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Dang TT, Kim MJ, Lee YY, Le HT, Kim KH, Nam S, Hyun SH, Kim HL, Chung SW, Chung HT, Jho EH, Yoshida H, Kim K, Park CY, Lee MS, Back SH. Phosphorylation of EIF2S1 (eukaryotic translation initiation factor 2 subunit alpha) is indispensable for nuclear translocation of TFEB and TFE3 during ER stress. Autophagy 2023; 19:2111-2142. [PMID: 36719671 PMCID: PMC10283430 DOI: 10.1080/15548627.2023.2173900] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [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: 10/27/2022] [Revised: 01/21/2023] [Accepted: 01/24/2023] [Indexed: 02/01/2023] Open
Abstract
There are diverse links between macroautophagy/autophagy pathways and unfolded protein response (UPR) pathways under endoplasmic reticulum (ER) stress conditions to restore ER homeostasis. Phosphorylation of EIF2S1/eIF2α is an important mechanism that can regulate all three UPR pathways through transcriptional and translational reprogramming to maintain cellular homeostasis and overcome cellular stresses. In this study, to investigate the roles of EIF2S1 phosphorylation in regulation of autophagy during ER stress, we used EIF2S1 phosphorylation-deficient (A/A) cells in which residue 51 was mutated from serine to alanine. A/A cells exhibited defects in several steps of autophagic processes (such as autophagosome and autolysosome formation) that are regulated by the transcriptional activities of the autophagy master transcription factors TFEB and TFE3 under ER stress conditions. EIF2S1 phosphorylation was required for nuclear translocation of TFEB and TFE3 during ER stress. In addition, EIF2AK3/PERK, PPP3/calcineurin-mediated dephosphorylation of TFEB and TFE3, and YWHA/14-3-3 dissociation were required for their nuclear translocation, but were insufficient to induce their nuclear retention during ER stress. Overexpression of the activated ATF6/ATF6α form, XBP1s, and ATF4 differentially rescued defects of TFEB and TFE3 nuclear translocation in A/A cells during ER stress. Consequently, overexpression of the activated ATF6 or TFEB form more efficiently rescued autophagic defects, although XBP1s and ATF4 also displayed an ability to restore autophagy in A/A cells during ER stress. Our results suggest that EIF2S1 phosphorylation is important for autophagy and UPR pathways, to restore ER homeostasis and reveal how EIF2S1 phosphorylation connects UPR pathways to autophagy.Abbreviations: A/A: EIF2S1 phosphorylation-deficient; ACTB: actin beta; Ad-: adenovirus-; ATF6: activating transcription factor 6; ATZ: SERPINA1/α1-antitrypsin with an E342K (Z) mutation; Baf A1: bafilomycin A1; BSA: bovine serum albumin; CDK4: cyclin dependent kinase 4; CDK6: cyclin dependent kinase 6; CHX: cycloheximide; CLEAR: coordinated lysosomal expression and regulation; Co-IP: coimmunoprecipitation; CTSB: cathepsin B; CTSD: cathepsin D; CTSL: cathepsin L; DAPI: 4',6-diamidino-2-phenylindole dihydrochloride; DMEM: Dulbecco's modified Eagle's medium; DMSO: dimethyl sulfoxide; DTT: dithiothreitol; EBSS: Earle's Balanced Salt Solution; EGFP: enhanced green fluorescent protein; EIF2S1/eIF2α: eukaryotic translation initiation factor 2 subunit alpha; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; ERAD: endoplasmic reticulum-associated degradation; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; FBS: fetal bovine serum; gRNA: guide RNA; GSK3B/GSK3β: glycogen synthase kinase 3 beta; HA: hemagglutinin; Hep: immortalized hepatocyte; IF: immunofluorescence; IRES: internal ribosome entry site; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LMB: leptomycin B; LPS: lipopolysaccharide; MAP1LC3A/B/LC3A/B: microtubule associated protein 1 light chain 3 alpha/beta; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MEFs: mouse embryonic fibroblasts; MFI: mean fluorescence intensity; MTORC1: mechanistic target of rapamycin kinase complex 1; NES: nuclear export signal; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; OE: overexpression; PBS: phosphate-buffered saline; PLA: proximity ligation assay; PPP3/calcineurin: protein phosphatase 3; PTM: post-translational modification; SDS: sodium dodecyl sulfate; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SEM: standard error of the mean; TEM: transmission electron microscopy; TFE3: transcription factor E3; TFEB: transcription factor EB; TFs: transcription factors; Tg: thapsigargin; Tm: tunicamycin; UPR: unfolded protein response; WB: western blot; WT: wild-type; Xbp1s: spliced Xbp1; XPO1/CRM1: exportin 1.
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Affiliation(s)
- Thao Thi Dang
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
| | - Mi-Jeong Kim
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
| | - Yoon Young Lee
- Department of Biological Sciences, School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, 44919, Korea
| | - Hien Thi Le
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
| | - Kook Hwan Kim
- Severance Biomedical Research Institute, Yonsei University College of Medicine, 03722, Seoul, Korea
| | - Somi Nam
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
| | - Seung Hwa Hyun
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
| | - Hong Lim Kim
- Integrative Research Support Center, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Su Wol Chung
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
| | - Hun Taeg Chung
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
| | - Eek-Hoon Jho
- Department of Life Science, University of Seoul, Seoul, Korea
| | - Hiderou Yoshida
- Department of Molecular Biochemistry, Graduate School of Life Science, University of Hyogo, 678-1297, Hyogo, Japan
| | - Kyoungmi Kim
- Department of Biomedical Sciences and Department of Physiology, Korea University College of Medicine, 02841, Seoul, Korea
| | - Chan Young Park
- Department of Biological Sciences, School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, 44919, Korea
| | - Myung-Shik Lee
- Department of Integrated Biomedical Science & Division of Endocrinology, Department of Internal Medicine, SIMS (Soonchunhyang Institute of Medi-bio Science) & Soonchunhyang University Hospital, Soonchunhyang University, 31151, Cheonan, Korea
| | - Sung Hoon Back
- School of Biological Sciences, University of Ulsan, Ulsan, 44610, Korea
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Wang B, Zhang J, Liu X, Chai Q, Lu X, Yao X, Yang Z, Sun L, Johnson SF, Schwartz RC, Zheng YH. Protein disulfide isomerases (PDIs) negatively regulate ebolavirus structural glycoprotein expression in the endoplasmic reticulum (ER) via the autophagy-lysosomal pathway. Autophagy 2022; 18:2350-2367. [PMID: 35130104 PMCID: PMC9542513 DOI: 10.1080/15548627.2022.2031381] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [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: 06/24/2021] [Revised: 01/14/2022] [Accepted: 01/17/2022] [Indexed: 02/09/2023] Open
Abstract
Zaire ebolavirus (EBOV) causes a severe hemorrhagic fever in humans and non-human primates with high morbidity and mortality. EBOV infection is dependent on its structural glycoprotein (GP), but high levels of GP expression also trigger cell rounding, detachment, and downregulation of many surface molecules that is thought to contribute to its high pathogenicity. Thus, EBOV has evolved an RNA editing mechanism to reduce its GP expression and increase its fitness. We now report that the GP expression is also suppressed at the protein level in cells by protein disulfide isomerases (PDIs). Although PDIs promote oxidative protein folding by catalyzing correct disulfide formation in the endoplasmic reticulum (ER), PDIA3/ERp57 adversely triggered the GP misfolding by targeting GP cysteine residues and activated the unfolded protein response (UPR). Abnormally folded GP was targeted by ER-associated protein degradation (ERAD) machinery and, unexpectedly, was degraded via the macroautophagy/autophagy-lysosomal pathway, but not the proteasomal pathway. PDIA3 also decreased the GP expression from other ebolavirus species but increased the GP expression from Marburg virus (MARV), which is consistent with the observation that MARV-GP does not cause cell rounding and detachment, and MARV does not regulate its GP expression via RNA editing during infection. Furthermore, five other PDIs also had a similar inhibitory activity to EBOV-GP. Thus, PDIs negatively regulate ebolavirus glycoprotein expression, which balances the viral life cycle by maximizing their infection but minimizing their cellular effect. We suggest that ebolaviruses hijack the host protein folding and ERAD machinery to increase their fitness via reticulophagy during infection.Abbreviations: 3-MA: 3-methyladenine; 4-PBA: 4-phenylbutyrate; ACTB: β-actin; ATF: activating transcription factor; ATG: autophagy-related; BafA1: bafilomycin A1; BDBV: Bundibugyo ebolavirus; CALR: calreticulin; CANX: calnexin; CHX: cycloheximide; CMA: chaperone-mediated autophagy; ConA: concanamycin A; CRISPR: clusters of regularly interspaced short palindromic repeats; Cas9: CRISPR-associated protein 9; dsRNA: double-stranded RNA; EBOV: Zaire ebolavirus; EDEM: ER degradation enhancing alpha-mannosidase like protein; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; Env: envelope glycoprotein; ER: endoplasmic reticulum; ERAD: ER-associated protein degradation; ERN1/IRE1: endoplasmic reticulum to nucleus signaling 1; GP: glycoprotein; HA: hemagglutinin; HDAC6: histone deacetylase 6; HMM: high-molecular-mass; HIV-1: human immunodeficiency virus type 1; HSPA5/BiP: heat shock protein family A (Hsp70) member 5; IAV: influenza A virus; IP: immunoprecipitation; KIF: kifenesine; Lac: lactacystin; LAMP: lysosomal associated membrane protein; MAN1B1/ERManI: mannosidase alpha class 1B member 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARV: Marburg virus; MLD: mucin-like domain; NHK/SERPINA1: alpha1-antitrypsin variant null (Hong Kong); NTZ: nitazoxanide; PDI: protein disulfide isomerase; RAVV: Ravn virus; RESTV: Reston ebolavirus; SARS-CoV: severe acute respiratory syndrome coronavirus; SBOV: Sudan ebolavirus; sGP: soluble GP; SQSTM1/p62: sequestosome 1; ssGP: small soluble GP; TAFV: Taï Forest ebolavirus; TIZ: tizoxanide; TGN: thapsigargin; TLD: TXN (thioredoxin)-like domain; Ub: ubiquitin; UPR: unfolded protein response; VLP: virus-like particle; VSV: vesicular stomatitis virus; WB: Western blotting; WT: wild-type; XBP1: X-box binding protein 1.
