pradesh 173229, India
| | - Alan G Hinnebusch
- Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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Conserved residues in yeast initiator tRNA calibrate initiation accuracy by regulating preinitiation complex stability at the start codon. Genes Dev 2014; 28:502-20. [PMID: 24589778 PMCID: PMC3950347 DOI: 10.1101/gad.236547.113] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Eukaryotic initiator tRNA (tRNAi) contains several highly conserved, unique sequence features, yet their importance in accurate start codon selection is unknown. Using genetic and biochemical analyses, Dong et al. show that conserved bases throughout tRNAi, from the anticodon stem to the acceptor stem, play key roles in ensuring the fidelity of start codon recognition. This work delineates specific molecular functions for signature initiator tRNA residues and establishes their importance for initiation accuracy in living eukaryotic cells. Eukaryotic initiator tRNA (tRNAi) contains several highly conserved unique sequence features, but their importance in accurate start codon selection was unknown. Here we show that conserved bases throughout tRNAi, from the anticodon stem to acceptor stem, play key roles in ensuring the fidelity of start codon recognition in yeast cells. Substituting the conserved G31:C39 base pair in the anticodon stem with different pairs reduces accuracy (the Sui− [suppressor of initiation codon] phenotype), whereas eliminating base pairing increases accuracy (the Ssu− [suppressor of Sui−] phenotype). The latter defect is fully suppressed by a Sui− substitution of T-loop residue A54. These genetic data are paralleled by opposing effects of Sui− and Ssu− substitutions on the stability of methionylated tRNAi (Met-tRNAi) binding (in the ternary complex [TC] with eIF2-GTP) to reconstituted preinitiation complexes (PICs). Disrupting the C3:G70 base pair in the acceptor stem produces a Sui− phenotype and also reduces the rate of TC binding to 40S subunits in vitro and in vivo. Both defects are suppressed by an Ssu− substitution in eIF1A that stabilizes the open/POUT conformation of the PIC that exists prior to start codon recognition. Our data indicate that these signature sequences of tRNAi regulate accuracy by distinct mechanisms, promoting the open/POUT conformation of the PIC (for C3:G70) or destabilizing the closed/PIN state (for G31:C39 and A54) that is critical for start codon recognition.
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