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Abstract
Fluoride is ubiquitously present throughout the world. It is released from minerals, magmatic gas, and industrial processing, and travels in the atmosphere and water. Exposure to low concentrations of fluoride increases overall oral health. Consequently, many countries add fluoride to their public water supply at 0.7-1.5 ppm. Exposure to high concentrations of fluoride, such as in a laboratory setting often exceeding 100 ppm, results in a wide array of toxicity phenotypes. This includes oxidative stress, organelle damage, and apoptosis in single cells, and skeletal and soft tissue damage in multicellular organisms. The mechanism of fluoride toxicity can be broadly attributed to four mechanisms: inhibition of proteins, organelle disruption, altered pH, and electrolyte imbalance. Recently, there has been renewed concern in the public sector as to whether fluoride is safe at the current exposure levels. In this review, we will focus on the impact of fluoride at the chemical, cellular, and multisystem level, as well as how organisms defend against fluoride. We also address public concerns about fluoride toxicity, including whether fluoride has a significant effect on neurodegeneration, diabetes, and the endocrine system.
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Affiliation(s)
- Nichole R Johnston
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Scott A Strobel
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA.
- Department of Chemistry, Yale University, New Haven, CT, 06520, USA.
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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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Dionne CA, Stearns GB, Kramer G, Hardesty B. Inhibition of peptide initiation by a low molecular weight RNA from rabbit reticulocytes. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)33723-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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FLoyd GA, Traugh JA. Effects of cyclic AMP and fluoride on phosphorylation of ribosomal protein S6 and on protein synthesis in rabbit reticulocytes. Eur J Biochem 1981; 117:257-62. [PMID: 6168467 DOI: 10.1111/j.1432-1033.1981.tb06331.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The effects of N6,O2-dibutyryl-adenosine 3',5'-monophosphate (Bt2cAMP) and sodium fluoride on the phosphorylation of ribosomal proteins S6 and on protein synthesis were examined. Rabbit reticulocytes were incubated in a nutritional medium containing 32Pi in the presence and absence of Bt2cAMP (1mM) and 3-isobutyl-1-methyl-xanthine (1mM). In the control cells, four phosphorylated derivatives of S6 were observed, with most of the radioactivity in the monophosphorylated form. Upon addition of cyclic nucleotide, a twofold increase in the phosphorylation of ribosomal protein S6 was observed. This was accompanied by an increase of radioactive phosphate in the diphosphorylated derivative. No alteration in protein synthesis was observed upon addition of cAMP and analogues of cAMP in conjunction with 3-isobutyl-1-methyl-xanthine or theophylline. The effects of sodium fluoride on phosphorylation of S6 and on protein synthesis were examined also. At 5 mM sodium fluoride, protein synthesis was inhibited by 85%. A 2.5-fold increase in the phosphorylation of ribosomal protein S6 was observed with an accumulation of 32Pi in the diphosphorylated, triphosphorylated and tetraphosphorylated derivatives. Inhibition of protein synthesis coincided with an increase in the more highly phosphorylated derivatives, whereas an increase of radioactive phosphate in the diphosphorylated derivative could not be correlated with an alteration in globin synthesis.
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Odon O, Kramer G, Henderson A, Pinphanichakarn P, Hardesty B. GTP hydrolysis during methionyl-tRNAf binding to 40 S ribosomal subunits and the site of edeine inhibition. J Biol Chem 1978. [DOI: 10.1016/s0021-9258(19)62324-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Safer B, Anderson WF. The molecular mechanism of hemoglobin synthesis and its regulation in the reticulocyte. CRC Crit Rev Biochem 1978; 5:261-90. [PMID: 363353 DOI: 10.3109/10409237809177144] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Pinphanichakarn P, Kramer G, Hardesty B. Partial purification and characterization of a translational inhibitor from Friend leukemia cells. J Biol Chem 1977. [DOI: 10.1016/s0021-9258(18)71872-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Nygård O, Hultin T. Accumulation of tRNAMetf on 80-S ribosomes in vitro under the influence of a Met-tRNA deacylase from rat-liver microsomes. Eur J Biochem 1977; 72:537-42. [PMID: 837928 DOI: 10.1111/j.1432-1033.1977.tb11277.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A Met-tRNA deacylase has been partially purified from the 0.5 M KCl wash of rat liver microsomes. In preparative sucrose gradients, the active component sediments as a single band at about 6 S, corresponding to an estimated molecular weight of 1.7 X 10(5). The deacylase is specific for Met-tRNA, without discriminating between Met-tRNA f and Met-tRNAm. Met-tRNAf bound to the initiation factor IF-MP in the ternary complex, IF-MP-GTP-Met-tRNAf, or to initiation-factor-dependent, complexes with 40-S subunits or 80-S ribosomes, is protected against deacylation. However, in the course of the initiation-factor-dependent joining of the 40-S subunit complex to 60-S ribosomal subunits, the bound Met-tRNAf is exposed to added deacylase. Under these conditions, deacylation is inhibited by GTP. The tRNAMetf remains bound and accumulates on the 80-S ribosomes.