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Affiliation(s)
- Bin Wang
- CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
- MSD (Ningbo) Animal Health Technology Co., Ltd, Ningbo, China
| | - Jing Zhang
- CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Xin Liu
- CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
- College of Animal Science and Veterinary Medicine, Heilongjiang Bayi Agricultural University, Daqing, China
| | - Qingqing Chai
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Xiaoran Lu
- CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Xiaoyu Yao
- CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Zhichang Yang
- Department of Chemistry, Michigan State University, East Lansing, Michigan, USA
| | - Liangliang Sun
- Department of Chemistry, Michigan State University, East Lansing, Michigan, USA
| | - Silas F. Johnson
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Richard C Schwartz
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Yong-Hui Zheng
- CAAS-Michigan State University Joint Laboratory of Innate Immunity, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
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Jennings MD, Pavitt GD. Quantifying the Binding of Fluorescently Labeled Guanine Nucleotides and Initiator tRNA to Eukaryotic Translation Initiation Factor 2. Methods Mol Biol 2022; 2428:89-99. [PMID: 35171475 DOI: 10.1007/978-1-0716-1975-9_6] [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] [Indexed: 06/14/2023]
Abstract
The translation initiation factor eIF2 is critical for protein synthesis initiation, and its regulation is central to the integrated stress response (ISR). eIF2 is a G protein, and the activity is regulated by its GDP or GTP-binding status, such that only GTP-bound eIF2 has high affinity for initiator methionyl tRNA. In the ISR, regulatory signaling reduces the availability of eIF2-GTP and so downregulates protein synthesis initiation in cells. Fluorescence spectroscopy can be used as an analytical tool to study protein-ligand interactions in vitro. Here we describe methods to purify eIF2 and assays of its activity, employing analogs of GDP, GTP, and methionyl initiator tRNA ligands to accurately measure their binding affinities.
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Affiliation(s)
- Martin D Jennings
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, UK
| | - Graham D Pavitt
- Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, UK.
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Tomsic J, Caserta E, Pon CL, Gualerzi CO. Weakening the IF2-fMet-tRNA Interaction Suppresses the Lethal Phenotype Caused by GTPase Inactivation. Int J Mol Sci 2021; 22:ijms222413238. [PMID: 34948034 PMCID: PMC8709274 DOI: 10.3390/ijms222413238] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [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: 10/31/2021] [Revised: 12/07/2021] [Accepted: 12/07/2021] [Indexed: 01/12/2023] Open
Abstract
Substitution of the conserved Histidine 448 present in one of the three consensus elements characterizing the guanosine nucleotide binding domain (IF2 G2) of Escherichia coli translation initiation factor IF2 resulted in impaired ribosome-dependent GTPase activity which prevented IF2 dissociation from the ribosome, caused a severe protein synthesis inhibition, and yielded a dominant lethal phenotype. A reduced IF2 affinity for the ribosome was previously shown to suppress this lethality. Here, we demonstrate that also a reduced IF2 affinity for fMet-tRNA can suppress this dominant lethal phenotype and allows IF2 to support faithful translation in the complete absence of GTP hydrolysis. These results strengthen the premise that the conformational changes of ribosome, IF2, and fMet-tRNA occurring during the late stages of translation initiation are thermally driven and that the energy generated by IF2-dependent GTP hydrolysis is not required for successful translation initiation and that the dissociation of the interaction between IF2 C2 and the acceptor end of fMet-tRNA, which represents the last tie anchoring the factor to the ribosome before the formation of an elongation-competent 70S complex, is rate limiting for both the adjustment of fMet-tRNA in a productive P site and the IF2 release from the ribosome.
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Affiliation(s)
- Jerneja Tomsic
- Laboratory of Genetics, Department of Bioscience and Biotechnology, University of Camerino, 62032 Camerino, Italy; (J.T.); (E.C.); (C.L.P.)
- City of Hope Comprehensive Cancer Center, Duarte, CA 91010, USA
| | - Enrico Caserta
- Laboratory of Genetics, Department of Bioscience and Biotechnology, University of Camerino, 62032 Camerino, Italy; (J.T.); (E.C.); (C.L.P.)
- City of Hope Comprehensive Cancer Center, Duarte, CA 91010, USA
| | - Cynthia L. Pon
- Laboratory of Genetics, Department of Bioscience and Biotechnology, University of Camerino, 62032 Camerino, Italy; (J.T.); (E.C.); (C.L.P.)
| | - Claudio O. Gualerzi
- Laboratory of Genetics, Department of Bioscience and Biotechnology, University of Camerino, 62032 Camerino, Italy; (J.T.); (E.C.); (C.L.P.)
- Correspondence: ; Tel.: +39-3391602957
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Nakamoto JA, Evangelista W, Vinogradova DS, Konevega A, Spurio R, Fabbretti A, Milón P. The dynamic cycle of bacterial translation initiation factor IF3. Nucleic Acids Res 2021; 49:6958-6970. [PMID: 34161576 PMCID: PMC8266586 DOI: 10.1093/nar/gkab522] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [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: 04/05/2021] [Revised: 06/01/2021] [Accepted: 06/09/2021] [Indexed: 11/14/2022] Open
Abstract
Initiation factor IF3 is an essential protein that enhances the fidelity and speed of bacterial mRNA translation initiation. Here, we describe the dynamic interplay between IF3 domains and their alternative binding sites using pre-steady state kinetics combined with molecular modelling of available structures of initiation complexes. Our results show that IF3 accommodates its domains at velocities ranging over two orders of magnitude, responding to the binding of each 30S ligand. IF1 and IF2 promote IF3 compaction and the movement of the C-terminal domain (IF3C) towards the P site. Concomitantly, the N-terminal domain (IF3N) creates a pocket ready to accept the initiator tRNA. Selection of the initiator tRNA is accompanied by a transient accommodation of IF3N towards the 30S platform. Decoding of the mRNA start codon displaces IF3C away from the P site and rate limits translation initiation. 70S initiation complex formation brings IF3 domains in close proximity to each other prior to dissociation and recycling of the factor for a new round of translation initiation. Altogether, our results describe the kinetic spectrum of IF3 movements and highlight functional transitions of the factor that ensure accurate mRNA translation initiation.
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Affiliation(s)
- Jose A Nakamoto
- Laboratory of Applied Biophysics and Biochemistry, Centre for Research and Innovation, Health Sciences Faculty, Universidad Peruana de Ciencias Aplicadas (UPC), Lima 15023, Peru
| | - Wilfredo Evangelista
- Laboratory of Applied Biophysics and Biochemistry, Centre for Research and Innovation, Health Sciences Faculty, Universidad Peruana de Ciencias Aplicadas (UPC), Lima 15023, Peru
| | - Daria S Vinogradova
- Petersburg Nuclear Physics Institute, NRC ‘Kurchatov Institute’, Gatchina 188300, Russia
- NanoTemper Technologies Rus, Saint Petersburg 191167, Russia
| | - Andrey L Konevega
- Petersburg Nuclear Physics Institute, NRC ‘Kurchatov Institute’, Gatchina 188300, Russia
- NRC ‘Kurchatov Institute’, Moscow 123182, Russia
- Peter the Great St. Petersburg Polytechnic University, Saint Petersburg 195251, Russia
| | - Roberto Spurio
- Laboratory of Genetics, School of Biosciences and Veterinary Medicine, University of Camerino, Camerino 62032, Italy
| | - Attilio Fabbretti
- Laboratory of Genetics, School of Biosciences and Veterinary Medicine, University of Camerino, Camerino 62032, Italy
| | - Pohl Milón
- Laboratory of Applied Biophysics and Biochemistry, Centre for Research and Innovation, Health Sciences Faculty, Universidad Peruana de Ciencias Aplicadas (UPC), Lima 15023, Peru
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Abstract
Initiation of protein synthesis in eukaryotes is a complex process requiring more than 12 different initiation factors, comprising over 30 polypeptide chains. The functions of many of these factors have been established in great detail; however, the precise role of some of them and their mechanism of action is still not well understood. Eukaryotic initiation factor 2A (eIF2A) is a single chain 65 kDa protein that was initially believed to serve as the functional homologue of prokaryotic IF2, since eIF2A and IF2 catalyze biochemically similar reactions, i.e., they stimulate initiator Met-tRNAi binding to the small ribosomal subunit. However, subsequent identification of a heterotrimeric 126 kDa factor, eIF2 (α,β,γ) showed that this factor, and not eIF2A, was primarily responsible for the binding of Met-tRNAi to 40S subunit in eukaryotes. It was found however, that eIF2A can promote recruitment of Met-tRNAi to 40S/mRNA complexes under conditions of inhibition of eIF2 activity (eIF2α-phosphorylation), or its absence. eIF2A does not function in major steps in the initiation process, but is suggested to act at some minor/alternative initiation events such as re-initiation, internal initiation, or non-AUG initiation, important for translational control of specific mRNAs. This review summarizes our current understanding of the eIF2A structure and function.
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Affiliation(s)
- Anton A. Komar
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological and Environmental Sciences, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA;
| | - William C. Merrick
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA;
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Delle Fratte S, Piubelli C, Domenici E. Development of a High-Throughput Scintillation Proximity Assay for the Identification of C-Domain Translational Initiation Factor 2 Inhibitors. ACTA ACUST UNITED AC 2016; 7:541-6. [PMID: 14599352 DOI: 10.1177/1087057102238628] [Citation(s) in RCA: 6] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Translational initiation factor 2 (IF2) is the largest of the 3 factors required for translation initiation in prokaryotes and has been shown to be essential in Escherichia coli. It stimulates the binding of fMet-tRNAfMet to the 30S ribosomal subunit in the presence of GTP. The selectivity is achieved through specific recognition of the tRNAfMet blocked α-amino group. IF2 is composed of 3 structural domains: N-domain, whose function is not known; G-domain, which contains the GTP/GDP binding site and the GTPase catalytic center; and C-domain, which recognizes and binds fMet-tRNAfMet. Its activity is strictly bacteria specific and highly conserved among prokaryotes. So far, antibiotics targeting IF2 function are not known, and this makes it an ideal target for new drugs with mechanisms of resistance not yet developed. A few assays have been developed in the past, which allow the detection of IF2 activity either directly or indirectly. In both instances, the assays are based on radioactive detection and do not allow for high throughput because of the need for separation or solvent extraction steps. The authors describe a novel biochemical assay for IF2 that exploits the molecular recognition of fMet-tRNAfMet by the C-domain. The assay is based on the incubation of biotinyl-IF2 with fMet-tRNAfMet and the subsequent capture of the radiolabeled complex by streptavidin-coated beads, exploiting the scintillation proximity assay (SPA) technology. The assay has been designed in an automatable, homogeneous, miniaturized fashion suitable for high-throughput screening and is rapid, sensitive, and robust to dimethyl sulfoxide (DMSO) up to 10% v/v. The assay, used to screen a limited chemical collection of about 5000 compounds and a subset of compounds originated by a 2-D substructural search, has shown to be able to detect potential IF2 inhibitors.
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Leonard A, Paton AW, El-Quadi M, Paton JC, Fazal F. Preconditioning with endoplasmic reticulum stress ameliorates endothelial cell inflammation. PLoS One 2014; 9:e110949. [PMID: 25356743 PMCID: PMC4214695 DOI: 10.1371/journal.pone.0110949] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 09/17/2014] [Indexed: 01/11/2023] Open
Abstract
Endoplasmic Reticulum (ER) stress, caused by disturbance in ER homeostasis, has been implicated in several pathological conditions such as ischemic injury, neurodegenerative disorders, metabolic diseases and more recently in inflammatory conditions. Our present study aims at understanding the role of ER stress in endothelial cell (EC) inflammation, a critical event in the pathogenesis of acute lung injury (ALI). We found that preconditioning human pulmonary artery endothelial cells (HPAEC) to ER stress either by depleting ER chaperone and signaling regulator BiP using siRNA, or specifically cleaving (inactivating) BiP using subtilase cytotoxin (SubAB), alleviates EC inflammation. The two approaches adopted to abrogate BiP function induced ATF4 protein expression and the phosphorylation of eIF2α, both markers of ER stress, which in turn resulted in blunting the activation of NF-κB, and restoring endothelial barrier integrity. Pretreatment of HPAEC with BiP siRNA inhibited thrombin-induced IκBα degradation and its resulting downstream signaling pathway involving NF-κB nuclear translocation, DNA binding, phosphorylation at serine536, transcriptional activation and subsequent expression of adhesion molecules. However, TNFα-mediated NF-κB signaling was unaffected upon BiP knockdown. In an alternative approach, SubAB-mediated inactivation of NF-κB was independent of IκBα degradation. Mechanistic analysis revealed that pretreatment of EC with SubAB interfered with the binding of the liberated NF-κB to the DNA, thereby resulting in reduced expression of adhesion molecules, cytokines and chemokines. In addition, both knockdown and inactivation of BiP stimulated actin cytoskeletal reorganization resulting in restoration of endothelial permeability. Together our studies indicate that BiP plays a central role in EC inflammation and injury via its action on NF-κB activation and regulation of vascular permeability.
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Affiliation(s)
- Antony Leonard
- Department of Pediatrics, Lung Biology and Disease Program, University of Rochester School of Medicine and Dentistry, Rochester, New York, United States of America
| | - Adrienne W. Paton
- Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, Australia
| | - Monaliza El-Quadi
- Department of Pediatrics, Lung Biology and Disease Program, University of Rochester School of Medicine and Dentistry, Rochester, New York, United States of America
| | - James C. Paton
- Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, Australia
| | - Fabeha Fazal
- Department of Pediatrics, Lung Biology and Disease Program, University of Rochester School of Medicine and Dentistry, Rochester, New York, United States of America
- * E-mail:
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Kuzmenko A, Atkinson GC, Levitskii S, Zenkin N, Tenson T, Hauryliuk V, Kamenski P. Mitochondrial translation initiation machinery: conservation and diversification. Biochimie 2013; 100:132-40. [PMID: 23954798 PMCID: PMC3978653 DOI: 10.1016/j.biochi.2013.07.024] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 07/29/2013] [Indexed: 11/29/2022]
Abstract
The highly streamlined mitochondrial genome encodes almost exclusively a handful of transmembrane components of the respiratory chain complex. In order to ensure the correct assembly of the respiratory chain, the products of these genes must be produced in the correct stoichiometry and inserted into the membrane, posing a unique challenge to the mitochondrial translational system. In this review we describe the proteins orchestrating mitochondrial translation initiation: bacterial-like general initiation factors mIF2 and mIF3, as well as mitochondria-specific components – mRNA-specific translational activators and mRNA-nonspecific accessory initiation factors. We consider how the fast rate of evolution in these organelles has not only created a system that is divergent from that of its bacterial ancestors, but has led to a huge diversity in lineage specific mechanistic features of mitochondrial translation initiation among eukaryotes. Mitochondrially-encoded proteins are mostly respiratory chain components. The mitochondrial translation system is thus organized in a very specific way. Initiation involves mRNA-specific activators and bacteria-like initiation factors. We show that Saccharomyces cerevisiae Aim23p is a functional ortholog of bacterial IF3. We review the lineage specific features of mitochondrial translation initiation.
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Affiliation(s)
- Anton Kuzmenko
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia; Molecular Biology Department, Faculty of Biology, M.V. Lomonosov Moscow State University, 1/12 Leninskie Gory, 119991 Moscow, Russia
| | - Gemma C Atkinson
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia
| | - Sergey Levitskii
- Molecular Biology Department, Faculty of Biology, M.V. Lomonosov Moscow State University, 1/12 Leninskie Gory, 119991 Moscow, Russia
| | - Nikolay Zenkin
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4AX, United Kingdom
| | - Tanel Tenson
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia
| | - Vasili Hauryliuk
- University of Tartu, Institute of Technology, Nooruse 1, Tartu, Estonia; Department of Molecular Biology, Umeå University, Umeå, Sweden; Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, Sweden.
| | - Piotr Kamenski
- Molecular Biology Department, Faculty of Biology, M.V. Lomonosov Moscow State University, 1/12 Leninskie Gory, 119991 Moscow, Russia.
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10
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Zhang H, Hu Y, Yang B, Xue F, Wang C, Kang Z, Ji W. Isolation and characterization of a wheat IF2 homolog required for innate immunity to stripe rust. Plant Cell Rep 2013; 32:591-600. [PMID: 23397275 DOI: 10.1007/s00299-013-1390-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 01/15/2013] [Indexed: 06/01/2023]
Abstract
The wheat eIF2 homolog, TaIF2, is induced by the stripe rust pathogen CYR 32 at an early stage of inoculation and is related to the innate immunity resistance level in wheat. The initiation of translation represents a critical control point in the regulation of gene expression in all organisms. We previously identified an upregulated EST S186 (EL773056) from an SSH-cDNA library of the Shaanmai 139 strain of wheat (Triticum aestivum) infected with Puccinia striiformis (Pst). In the present work, we isolated a cDNA clone and identified it as a wheat IF2 homolog. This cDNA consisted of 1,314 nucleotides and contained an open reading frame of 795 nucleotides encoding a polypeptide of 254 amino acids. The amino acids represent a conserved domain in EF-Tu, mtIF2-II, and mtIF2-Ivc. The alignment result showed that it maybe a partial cDNA of the initiation factor 2/eukaryotic initiation factor 5B (IF2/eIF5B) superfamily gene. Paradoxically, results of a Swiss-model analysis suggesting a low QMEAN Z-score implied that it was a membrane protein. Quantitative RT-PCR studies confirmed that the wheat eIF2 (TaIF2) homolog was differentially expressed in three near-isogenic lines. Critical time points for the induction of resistance by inoculation with Pst CYR32 in YrSM139-1B + YrSM139-2D immune resistance genotype occurred at 1 and 3 dpi (days post-infection). RNAi test showed that the inoculated BSMV-IF2 leaves of Shaanmai 139 showed obvious cell death after 15 days of inoculation with CYR 32. qRT-PCR analysis of the target gene in cDNA samples isolated from BSMV-IF2-Pst, BSMV-0-Pst and Pst infected leaves confirmed that the expression of TaIF2 is suppressed by BSMV-IF2 at 3 dpi. This suggested that TaIF2/eIF5B plays an important role in the mechanism of innate immunity to stripe rust pathogen.
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Affiliation(s)
- Hong Zhang
- State Key Laboratory of Crop Stress Biology in Arid Areas (Northwest A&F University), Yangling, 712100, China.
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11
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Overcash RF, Chappell VA, Green T, Geyer CB, Asch AS, Ruiz-Echevarría MJ. Androgen signaling promotes translation of TMEFF2 in prostate cancer cells via phosphorylation of the α subunit of the translation initiation factor 2. PLoS One 2013; 8:e55257. [PMID: 23405127 PMCID: PMC3566213 DOI: 10.1371/journal.pone.0055257] [Citation(s) in RCA: 18] [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: 07/23/2012] [Accepted: 12/27/2012] [Indexed: 01/21/2023] Open
Abstract
The type I transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2), is expressed mainly in brain and prostate. Expression of TMEFF2 is deregulated in prostate cancer, suggesting a role in this disease, but the molecular mechanism(s) involved in this effect are not clear. Although androgens promote tmeff2 transcription, androgen delivery to castrated animals carrying CWR22 xenografts increases TMEFF2 protein levels in the absence of mRNA changes, suggesting that TMEFF2 may also be post-transcriptionally regulated. Here we show that translation of TMEFF2 is regulated by androgens. Addition of physiological concentrations of dihydrotestosterone (DHT) to prostate cancer cell lines increases translation of endogenous TMEFF2 or transfected TMEFF2-Luciferase fusions, and this effect requires the presence of upstream open reading frames (uORFs) in the 5′-untranslated region (5′-UTR) of TMEFF2. Using chemical and siRNA inhibition of the androgen receptor (AR), we show that the androgen effect on TMEFF2 translation is mediated by the AR. Importantly, DHT also promotes phosphorylation of the α subunit of the translation initiation factor 2 (eIF2α) in an AR-dependent manner, paralleling the effect on TMEFF2 translation. Moreover, endoplasmic reticulum (ER) stress conditions, which promote eIF2α phosphorylation, also stimulate TMEFF2 translation. These results indicate that androgen signaling promotes eIF2α phosphorylation and subsequent translation of TMEFF2 via a mechanism that requires uORFs in the 5′-UTR of TMEFF2.