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Pinphanichakarn P, Kramer G, Hardesty B. Partial reaction of peptide initiation inhibited by the reticulocyte hemin-controlled repressor. Biochem Biophys Res Commun 1976; 73:625-31. [PMID: 1008879 DOI: 10.1016/0006-291x(76)90856-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Smith DWE. Response
: Reticulocyte Transfer RNA and Hemoglobin Synthesis. Science 1976. [DOI: 10.1126/science.193.4251.429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- David W. E. Smith
- Department of Pathology,
Northwestern University Medical
School, Chicago, Illinois 60611
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Godchaux W, Atwood KC. Structure and function of initiation complexes which accumulate during inhibition of protein synthesis by fluoride ion. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(17)33877-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Abstract
A peptide initiation factor purified from rat liver and promoting the binding of initiator tRNA and model initiators to 40S and 80S ribosome at an acid pH liberates methionine and N-acetylmethionine from Trna Met f at neutral reaction. Phenylalanyl-tRNA, N-acetylphenylalanyl-tRNA and methionyl-tRNA Met m are not hydrolyzed under the same conditions. Hydrolysis of methionyl-tRNA Met f is stimulated by the presence of the 40S ribosomal subunit and preceeds at 37 degrees C until all the substrate has been split. No hydrolysis of initiator tRNA or N-acetylmethionyl-tRNA Met f occurs at 0 degrees C. Hydrolysis is slightly stimulated by GTP and MG2+ but not by KCl. The binding and hydrolyzing activity associated with a single protein factor may have an important function in regulating the rate of peptide initiation.
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Cimadevilla JM, Hardesty B. Isolation and partial characterization of a 40 S ribosomal subunit-transfer ribonucleic acid binding factor from rabbit reticulocytes. J Biol Chem 1975. [DOI: 10.1016/s0021-9258(19)41314-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Cimadevilla JM, Hardesty B. Aminoacyl-tRNA specificity of a 40S ribosomal subunit binding factor from rabbit reticulocytes. Biochem Biophys Res Commun 1975; 63:16-23. [PMID: 1125008 DOI: 10.1016/s0006-291x(75)80004-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Cimadevilla JM, Morrisey J, Hardesty B. A functional interaction between methionyl-transfer RNA hydrolase and a transfer RNA binding factor. J Mol Biol 1974; 83:437-46. [PMID: 4830855 DOI: 10.1016/0022-2836(74)90505-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Morrisey J, Hardesty B. Assay and purification of Met-tRNA hydrolase from rabbit reticulocytes. Methods Enzymol 1974; 29:726-39. [PMID: 4850661 DOI: 10.1016/0076-6879(74)29065-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Katze JR, Mason KH. Comparison of the acceptance activity of the ribosome-bound and the total cellular transfer ribonucleic acids from SV40-transformed mouse fibroblasts. Biochim Biophys Acta 1973; 331:369-81. [PMID: 4360078 DOI: 10.1016/0005-2787(73)90023-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Hardesty B, Obrig T, Irvin J, Culp W. The effect of sodium fluoride, edeine, and cycloheximide on peptide synthesis with reticulocyte ribosomes. Basic Life Sci 1973; 1:377-92. [PMID: 4773153 DOI: 10.1007/978-1-4684-0877-5_30] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Lundquist RE, Lazar JM, Klein WH, Clark JM. Translation of satellite tobacco necrosis virus ribonucleic acid. II. Initiation of in vitro translation in procaryotic and eucaryotic systems. Biochemistry 1972; 11:2014-9. [PMID: 4337485 DOI: 10.1021/bi00761a004] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Stewart JW, Sherman F, Shipman NA, Jackson M. Identification and Mutational Relocation of the AUG Codon Initiating Translation of Iso-1-Cytochrome c in Yeast. J Biol Chem 1971. [DOI: 10.1016/s0021-9258(19)45798-0] [Citation(s) in RCA: 93] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Stewart-Blair ML, Yanowitz IS, Goldberg IH. Inhibition of synthesis of new globin chains in reticulocyte lysates by pactamycin. Biochemistry 1971; 10:4198-206. [PMID: 5126935 DOI: 10.1021/bi00799a007] [Citation(s) in RCA: 46] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Shafritz DA, Laycock DG, Crystal RG, Anderson WF. Requirement for GTP in the initiation