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Affiliation(s)
- Ryan F. Overcash
- Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
| | - Vesna A. Chappell
- Department of Anatomy and Cell Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
| | - Thomas Green
- Department of Internal Medicine, Division of Hematology/Oncology. Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
| | - Christopher B. Geyer
- Department of Anatomy and Cell Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
| | - Adam S. Asch
- Department of Internal Medicine, Division of Hematology/Oncology. Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Maria J. Ruiz-Echevarría
- Department of Anatomy and Cell Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
- Department of Internal Medicine, Division of Hematology/Oncology. Brody School of Medicine at East Carolina University, Greenville, North Carolina, United States of America
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- * E-mail:
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12
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Madison KE, Abdelmeguid MR, Jones-Foster EN, Nakai H. A new role for translation initiation factor 2 in maintaining genome integrity. PLoS Genet 2012; 8:e1002648. [PMID: 22536160 PMCID: PMC3334882 DOI: 10.1371/journal.pgen.1002648] [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] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Accepted: 02/24/2012] [Indexed: 11/25/2022] Open
Abstract
Escherichia coli translation initiation factor 2 (IF2) performs the unexpected function of promoting transition from recombination to replication during bacteriophage Mu transposition in vitro, leading to initiation by replication restart proteins. This function has suggested a role of IF2 in engaging cellular restart mechanisms and regulating the maintenance of genome integrity. To examine the potential effect of IF2 on restart mechanisms, we characterized its influence on cellular recovery following DNA damage by methyl methanesulfonate (MMS) and UV damage. Mutations that prevent expression of full-length IF2-1 or truncated IF2-2 and IF2-3 isoforms affected cellular growth or recovery following DNA damage differently, influencing different restart mechanisms. A deletion mutant (del1) expressing only IF2-2/3 was severely sensitive to growth in the presence of DNA-damaging agent MMS. Proficient as wild type in repairing DNA lesions and promoting replication restart upon removal of MMS, this mutant was nevertheless unable to sustain cell growth in the presence of MMS; however, growth in MMS could be partly restored by disruption of sulA, which encodes a cell division inhibitor induced during replication fork arrest. Moreover, such characteristics of del1 MMS sensitivity were shared by restart mutant priA300, which encodes a helicase-deficient restart protein. Epistasis analysis indicated that del1 in combination with priA300 had no further effects on cellular recovery from MMS and UV treatment; however, the del2/3 mutation, which allows expression of only IF2-1, synergistically increased UV sensitivity in combination with priA300. The results indicate that full-length IF2, in a function distinct from truncated forms, influences the engagement or activity of restart functions dependent on PriA helicase, allowing cellular growth when a DNA–damaging agent is present. Translation Initiation Factor 2 (IF2) is a bacterial protein that plays an essential role in the initiation of protein synthesis. As such, it not only has an important influence on cellular growth but also is subject to regulation in response to physiological conditions such as nutritional deprivation. Biochemical characterization of IF2's function in replicating movable genetic elements has suggested a new role in the maintenance of genome integrity, potentially regulating replication restart. The parasitic elements exploit the cellular replication restart system to duplicate themselves as they transpose to new positions of the chromosome. In this process, IF2 makes way for action of restart proteins, which assemble replication enzymes for initiation of DNA synthesis. For the bacterial cell, the restart system is the means by which it copes with accidents that result in arrest of chromosomal replication, promoting resumption of replication. We present evidence for an IF2 function associated with restart proteins, allowing chromosomal replication in the presence of DNA–damaging agents. As the IF2 function is a highly conserved one found in all organisms, the findings have implications for understanding the maintenance of genome integrity with respect to physiological status, which can be sensed by the translation apparatus.
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Affiliation(s)
| | | | | | - Hiroshi Nakai
- Department of Biochemistry and Molecular and Cellular Biology, Georgetown University Medical Center, Washington, D.C, United States of America
- * E-mail:
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13
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Abstract
Nutrient sensing and the capacity to respond to starvation is tightly regulated as a means of cell survival. Among the features of the starvation response are induction of both translational repression and autophagy. Despite the fact that intracellular parasite like Toxoplasma gondii within a host cell predicted to be nutrient rich, they encode genes involved in both translational repression and autophagy. We therefore examined the consequence of starvation, a classic trigger of autophagy, on intracellular parasites. As expected, starvation results in the activation of the translational repression system as evidenced by elevation of phosphorylated TgIF2α (TgIF2α-P). Surprisingly, we also observe a rapid and selective fragmentation of the single parasite mitochondrion that leads irreversibly to parasite death. This profound effect was dependent primarily on the limitation of amino acids and involved signalling by the parasite TOR homologue. Notably, the effective blockade of mitochondrial fragmentation by the autophagy inhibitor 3-methyl adenine (3-MA) suggests an autophagic mechanism. In the absence of a documented apoptotic cascade in T. gondii, the data suggest that autophagy is the primary mechanism of programmed cell death in T. gondii and potentially other related parasites.
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Affiliation(s)
- Debasish Ghosh
- Department of Microbiology, Immunology and Molecular Genetics; University of Kentucky College of Medicine, Lexington KY 40536, USA
| | - Julia L. Walton
- Department of Microbiology, Immunology and Molecular Genetics; University of Kentucky College of Medicine, Lexington KY 40536, USA
| | - Paul D. Roepe
- Departments of Chemistry, Biochemistry and Cellular and Molecular Biology, Georgetown University, Washington DC. 20057, USA
| | - Anthony P. Sinai
- Department of Microbiology, Immunology and Molecular Genetics; University of Kentucky College of Medicine, Lexington KY 40536, USA
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14
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Mikolajka A, Liu H, Chen Y, Starosta AL, Márquez V, Ivanova M, Cooperman BS, Wilson DN. Differential effects of thiopeptide and orthosomycin antibiotics on translational GTPases. ACTA ACUST UNITED AC 2011; 18:589-600. [PMID: 21609840 DOI: 10.1016/j.chembiol.2011.03.010] [Citation(s) in RCA: 31] [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] [Received: 02/06/2011] [Revised: 03/07/2011] [Accepted: 03/14/2011] [Indexed: 11/18/2022]
Abstract
The ribosome is a major target in the bacterial cell for antibiotics. Here, we dissect the effects that the thiopeptide antibiotics thiostrepton (ThS) and micrococcin (MiC) as well as the orthosomycin antibiotic evernimicin (Evn) have on translational GTPases. We demonstrate that, like ThS, MiC is a translocation inhibitor, and that the activation by MiC of the ribosome-dependent GTPase activity of EF-G is dependent on the presence of the ribosomal proteins L7/L12 as well as the G' subdomain of EF-G. In contrast, Evn does not inhibit translocation but is a potent inhibitor of back-translocation as well as IF2-dependent 70S-initiation complex formation. Collectively, these results shed insight not only into fundamental aspects of translation but also into the unappreciated specificities of these classes of translational inhibitors.
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15
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Bylund GO, Nord S, Lövgren JM, Wikström PM. Alterations in the β flap and β' dock domains of the RNA polymerase abolish NusA-mediated feedback regulation of the metY-nusA-infB operon. J Bacteriol 2011; 193:4113-22. [PMID: 21685293 PMCID: PMC3147696 DOI: 10.1128/jb.00196-11] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [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: 02/11/2011] [Accepted: 06/04/2011] [Indexed: 11/20/2022] Open
Abstract
The RimM protein in Escherichia coli is important for the in vivo maturation of 30S ribosomal subunits and a ΔrimM mutant grows poorly due to assembly and translational defects. These deficiencies are suppressed partially by mutations that increase the synthesis of another assembly protein, RbfA, encoded by the metY-nusA-infB operon. Among these suppressors are mutations in nusA that impair the NusA-mediated negative-feedback regulation at internal intrinsic transcriptional terminators of the metY-nusA-infB operon. We describe here the isolation of two new mutations, one in rpoB and one in rpoC (encoding the β and β' subunits of the RNA polymerase, respectively), that increase the synthesis of RbfA by preventing NusA from stimulating termination at the internal intrinsic transcriptional terminators of the metY-nusA-infB operon. The rpoB2063 mutation changed the isoleucine in position 905 of the β flap-tip helix to a serine, while the rpoC2064 mutation duplicated positions 415 to 416 (valine-isoleucine) at the base of the β' dock domain. These findings support previously published in vitro results, which have suggested that the β flap-tip helix and β' dock domain at either side of the RNA exit tunnel mediate the binding to NusA during transcriptional pausing and termination.
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Affiliation(s)
| | | | | | - P. Mikael Wikström
- Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden
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16
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Mitkevich VA, Ermakov A, Kulikova AA, Tankov S, Shyp V, Soosaar A, Tenson T, Makarov AA, Ehrenberg M, Hauryliuk V. Thermodynamic characterization of ppGpp binding to EF-G or IF2 and of initiator tRNA binding to free IF2 in the presence of GDP, GTP, or ppGpp. J Mol Biol 2010; 402:838-46. [PMID: 20713063 DOI: 10.1016/j.jmb.2010.08.016] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [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: 06/16/2010] [Revised: 08/08/2010] [Accepted: 08/09/2010] [Indexed: 11/17/2022]
Abstract
In addition to their natural substrates GDP and GTP, the bacterial translational GTPases initiation factor (IF) 2 and elongation factor G (EF-G) interact with the alarmone molecule guanosine tetraphosphate (ppGpp), which leads to GTPase inhibition. We have used isothermal titration calorimetry to determine the affinities of ppGpp for IF2 and EF-G at a temperature interval of 5-25 °C. We find that ppGpp has a higher affinity for IF2 than for EF-G (1.7-2.8 μM K(d)versus 9.1-13.9 μM K(d) at 10-25 °C), suggesting that during stringent response in vivo, IF2 is more responsive to ppGpp than to EF-G. We investigated the effects of ppGpp, GDP, and GTP on IF2 interactions with fMet-tRNA(fMet) demonstrating that IF2 binds to initiator tRNA with submicromolar K(d) and that affinity is altered by the G nucleotides only slightly. This--in conjunction with earlier reports on IF2 interactions with fMet-tRNA(fMet) in the context of the 30S initiation complex, where ppGpp was suggested to strongly inhibit fMet-tRNA(fMet) binding and GTP was suggested to strongly promote fMet-tRNA(fMet) binding--sheds new light on the mechanisms of the G-nucleotide-regulated fMet-tRNA(fMet) selection.
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Affiliation(s)
- Vladimir A Mitkevich
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Vavilov St. 32, Moscow 119991, Russia
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17
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Zorzet A, Pavlov MY, Nilsson AI, Ehrenberg M, Andersson DI. Error-prone initiation factor 2 mutations reduce the fitness cost of antibiotic resistance. Mol Microbiol 2010; 75:1299-313. [PMID: 20132454 PMCID: PMC2859245 DOI: 10.1111/j.1365-2958.2010.07057.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [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] [Accepted: 01/12/2010] [Indexed: 11/27/2022]
Abstract
Mutations in the fmt gene (encoding formyl methionine transferase) that eliminate formylation of initiator tRNA (Met-tRNA(i)) confer resistance to the novel antibiotic class of peptide deformylase inhibitors (PDFIs) while concomitantly reducing bacterial fitness. Here we show in Salmonella typhimurium that novel mutations in initiation factor 2 (IF2) located outside the initiator tRNA binding domain can partly restore fitness of fmt mutants without loss of antibiotic resistance. Analysis of initiation of protein synthesis in vitro showed that with non-formylated Met-tRNA(i) IF2 mutants initiated much faster than wild-type IF2, whereas with formylated fMet-tRNA(i) the initiation rates were similar. Moreover, the increase in initiation rates with Met-tRNA(i) conferred by IF2 mutations in vitro correlated well with the increase in growth rate conferred by the same mutations in vivo, suggesting that the mutations in IF2 compensate formylation deficiency by increasing the rate of in vivo initiation with Met-tRNA(i). IF2 mutants had also a high propensity for erroneous initiation with elongator tRNAs in vitro, which could account for their reduced fitness in vivo in a formylation-proficient strain. More generally, our results suggest that bacterial protein synthesis is mRNA-limited and that compensatory mutations in IF2 could increase the persistence of PDFI-resistant bacteria in clinical settings.
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Affiliation(s)
- Anna Zorzet
- Department of Medical Biochemistry and Microbiology, Uppsala UniversityBox 582, SE-751 23 Uppsala, Sweden
| | - Michael Y Pavlov
- Department of Cell and Molecular Biology, Uppsala UniversityBox 596, SE-751 24 Uppsala, Sweden
| | - Annika I Nilsson
- Department of Medical Biochemistry and Microbiology, Uppsala UniversityBox 582, SE-751 23 Uppsala, Sweden
| | - Måns Ehrenberg
- Department of Cell and Molecular Biology, Uppsala UniversityBox 596, SE-751 24 Uppsala, Sweden
| | - Dan I Andersson
- Department of Medical Biochemistry and Microbiology, Uppsala UniversityBox 582, SE-751 23 Uppsala, Sweden
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18
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Gaur R, Grasso D, Datta PP, Krishna PDV, Das G, Spencer A, Agrawal RK, Spremulli L, Varshney U. A single mammalian mitochondrial translation initiation factor functionally replaces two bacterial factors. Mol Cell 2008; 29:180-90. [PMID: 18243113 DOI: 10.1016/j.molcel.2007.11.021] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [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: 06/27/2007] [Revised: 08/30/2007] [Accepted: 11/05/2007] [Indexed: 11/19/2022]
Abstract
The mechanism of translation in eubacteria and organelles is thought to be similar. In eubacteria, the three initiation factors IF1, IF2, and IF3 are vital. Although the homologs of IF2 and IF3 are found in mammalian mitochondria, an IF1 homolog has never been detected. Here, we show that bovine mitochondrial IF2 (IF2(mt)) complements E. coli containing a deletion of the IF2 gene (E. coli DeltainfB). We find that IF1 is no longer essential in an IF2(mt)-supported E. coli DeltainfB strain. Furthermore, biochemical and molecular modeling data show that a conserved insertion of 37 amino acids in the IF2(mt) substitutes for the function of IF1. Deletion of this insertion from IF2(mt) supports E. coli for the essential function of IF2. However, in this background, IF1 remains essential. These observations provide strong evidence that a single factor (IF2(mt)) in mammalian mitochondria performs the functions of two eubacterial factors, IF1 and IF2.
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Affiliation(s)
- Rahul Gaur
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
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19
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Burakovskiĭ DE, Smirnova AS, Lesniak DV, Kiparisov SV, Leonov AA, Sergiev PV, Bogdanov AA, Dontsova OA. [Interaction of 23S ribosomal RNA helices 89 and 91 of Escherichia coli contributes to the activity of IF2 but is insignificant for elongation factors functioning]. Mol Biol (Mosk) 2007; 41:1031-1041. [PMID: 18318122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The non-canonical base-pair C2475/G2529 joins helices 89 and 91 of the 23S rRNA in the large subunit of E. coli ribosomes. These nucleotides are located at the "crossroads" between the peptidyl transferase center, the sarcin-ricin loop and the GTPase-associated center. We probed the functional role of nucleotides C2475/G2529 by the mutations C2475G, C2475G/G2529C and deltaA2471/U2479 of 23S rRNA. All these mutations had no influence on the elongation factors activity but had different effects on the cell growth, 23S rRNA conformation and translation initiation. C2475G/G2529C and C2475G mutations led to more or less substantial decrease in IF2.GDPNP binding to the ribosomes, and IF2-assisted initiation complex formation. Ribosome-dependent GTPase activity of IF2 was enhanced by both C2475G/G2529C and C2475G mutations. Mutation deltaA2471/U2479 has no influence on IF2.GDPNP binding to the ribosome, but reduces IF2-dependent formation of initiation complex and the ribosome-dependent GTPase activity. Thus, the contact between helices 89 and 91 is important for efficient IF2 functioning in translation initiation.
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20
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Nikonov O, Stolboushkina E, Nikulin A, Hasenöhrl D, Bläsi U, Manstein DJ, Fedorov R, Garber M, Nikonov S. New insights into the interactions of the translation initiation factor 2 from archaea with guanine nucleotides and initiator tRNA. J Mol Biol 2007; 373:328-36. [PMID: 17825838 DOI: 10.1016/j.jmb.2007.07.048] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [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: 05/07/2007] [Revised: 07/11/2007] [Accepted: 07/20/2007] [Indexed: 10/23/2022]
Abstract
Heterotrimeric a/eIF2alphabetagamma (archaeal homologue of the eukaryotic translation initiation factor 2 with alpha, beta and gamma subunits) delivers charged initiator tRNA (tRNAi) to the small ribosomal subunit. In this work, we determined the structures of aIF2gamma from the archaeon Sulfolobus solfataricus in the nucleotide-free and GDP-bound forms. Comparison of the free, GDP and Gpp(NH)p-Mg2+ forms of aIF2gamma revealed a sequence of conformational changes upon GDP and GTP binding. Our results show that the affinity of GDP to the G domain of the gamma subunit is higher than that of Gpp(NH)p. In analyzing a pyrophosphate molecule binding to domain II of the gamma subunit, we found a cleft that is very suitable for the acceptor stem of tRNA accommodation. It allows the suggestion of an alternative position for Met-tRNA i Met on the alphagamma intersubunit dimer, at variance with a recently published one. In the model reported here, the acceptor stem of the tRNAi is approximately perpendicular to that of tRNA in the ternary complex elongation factor Tu-Gpp(NH)p-tRNA. According to our analysis, the elbow and T stem of Met-tRNA i Met in this position should make extensive contact with the alpha subunit of aIF2. Thus, this model is in good agreement with experimental data showing that the alpha subunit of aIF2 is necessary for the stable interaction of aIF2gamma with Met-tRNA i Met.
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Affiliation(s)
- Oleg Nikonov
- Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russian Federation.
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21
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Grigoriadou C, Marzi S, Kirillov S, Gualerzi CO, Cooperman BS. A quantitative kinetic scheme for 70 S translation initiation complex formation. J Mol Biol 2007; 373:562-72. [PMID: 17868692 PMCID: PMC2083556 DOI: 10.1016/j.jmb.2007.07.032] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [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: 05/06/2007] [Revised: 07/12/2007] [Accepted: 07/13/2007] [Indexed: 10/23/2022]
Abstract
Association of the 30 S initiation complex (30SIC) and the 50 S ribosomal subunit, leading to formation of the 70 S initiation complex (70SIC), is a critical step of the translation initiation pathway. The 70SIC contains initiator tRNA, fMet-tRNA(fMet), bound in the P (peptidyl)-site in response to the AUG start codon. We have formulated a quantitative kinetic scheme for the formation of an active 70SIC from 30SIC and 50 S subunits on the basis of parallel rapid kinetics measurements of GTP hydrolysis, Pi release, light-scattering, and changes in fluorescence intensities of fluorophore-labeled IF2 and fMet-tRNA(f)(Met). According to this scheme, an initially formed labile 70 S complex, which promotes rapid IF2-dependent GTP hydrolysis, either dissociates reversibly into 30 S and 50 S subunits or is converted to a more stable form, leading to 70SIC formation. The latter process takes place with intervening conformational changes of ribosome-bound IF2 and fMet-tRNA(fMet), which are monitored by spectral changes of fluorescent derivatives of IF2 and fMet-tRNA(fMet). The availability of such a scheme provides a useful framework for precisely elucidating the mechanisms by which substituting the non-hydrolyzable analog GDPCP for GTP or adding thiostrepton inhibit formation of a productive 70SIC. GDPCP does not affect stable 70 S formation, but perturbs fMet-tRNA(fMet) positioning in the P-site. In contrast, thiostrepton severely retards stable 70 S formation, but allows normal binding of fMet-tRNA(fMet)(prf20) to the P-site.
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Affiliation(s)
- Christina Grigoriadou
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
| | - Stefano Marzi
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
| | - Stanislas Kirillov
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
- Petersburg Nuclear Physics Institute RAS, 188300 Gatchina, Russia
| | - Claudio O. Gualerzi
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
| | - Barry S. Cooperman
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
- Corresponding author:
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22
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Grigoriadou C, Marzi S, Pan D, Gualerzi CO, Cooperman BS. The translational fidelity function of IF3 during transition from the 30 S initiation complex to the 70 S initiation complex. J Mol Biol 2007; 373:551-61. [PMID: 17868695 PMCID: PMC2083563 DOI: 10.1016/j.jmb.2007.07.031] [Citation(s) in RCA: 48] [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: 05/06/2007] [Revised: 07/12/2007] [Accepted: 07/13/2007] [Indexed: 10/23/2022]
Abstract
IF3 has a fidelity function in the initiation of translation, inducing the dissociation of fMet-tRNA(fMet) from the 30 S initiation complexes (30SIC) containing a non-canonical initiation triplet (e.g. AUU) in place of a canonical initiation triplet (e.g., AUG). IF2 has a complementary role, selectively promoting initiator tRNA binding to the ribosome. Here, we used parallel rapid kinetics measurements of GTP hydrolysis, Pi release, light-scattering, and changes in intensities of fluorophore-labeled IF2 and fMet-tRNA(fMet) to determine the effects on both 30SIC formation and 30SIC conversion to 70 S initiation complexes (70SIC) of (a) substituting AUG with AUU, and/or (b) omitting IF3, and/or (c) replacing GTP with the non-hydrolyzable analog GDPCP. We demonstrate that the presence or absence of IF3 has, at most, minor effects on the rate of 30SIC formation using either AUG or AUU as the initiation codon, and conclude that the high affinity of IF2 for both 30 S subunit and initiator tRNA overrides any perturbation of the codon-anticodon interaction resulting from AUU for AUG substitution. In contrast, replacement of AUG by AUU leads to a dramatic reduction in the rate of 70SIC formation from 30SIC upon addition of 50 S subunits. Interpreting our results in the framework of a quantitative kinetic scheme leads to the conclusion that, within the overall process of 70SIC formation, the step most affected by substituting AUU for AUG involves the conversion of an initially labile 70 S ribosome into a more stable complex. In the absence of IF3, the difference between AUG and AUU largely disappears, with each initiation codon affording rapid 70SIC formation, leading to the hypothesis that it is the rate of IF3 dissociation from the 70 S ribosome during IC70S formation that is critical to its fidelity function.