process on reticulocyte ribosomes and ribosomal subunits. Proc Natl Acad Sci U S A 1971; 68:2246-51. [PMID: 5289383 PMCID: PMC389394 DOI: 10.1073/pnas.68.9.2246] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The requirement for GTP in the initiation process on reticulocyte ribosomes and ribosomal subunits has been examined by studying Met-tRNA(F) binding, ribosome-dependent [gamma-(32)P]GTP hydrolysis, and peptide-bond formation with puromycin. Met-tRNA(F) binding can be obtained with the methylene analogue, 5'-guanylylmethylene diphosphonate, as well as GTP, and it is not inhibited by fusidic acid or several other inhibitors of protein synthesis. This reaction can be performed with the 40S subunit and has the same requirements as the Met-tRNA(F)-binding reaction with washed ribosomes. Ribosome-dependent [gamma-(32)P]GTP hydrolysis can be obtained with the initiation factor M(2A) using either washed ribosomes or the 40S subunit. This reaction is also not significantly inhibited by fusidic acid. Peptide-bond formation between puromycin and Met-tRNA(F), however, is inhibited by fusidic acid, and does not occur if the methylene analogue of GTP is substituted for GTP. These data suggest that the binding of the initiator tRNA to the 40S subunit does not require the hydrolysis of GTP, but that at least one GTP hydrolysis event must occur after Met-tRNA(F) binding in order for the first peptide bond to be formed.
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Abstract
Initiation factors M(1) + M(2) from reticulocyte ribosomes bind Met-tRNA(F) to rabbit reticulocyte ribosomes containing endogenous hemoglobin mRNA. The initial binding of Met-tRNA(F) appears to be to the small ribosomal subunit. The Met-tRNA(F) is able to participate in what is presumed to be the first peptide bond in the formation of hemoglobin, namely the synthesis of a methionyl-valine dipeptide. The formation of this methionyl-valine dipeptide requires Met-tRNA(F), initiation factors M(1), M(2), and M(3), as well as Val-tRNA and T(1). No synthesis of methionyl-valine dipeptide takes place if Met-tRNA(F) is replaced by Met-tRNA(M), or if initiation factor M(3) is omitted. Thus, Met-tRNA(F) appears to be the initiator tRNA for hemoglobin biosynthesis and M(3), although required for the synthesis of the first peptide bond of hemoglobin, does not appear to be necessary, under the experimental conditions studied, for Met-tRNA(F) binding.
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Pawelek J, Godchaux W, Grasso J, Skoultchi AI, Eisenstadt J, Lengyel P. Occurrence of cysteinyl transfer ribonucleic acid with a blocked alpha-amino group in rabbit reticulocytes. Biochim Biophys Acta 1971; 232:289-305. [PMID: 4928711 DOI: 10.1016/0005-2787(71)90582-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Shafritz DA, Laycock DG, Anderson WF. Puromycin-peptide bond formation with reticulocyte initiation factors M1 and M2. Proc Natl Acad Sci U S A 1971; 68:496-9. [PMID: 5277107 PMCID: PMC388968 DOI: 10.1073/pnas.68.2.496] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The ability to form a "peptide" bond between various forms of Met-tRNA or Phe-tRNA and puromycin has been studied in the reticulocyte cell-free system. When Met-tRNA(F), fMet-tRNA(F), or N-acetylPhe-tRNA are used as substrate at low Mg(++) concentration (3 mM), reticulocyte initiation factors M(1) and M(2) (M(2A) + M(2B)) are required for puromycin-peptide synthesis. In contrast to bacterial systems, this reaction is also stimulated by the elongation factor T(1). When Met-tRNA(M) or Phe-tRNA is used as substrate, there is no M-factor requirement for the puromycin reaction; T(1) is absolutely required, and the reaction is stimulated by T(2). These studies indicate that reticulocyte factors M(1) and M(2) may function in part by placing the initiator tRNA into the P site. The detailed mechanism for mammalian initiation, however, may be more complex than that for bacterial systems.
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Obrig TG, Culp WJ, Mckeehan WL, Hardesty B. The Mechanism by which Cycloheximide and Related Glutarimide Antibiotics Inhibit Peptide Synthesis on Reticulocyte Ribosomes. J Biol Chem 1971; 246:174-81. [DOI: 10.1016/s0021-9258(18)62546-3] [Citation(s) in RCA: 355] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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