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Affiliation(s)
- Christina Grigoriadou
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
| | - Stefano Marzi
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
| | - Dongli Pan
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Claudio O. Gualerzi
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
| | - Barry S. Cooperman
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
- Corresponding author:
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23
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Helgstrand M, Mandava CS, Mulder FAA, Liljas A, Sanyal S, Akke M. The Ribosomal Stalk Binds to Translation Factors IF2, EF-Tu, EF-G and RF3 via a Conserved Region of the L12 C-terminal Domain. J Mol Biol 2007; 365:468-79. [PMID: 17070545 DOI: 10.1016/j.jmb.2006.10.025] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.1] [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: 07/04/2006] [Revised: 09/27/2006] [Accepted: 10/09/2006] [Indexed: 11/30/2022]
Abstract
Efficient protein synthesis in bacteria requires initiation factor 2 (IF2), elongation factors Tu (EF-Tu) and G (EF-G), and release factor 3 (RF3), each of which catalyzes a major step of translation in a GTP-dependent fashion. Previous reports have suggested that recruitment of factors to the ribosome and subsequent GTP hydrolysis involve the dimeric protein L12, which forms a flexible "stalk" on the ribosome. Using heteronuclear NMR spectroscopy we demonstrate that L12 binds directly to the factors IF2, EF-Tu, EF-G, and RF3 from Escherichia coli, and map the region of L12 involved in these interactions. Factor-dependent chemical shift changes show that all four factors bind to the same region of the C-terminal domain of L12. This region includes three strictly conserved residues, K70, L80, and E82, and a set of highly conserved residues, including V66, A67, V68 and G79. Upon factor binding, all NMR signals from the C-terminal domain become broadened beyond detection, while those from the N-terminal domain are virtually unaffected, implying that the C-terminal domain binds to the factor, while the N-terminal domain dimer retains its rotational freedom mediated by the flexible hinge between the two domains. Factor-dependent variations in linewidths further reveal that L12 binds to each factor with a dissociation constant in the millimolar range in solution. These results indicate that the L12-factor complexes will be highly populated on the ribosome, because of the high local concentration of ribosome-bound factor with respect to L12.
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Affiliation(s)
- Magnus Helgstrand
- Department of Biophysical Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden
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24
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Abstract
All living organisms utilize ribosomes to translate messenger RNA into proteins. Initiation of translation, the process of bringing together mRNA, initiator transfer RNA, and the ribosome, is therefore of critical importance to all living things. Two protein factors, IF1 (a/eIF1A) and IF2 (a/eIF5B), are conserved among all three kingdoms of life and have been called universal initiation factors (Roll-Mecak et al., 2001). Recent X-ray, NMR and cryo-EM structures of the universal factors, alone and in complex with eubacterial ribosomes, point to the structural homology among the initiation factors and initiation complexes. Taken together with genomic and functional evidence, the structural studies allow us to predict some features of eukaryotic and archaeal initiation complexes. Although initiation of translation in eukaryotes and archaea requires more initiation factors than in eubacteria we propose the existence of a common denominator initiation complex with structural and functional homology across all kingdoms of life.
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Affiliation(s)
- Gregory S Allen
- Howard Hughes Medical Institute, Health Research, Inc., Wadsworth Center, Empire State Plaza, Albany, NY 12201, USA
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25
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Hayashi R, Ueda T, Farwell MA, Takeuchi N. Nuclear respiratory factor 2 activates transcription of human mitochondrial translation initiation factor 2 gene. Mitochondrion 2006; 7:195-203. [PMID: 17161026 DOI: 10.1016/j.mito.2006.10.005] [Citation(s) in RCA: 7] [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] [Received: 08/24/2006] [Revised: 10/20/2006] [Accepted: 10/26/2006] [Indexed: 11/18/2022]
Abstract
We studied the transcriptional regulation of the human mitochondrial translation initiation factor 2 (IF2mt) gene. The minimal promoter region for the human IF2mt gene contains binding sites for Nuclear Respiratory Factor 2 (NRF-2), which is often involved in the transcription of mitochondrial-related genes. Electrophoresis mobility shift assay (EMSA) analyses indicated that NRF-2alpha/beta binds to the IF2mt promoter. Reporter assays, where HEK293T cells were co-transfected with an NRF-2alpha/beta-expressing vector and/or an IF2mt promoter reporter vector, revealed that NRF-2 trans-activates the IF2mt promoter. NRF-2 sites were also found in the promoters of several other mitochondrial translation factors, which suggests NRF-2 may play a key role in the regulation of mitochondrial protein synthesis.
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Affiliation(s)
- Rippei Hayashi
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Building FSB-401, 5-1-5 Kashiwanoha, Kashiwa, Chiba Prefecture 277-8562, Japan
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26
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Milon P, Tischenko E, Tomšic J, Caserta E, Folkers G, La Teana A, Rodnina MV, Pon CL, Boelens R, Gualerzi CO. The nucleotide-binding site of bacterial translation initiation factor 2 (IF2) as a metabolic sensor. Proc Natl Acad Sci U S A 2006; 103:13962-7. [PMID: 16968770 PMCID: PMC1599896 DOI: 10.1073/pnas.0606384103] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.3] [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: 03/13/2006] [Indexed: 11/18/2022] Open
Abstract
Translational initiation factor 2 (IF2) is a guanine nucleotide-binding protein that can bind guanosine 3',5'-(bis) diphosphate (ppGpp), an alarmone involved in stringent response in bacteria. In cells growing under optimal conditions, the GTP concentration is very high, and that of ppGpp very low. However, under stress conditions, the GTP concentration may decline by as much as 50%, and that of ppGpp can attain levels comparable to those of GTP. Here we show that IF2 binds ppGpp at the same nucleotide-binding site and with similar affinity as GTP. Thus, GTP and the alarmone ppGpp can be considered two alternative physiologically relevant IF2 ligands. ppGpp interferes with IF2-dependent initiation complex formation, severely inhibits initiation dipeptide formation, and blocks the initiation step of translation. Our data suggest that IF2 has the properties of a cellular metabolic sensor and regulator that oscillates between an active GTP-bound form under conditions allowing active protein syntheses and an inactive ppGpp-bound form when shortage of nutrients would be detrimental, if not accompanied by slackening of this synthesis.
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Affiliation(s)
- Pohl Milon
- *Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
- Institute of Physical Biochemistry, University of Witten/Herdecke, 58448 Witten, Germany
| | - Eugene Tischenko
- Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, The Netherlands
| | - Jerneja Tomšic
- *Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
- Institute of Biochemistry, Polytechnic University of “The Marche,” 60131 Ancona, Italy; and
| | - Enrico Caserta
- *Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
- Institute of Biochemistry, Polytechnic University of “The Marche,” 60131 Ancona, Italy; and
| | - Gert Folkers
- Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, The Netherlands
| | - Anna La Teana
- Institute of Biochemistry, Polytechnic University of “The Marche,” 60131 Ancona, Italy; and
| | - Marina V. Rodnina
- Institute of Physical Biochemistry, University of Witten/Herdecke, 58448 Witten, Germany
| | - Cynthia L. Pon
- *Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
| | - Rolf Boelens
- Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH, Utrecht, The Netherlands
| | - Claudio O. Gualerzi
- *Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
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27
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Caserta E, Tomsic J, Spurio R, La Teana A, Pon CL, Gualerzi CO. Translation initiation factor IF2 interacts with the 30 S ribosomal subunit via two separate binding sites. J Mol Biol 2006; 362:787-99. [PMID: 16935296 DOI: 10.1016/j.jmb.2006.07.043] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [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: 05/19/2006] [Revised: 07/15/2006] [Accepted: 07/20/2006] [Indexed: 10/24/2022]
Abstract
The functional properties of the two natural forms of Escherichia coli translation initiation factor IF2 (IF2alpha and IF2beta) and of an N-terminal deletion mutant of the factor (IF2DeltaN) lacking the first 294 residues, corresponding to the entire N-terminal domain, were analysed comparatively. The results revealed that IF2alpha and IF2beta display almost indistinguishable properties, whereas IF2DeltaN, although fully active in all steps of the translation initiation pathway, displays functional activities having properties and requirements distinctly different from those of the intact molecule. Indeed, binding of IF2DeltaN to the 30 S subunit, IF2DeltaN-dependent stimulation of fMet-tRNA binding to the ribosome and of initiation dipeptide formation strongly depend upon the presence of IF1 and GTP, unlike with IF2alpha and IF2beta. The present results indicate that, using two separate active sites, IF2 establishes two interactions with the 30 S ribosomal subunit which have different properties and functions. The first site, located in the N domain of IF2, is responsible for a high-affinity interaction which "anchors" the factor to the subunit while the second site, mainly located in the beta-barrel module homologous to domain II of EF-G and EF-Tu, is responsible for the functional ("core") interaction of IF2 leading to the decoding of fMet-tRNA in the 30 S subunit P-site. The first interaction is functionally dispensable, sensitive to ionic-strength variations and essentially insensitive to the nature of the guanosine nucleotide ligand and to the presence of IF1, unlike the second interaction which strongly depends upon the presence of IF1 and GTP.
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Affiliation(s)
- Enrico Caserta
- Laboratory of Genetics, Department of Biology, University of Camerino, 62032 Camerino (MC), Italy
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28
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Allen GS, Zavialov A, Gursky R, Ehrenberg M, Frank J. The Cryo-EM Structure of a Translation Initiation Complex from Escherichia coli. Cell 2005; 121:703-12. [PMID: 15935757 DOI: 10.1016/j.cell.2005.03.023] [Citation(s) in RCA: 242] [Impact Index Per Article: 12.7] [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: 12/21/2004] [Revised: 03/14/2005] [Accepted: 03/22/2005] [Indexed: 11/22/2022]
Abstract
The 70S ribosome and its complement of factors required for initiation of translation in E. coli were purified separately and reassembled in vitro with GDPNP, producing a stable initiation complex (IC) stalled after 70S assembly. We have obtained a cryo-EM reconstruction of the IC showing IF2*GDPNP at the intersubunit cleft of the 70S ribosome. IF2*GDPNP contacts the 30S and 50S subunits as well as fMet-tRNA(fMet). IF2 here adopts a conformation radically different from that seen in the recent crystal structure of IF2. The C-terminal domain of IF2 binds to the single-stranded portion of fMet-tRNA(fMet), thereby forcing the tRNA into a novel orientation at the P site. The GTP binding domain of IF2 binds to the GTPase-associated center of the 50S subunit in a manner similar to EF-G and EF-Tu. Additionally, we present evidence for the localization of IF1, IF3, one C-terminal domain of L7/L12, and the N-terminal domain of IF2 in the initiation complex.
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Affiliation(s)
- Gregory S Allen
- Howard Hughes Medical Institute, Health Research, Inc. at the Wadsworth Center, Albany, New York 12201, USA
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29
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Spencer AC, Spremulli LL. The interaction of mitochondrial translational initiation factor 2 with the small ribosomal subunit. Biochim Biophys Acta 2005; 1750:69-81. [PMID: 15935986 DOI: 10.1016/j.bbapap.2005.03.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 03/03/2005] [Accepted: 03/07/2005] [Indexed: 10/25/2022]
Abstract
Bovine mitochondrial translational initiation factor 2 (IF-2(mt)) is organized into four domains, an N-terminal domain, a central G-domain and two C-terminal domains. These domains correspond to domains III-VI in the six-domain model of Escherichia coli IF-2. Variants in IF-2(mt) were prepared and tested for their abilities to bind the small (28S) subunit of the mitochondrial ribosome. The binding of wild-type IF-2(mt) was strong (K(d) approximately 10-20 nM) and was not affected by fMet-tRNA. Deletion of the N-terminal domain substantially reduced the binding of IF-2(mt) to 28S subunits. However, the addition of fMet-tRNA stimulated the binding of this variant at least 2-fold demonstrating that contacts between fMet-tRNA and IF-2(mt) can stabilize the binding of this factor to 28S subunits. No binding was observed for IF-2(mt) variants lacking the G-domain which probably plays a critical role in organizing the structure of IF-2(mt). IF-2(mt) contains a 37-amino acid insertion region between domains V and VI that is not found in the prokaryotic factors. Mutations in this region caused a significant reduction in the ability of the factor to promote initiation complex formation and to bind 28S subunits.
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Affiliation(s)
- Angela C Spencer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
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30
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Charrière F, Tan THP, Schneider A. Mitochondrial initiation factor 2 of Trypanosoma brucei binds imported formylated elongator-type tRNA(Met). J Biol Chem 2005; 280:15659-65. [PMID: 15731104 DOI: 10.1074/jbc.m411581200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [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 mitochondrion of Trypanosoma brucei lacks tRNA genes. Its translation system therefore depends on the import of nucleus-encoded tRNAs. Thus, except for the cytosol-specific initiator tRNA(Met), all trypanosomal tRNAs function in both the cytosol and the mitochondrion. The only tRNA(Met) present in T. brucei mitochondria is therefore the one which, in the cytosol, is involved in translation elongation. Mitochondrial translation initiation depends on an initiator tRNA(Met) carrying a formylated methionine. This tRNA is then recognized by initiation factor 2, which brings it to the ribosome. To guarantee mitochondrial translation initiation, T. brucei has an unusual methionyl-tRNA formyltransferase that formylates elongator tRNA(Met). In the present study, we have identified initiation factor 2 of T. brucei and shown that its carboxyl-terminal domain specifically binds formylated trypanosomal elongator tRNA(Met). Furthermore, the protein also recognizes the structurally very different Escherichia coli initiator tRNA(Met), suggesting that the main determinant recognized is the formylated methionine. In vivo studies using stable RNA interference cell lines showed that knock-down of initiation factor 2, depending on which construct was used, causes slow growth or even growth arrest. Moreover, concomitantly with ablation of the protein, a loss of oxidative phosphorylation was observed. Finally, although ablation of the methionyl-tRNA formyltransferase on its own did not impair growth, a complete growth arrest was observed when it was combined with the initiation factor 2 RNA interference cell line showing the slow growth phenotype. Thus, these experiments illustrate the importance of mitochondrial translation initiation for growth of procyclic T. brucei.
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Affiliation(s)
- Fabien Charrière
- Department of Biology/Zoology, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg, Switzerland
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31
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Steiner-Mosonyi M, Creuzenet C, Keates RAB, Strub BR, Mangroo D. The Pseudomonas aeruginosa initiation factor IF-2 is responsible for formylation-independent protein initiation in P. aeruginosa. J Biol Chem 2004; 279:52262-9. [PMID: 15385567 DOI: 10.1074/jbc.m408086200] [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
Formylation of the initiator methionyl-tRNA (Met-tRNAfMet) was generally thought to be essential for initiation of protein synthesis in all eubacteria based on studies conducted primarily in Escherichia coli. However, this view of eubacterial protein initiation has changed because some bacteria have been demonstrated to have the capacity to initiate protein synthesis with the unformylated Met-tRNAfMet. Here we show that the Pseudomonas aeruginosa initiation factor IF-2 is required for formylation-independent protein initiation in P. aeruginosa, the first bacterium shown to have the ability to initiate protein synthesis with both the initiator formyl-methionyl-tRNA (fMet-tRNAfMet) and Met-tRNAfMet. The E. coli IF-2, which participates exclusively in formylation-dependent protein initiation in E. coli, was unable to facilitate utilization of Met-tRNAfMet in initiation in P. aeruginosa. However, the E. coli IF-2 was made to function in formylation-independent protein initiation in P. aeruginosa by decreasing the positive charge potential of the cleft that binds the amino end of the amino acid attached to the tRNA. Furthermore increasing the positive charge potential of this cleft in the P. aeruginosa IF-2 prevented the protein from participating in formylation-independent protein initiation. Thus, this is the first demonstration of a eubacterial IF-2 with an inherent capacity to facilitate utilization of Met-tRNAfMet in protein initiation, discounting the dogma that eubacterial IF-2 can only allow the use of fMet-tRNAfMet in protein initiation. Furthermore these findings give important clues to the basis for discriminating the initiator Met-tRNA by IF-2 and for the evolution of alternative mechanisms for discrimination.
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MESH Headings
- Amino Acid Sequence
- Bacterial Proteins/chemistry
- Bacterial Proteins/genetics
- Bacterial Proteins/metabolism
- Base Sequence
- DNA, Bacterial/genetics
- Escherichia coli/genetics
- Escherichia coli/metabolism
- Escherichia coli Proteins/chemistry
- Escherichia coli Proteins/genetics
- Escherichia coli Proteins/metabolism
- Genetic Complementation Test
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Peptide Chain Initiation, Translational
- Prokaryotic Initiation Factor-2/chemistry
- Prokaryotic Initiation Factor-2/genetics
- Prokaryotic Initiation Factor-2/metabolism
- Protein Structure, Tertiary
- Pseudomonas aeruginosa/genetics
- Pseudomonas aeruginosa/metabolism
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Transfer, Met/genetics
- RNA, Transfer, Met/metabolism
- Sequence Homology, Amino Acid
- Static Electricity
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Affiliation(s)
- Marta Steiner-Mosonyi
- Department of Molecular and Cellular Biology, University of Guelph, Ontario N1G 2W1, Canada
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32
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Laursen BS, Kjaergaard AC, Mortensen KK, Hoffman DW, Sperling-Petersen HU. The N-terminal domain (IF2N) of bacterial translation initiation factor IF2 is connected to the conserved C-terminal domains by a flexible linker. Protein Sci 2004; 13:230-9. [PMID: 14691238 PMCID: PMC2286522 DOI: 10.1110/ps.03337604] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [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: 10/26/2022]
Abstract
Bacterial translation initiation factor IF2 is a multidomain protein that is an essential component of a system for ensuring that protein synthesis begins at the correct codon within a messenger RNA. Full-length IF2 from Escherichia coli and seven fragments of the protein were expressed, purified, and characterized using nuclear magnetic resonance (NMR) and circular dichroism (CD) methods. Interestingly, resonances of the 6 kD IF2N domain located at the extreme N terminus of IF2 can be clearly identified within the NMR spectra of the full-length 97-kD protein. (15)N NMR relaxation rate data indicate that (1) the IF2N domain is internally well ordered and tumbles in solution in a manner that is independent of the other domains of the IF2 protein, and (2) the IF2N domain is connected to the C-terminal regions of IF2 by a flexible linker. Chemical shifts of resonances within the isolated IF2N domain do not significantly differ from those of the corresponding residues within the context of the full-length 97-kD protein, indicating that IF2N is a structurally independent unit that does not strongly interact with other regions of IF2. CD and NMR data together provide evidence that Domains I-III of IF2 have unstructured and flexible regions as well as substantial helical content; CD data indicate that the helical content of these regions decreases significantly at temperatures above 35 degrees C. The features of structurally well-ordered N- and C-terminal domains connected by a flexible linker with significant helical content are reminiscent of another translation initiation factor, IF3.
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33
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Sørensen HP, Sperling-Petersen HU, Mortensen KK. A favorable solubility partner for the recombinant expression of streptavidin. Protein Expr Purif 2004; 32:252-9. [PMID: 14965771 DOI: 10.1016/j.pep.2003.07.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [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: 06/12/2003] [Revised: 07/02/2003] [Indexed: 11/16/2022]
Abstract
Recombinant streptavidin is extremely difficult to express at high levels in the cytoplasm of Escherichia coli without the formation of inclusion bodies. Fusing a solubility enhancing partner to an aggregation prone protein is a widely used tool to circumvent inclusion body formation. Here, we use streptavidin as a target protein to test the properties of N-terminal fragments of translation initiation factor IF2 from E. coli as a solubility partner. Domain I (residue 1-158) of IF2 is superior to the well-established solubility partners maltose-binding protein (MBP) and NusA for soluble expression of active streptavidin. The number of active streptavidin molecules isolated by chromatography is increased threefold when domain I is used as solubility partner as compared to MBP or NusA. The relatively small size, high expressivity, and extreme solubility make domain I of IF2 an ideal partner for streptavidin and may also prevent other recombinant proteins such as ScFv antibodies from being expressed as insoluble aggregates in the cytoplasm of E. coli.
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Affiliation(s)
- Hans Peter Sørensen
- Laboratory of BioDesign, Department of Molecular Biology, Aarhus University, Gustav Wieds Vej 10 C, DK-8000 Aarhus C, Denmark
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34
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Brandi L, Marzi S, Fabbretti A, Fleischer C, Hill WE, Gualerzi CO, Stephen Lodmell J. The translation initiation functions of IF2: targets for thiostrepton inhibition. J Mol Biol 2004; 335:881-94. [PMID: 14698286 DOI: 10.1016/j.jmb.2003.10.067] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [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: 11/23/2022]
Abstract
Bacterial translation initiation factor IF2 was localized on the ribosome by rRNA cleavage using free Cu(II):1,10-orthophenanthroline. The results indicated proximity of IF2 to helix 89, to the sarcin-ricin loop and to helices 43 and 44, which constitute the "L11/thiostrepton" stem-loops of 23S rRNA. These findings prompted an investigation of the L11 contribution to IF2 activity and a re-examination of the controversial issue of the effect on IF2 functions of thiostrepton, a peptide antibiotic known primarily as a powerful inhibitor of translocation. Ribosomes lacking L11 were found to have wild-type capacity to bind IF2 but a strongly reduced ability to elicit its GTPase activity. We found that thiostrepton caused a faster recycling of this factor on and off the 70S ribosomes and 50S subunits, which in turn resulted in an increased rate of the multiple turnover IF2-dependent GTPase. Although thiostrepton did not inhibit the P-site binding of fMet-tRNA, the A-site binding of the EF-Tu-GTP-Phe-tRNA or the activity of the ribosomal peptidyl transferase center (as measured by the formation of fMet-puromycin), it severely inhibited IF2-dependent initiation dipeptide formation. This inhibition can probably be traced back to a thiostrepton-induced distortion of the ribosomal-binding site of IF2, which leads to a non-productive interaction between the ribosome and the aminoacyl-tRNA substrates of the peptidyl transferase reaction. Overall, our data indicate that the translation initiation function of IF2 is as sensitive as the translocation function of EF-G to thiostrepton inhibition.
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Affiliation(s)
- Letizia Brandi
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC), Italy
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35
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Marzi S, Knight W, Brandi L, Caserta E, Soboleva N, Hill WE, Gualerzi CO, Lodmell JS. Ribosomal localization of translation initiation factor IF2. RNA 2003; 9:958-69. [PMID: 12869707 PMCID: PMC1370462 DOI: 10.1261/rna.2116303] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [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: 08/09/2002] [Accepted: 05/15/2003] [Indexed: 05/22/2023]
Abstract
Bacterial translation initiation factor IF2 is a GTP-binding protein that catalyzes binding of initiator fMet-tRNA in the ribosomal P site. The topographical localization of IF2 on the ribosomal subunits, a prerequisite for understanding the mechanism of initiation complex formation, has remained elusive. Here, we present a model for the positioning of IF2 in the 70S initiation complex as determined by cleavage of rRNA by the chemical nucleases Cu(II):1,10-orthophenanthroline and Fe(II):EDTA tethered to cysteine residues introduced into IF2. Two specific amino acids in the GII domain of IF2 are in proximity to helices H3, H4, H17, and H18 of 16S rRNA. Furthermore, the junction of the C-1 and C-2 domains is in proximity to H89 and the thiostrepton region of 23S rRNA. The docking is further constrained by the requisite proximity of the C-2 domain with P-site-bound tRNA and by the conserved GI domain of the IF2 with the large subunit's factor-binding center. Comparison of our present findings with previous data further suggests that the IF2 orientation on the 30S subunit changes during the transition from the 30S to 70S initiation complex.
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Affiliation(s)
- Stefano Marzi
- Laboratory of Genetics, Department of Biology MCA, University of Camerino, 62032 Camerino (MC) Italy
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36
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Abstract
Rapid protein synthesis in bacteria requires the G proteins IF2, EF-Tu, EF-G, and RF3. These factors catalyze all major steps of mRNA translation in a GTP-dependent manner. Here, it is shown how the position of peptidyl-tRNA in the ribosome and presence of its peptide control the binding and GTPase activity of these translation factors. The results explain how idling GTPase activity and negative interference between different translation factors are avoided and suggest that hybrid sites for tRNA on the ribosome play essential roles in translocation of tRNAs, recycling of class 1 release factors by RF3, and recycling of ribosomes back to a new round of initiation. We also propose a model for translocation of tRNAs in two separate steps, which clarifies the roles of EF-G.GTP and GTP hydrolysis in this process.
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Affiliation(s)
- Andrey V Zavialov
- Department of Cell and Molecular Biology, BMC, Uppsala University, Box 596, S-75124 Uppsala, Sweden.
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37
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Dever TE, Roll-Mecak A, Choi SK, Lee JH, Cao C, Shin BS, Burley SK. Universal translation initiation factor IF2/eIF5B. Cold Spring Harb Symp Quant Biol 2003; 66:417-24. [PMID: 12762044 DOI: 10.1101/sqb.2001.66.417] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- T E Dever
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-2716, USA
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38
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Quevedo C, Salinas M, Alcázar A. Initiation factor 2B activity is regulated by protein phosphatase 1, which is activated by the mitogen-activated protein kinase-dependent pathway in insulin-like growth factor 1-stimulated neuronal cells. J Biol Chem 2003; 278:16579-86. [PMID: 12624094 DOI: 10.1074/jbc.m212936200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [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
We have previously demonstrated that insulin-like growth factor 1 (IGF1) induces eukaryotic initiation factor 2B (eIF2B) activation in neuronal cells through the phosphatidylinositol 3 kinase/glycogen synthase kinase 3 pathway as well as by activation of the mitogen-activated protein kinase (MAPK)-activating kinase (MEK)/MAPK signaling pathway (Quevedo, C., Alcázar, A., and Salinas, M. (2000) J. Biol. Chem. 275, 19192-19197). This paper addresses the mechanism involved in IGF1-induced eIF2B activation via the MEK/MAPK cascade in cultured neurons treated with IGF1 and demonstrates that extracellular signal-regulated MAP kinase 1 and 2 (ERK1 and -2) immunoprecipitates of IGF1-treated neuronal cells promote this activation. This effect did not directly result from eIF2B phosphorylation by ERK immunoprecipitates. In addition, recombinant ERK1 and -2 neither activate eIF2B nor phosphorylate it. Endogenous protein phosphatase 1 and 2A catalytic subunits (PP1C and PP2AC, respectively) were co-immunoprecipitated with ERK1 and -2, and the association of ERK with PP1C was stimulated by IGF1 treatment, resulting in increased PP1 activity. ERK immunoprecipitates incubated with PP1 inhibitors did not activate eIF2B, indicating that PP1C activates eIF2B. In vitro experiments with phosphorylated eIF2B showed that recombinant PP1C (alpha isoform) dephosphorylates and activates eIF2B. Paralleling eIF2B activation, IGF1 treatment induced PP1 activation in a MEK/MAPK-dependent fashion. Moreover, the treatment of neurons with the PP1 inhibitor tautomycin inhibited PP1 activation and prevented IGF1-induced eIF2B activation. These findings strongly suggest that IGF1-induced eIF2B activation in neurons is effected by PP1, the activation of which is mediated by the MEK/MAPK signaling pathway.
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Affiliation(s)
- Celia Quevedo
- Servicio de Bioquímica-Investigación, Hospital Ramón y Cajal, 28034 Madrid, Spain
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Evans JM, Turner BA, Bowen S, Ho AM, Sarver RW, Benson E, Parker CN. Inhibition of bacterial IF2 binding to fMet-tRNA((fMet)) by aminoglycosides. Bioorg Med Chem Lett 2003; 13:993-6. [PMID: 12643896 DOI: 10.1016/s0960-894x(03)00085-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [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: 11/16/2022]
Abstract
Screening for inhibitors of bacterial protein synthesis Initiation Factor 2 (IF2) binding to N-formyl-Methionyl-transfer RNA (fMet-tRNA((fMet))) identified a series of aminoglycosides, that included amikacin and kanamycin A1, as inhibitors of this interaction. Subsequent testing revealed that aminoglycosides displayed a wide range of inhibitory activity. However, the failure of these compounds to completely inhibit binding of IF2 to fMet-tRNA((fMet)), the known ability of aminoglycosides to bind RNA, and the ability of the aminoglycosides to displace PicoGreen bound to fMet-tRNA((fMet)) suggest these compounds act by binding fMet-tRNA((fMet)). This hypothesis is further supported by isothermal denaturation experiments that failed to show any interaction between the IF2 protein and the aminoglycosides.
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Affiliation(s)
- J M Evans
- Global High Throughput Screening, Pharmacia Corp., Kalamazoo, MI 49007, USA
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40
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Laursen BS, Siwanowicz I, Larigauderie G, Hedegaard J, Ito K, Nakamura Y, Kenney JM, Mortensen KK, Sperling-Petersen HU. Characterization of mutations in the GTP-binding domain of IF2 resulting in cold-sensitive growth of Escherichia coli. J Mol Biol 2003; 326:543-51. [PMID: 12559921 DOI: 10.1016/s0022-2836(02)01367-0] [Citation(s) in RCA: 18] [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: 11/17/2022]
Abstract
The infB gene encodes translation initiation factor IF2. We have determined the entire sequence of infB from two cold-sensitive Escherichia coli strains IQ489 and IQ490. These two strains have been isolated as suppressor strains for the temperature-sensitive secretion mutation secY24. The mutations causing the suppression phenotype are located within infB. The only variations from the wild-type (wt) infB found in the two mutant strains are a replacement of Asp409 with Glu in strain IQ489 and an insertion of Gly between Ala421 and Gly422 in strain IQ490. Both positions are located in the GTP-binding G-domain of IF2. A model of the G-domain of E.coli IF2 is presented in. Physiological quantities of the recombinant mutant proteins were expressed in vivo in E.coli strains from which the chromosomal infB gene has been inactivated. At 42 degrees C, the mutants sustained normal cell growth, whereas a significant decrease in growth rate was found at 25 degrees C for both mutants as compared to wt IF2 expressed in the control strain. Circular dichroism spectra were recorded of the wt and the two mutant proteins to investigate the structural properties of the proteins. The spectra are characteristic of alpha-helix dominated structure, and reveal a significant different behavior between the wt and mutant IF2s with respect to temperature-induced conformational changes. The temperature-induced conformational change of the wt IF2 is a two-state process. In a ribosome-dependent GTPase assay in vitro the two mutants showed practically no activity at temperatures below 10 degrees C and a reduced activity at all temperatures up to 45 degrees C, as compared to wt IF2. The results indicate that the amino acid residues, Asp409 and Gly422, are located in important regions of the IF2 G-domain and demonstrate the importance of GTP hydrolysis in translation initiation for optimal cell growth.
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Shin BS, Maag D, Roll-Mecak A, Arefin MS, Burley SK, Lorsch JR, Dever TE. Uncoupling of initiation factor eIF5B/IF2 GTPase and translational activities by mutations that lower ribosome affinity. Cell 2002; 111:1015-25. [PMID: 12507428 DOI: 10.1016/s0092-8674(02)01171-6] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [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]
Abstract
Translation initiation factor eIF5B/IF2 is a GTPase that promotes ribosomal subunit joining. We show that eIF5B mutations in Switch I, an element conserved in all GTP binding domains, impair GTP hydrolysis and general translation but not eIF5B subunit joining function. Intragenic suppressors of the Switch I mutation restore general translation, but not eIF5B GTPase activity. These suppressor mutations reduce the ribosome affinity of eIF5B and increase AUG skipping/leaky scanning. The uncoupling of translation and eIF5B GTPase activity suggests a regulatory rather than mechanical function for eIF5B GTP hydrolysis in translation initiation. The translational defect suggests eIF5B stabilizes Met-tRNA(i)(Met) binding and that GTP hydrolysis by eIF5B is a checkpoint monitoring 80S ribosome assembly in the final step of translation initiation.
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Affiliation(s)
- Byung-Sik Shin
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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