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Manta B, Makarova NE, Mariotti M. The selenophosphate synthetase family: A review. Free Radic Biol Med 2022; 192:63-76. [PMID: 36122644 DOI: 10.1016/j.freeradbiomed.2022.09.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 09/11/2022] [Accepted: 09/12/2022] [Indexed: 11/23/2022]
Abstract
Selenophosphate synthetases use selenium and ATP to synthesize selenophosphate. This is required for biological utilization of selenium, most notably for the synthesis of the non-canonical amino acid selenocysteine (Sec). Therefore, selenophosphate synthetases underlie all functions of selenoproteins, which include redox homeostasis, protein quality control, hormone regulation, metabolism, and many others. This protein family comprises two groups, SelD/SPS2 and SPS1. The SelD/SPS2 group represent true selenophosphate synthetases, enzymes central to selenium metabolism which are present in all Sec-utilizing organisms across the tree of life. Notably, many SelD/SPS2 proteins contain Sec as catalytic residue in their N-terminal flexible selenium-binding loop, while others replace it with cysteine (Cys). The SPS1 group comprises proteins originated through gene duplications of SelD/SPS2 in metazoa in which the Sec/Cys-dependent catalysis was disrupted. SPS1 proteins do not synthesize selenophosphate and are not required for Sec synthesis. They have essential regulatory functions related to redox homeostasis and pyridoxal phosphate, which affect signaling pathways for growth and differentiation. In this review, we summarize the knowledge about the selenophosphate synthetase family acquired through decades of research, encompassing their structure, mechanism, function, and evolution.
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Affiliation(s)
- Bruno Manta
- Laboratorio de Genómica Microbiana, Institut Pasteur Montevideo, Uruguay, Cátedra de Fisiopatología, Facultad de Odontología, Universidad de la República, Uruguay
| | - Nadezhda E Makarova
- Departament de Genètica, Microbiologia i Estadística, Facultat de Biologia, Universitat de Barcelona (UB), Avinguda Diagonal 643, Barcelona, 08028, Catalonia, Spain
| | - Marco Mariotti
- Departament de Genètica, Microbiologia i Estadística, Facultat de Biologia, Universitat de Barcelona (UB), Avinguda Diagonal 643, Barcelona, 08028, Catalonia, Spain.
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2
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Shetty SP, Kiledjian NT, Copeland PR. The selenoprotein P 3' untranslated region is an RNA binding protein platform that fine tunes selenocysteine incorporation. PLoS One 2022; 17:e0271453. [PMID: 35905095 PMCID: PMC9337670 DOI: 10.1371/journal.pone.0271453] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 07/01/2022] [Indexed: 11/19/2022] Open
Abstract
Selenoproteins contain the 21st amino acid, selenocysteine (Sec), which is incorporated at select UGA codons when a specialized hairpin sequence, the Sec insertion sequence (SECIS) element, is present in the 3' UTR. Aside from the SECIS, selenoprotein mRNA 3' UTRs are not conserved between different selenoproteins within a species. In contrast, the 3'-UTR of a given selenoprotein is often conserved across species, which supports the hypothesis that cis-acting elements in the 3'-UTR other than the SECIS exert post-transcriptional control on selenoprotein expression. In order to determine the function of one such SECIS context, we chose to focus on the plasma selenoprotein, SELENOP, which is required to maintain selenium homeostasis as a selenium transport protein that contains 10 Sec residues. It is unique in that its mRNA contains two SECIS elements in the context of a highly conserved 843-nucleotide 3' UTR. Here we have used RNA affinity chromatography and identified PTBP1 as the major RNA binding protein that specifically interacts with the sequence between the two SECIS elements. We then used CRISPR/Cas9 genome editing to delete two regions surrounding the first SECIS element. We found that these sequences are involved in regulating SELENOP mRNA and protein levels, which are inversely altered as a function of selenium concentrations.
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Affiliation(s)
- Sumangala P. Shetty
- Department of Biochemistry and Molecular Biology, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ, United States of America
| | - Nora T. Kiledjian
- Department of Biochemistry and Molecular Biology, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ, United States of America
| | - Paul R. Copeland
- Department of Biochemistry and Molecular Biology, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ, United States of America
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3
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Noda Y, Okada S, Suzuki T. Regulation of A-to-I RNA editing and stop codon recoding to control selenoprotein expression during skeletal myogenesis. Nat Commun 2022; 13:2503. [PMID: 35523818 PMCID: PMC9076623 DOI: 10.1038/s41467-022-30181-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2021] [Accepted: 04/05/2022] [Indexed: 12/13/2022] Open
Abstract
Selenoprotein N (SELENON), a selenocysteine (Sec)-containing protein with high reductive activity, maintains redox homeostasis, thereby contributing to skeletal muscle differentiation and function. Loss-of-function mutations in SELENON cause severe neuromuscular disorders. In the early-to-middle stage of myoblast differentiation, SELENON maintains redox homeostasis and modulates endoplasmic reticulum (ER) Ca2+ concentration, resulting in a gradual reduction from the middle-to-late stages due to unknown mechanisms. The present study describes post-transcriptional mechanisms that regulate SELENON expression during myoblast differentiation. Part of an Alu element in the second intron of SELENON pre-mRNA is frequently exonized during splicing, resulting in an aberrant mRNA that is degraded by nonsense-mediated mRNA decay (NMD). In the middle stage of myoblast differentiation, ADAR1-mediated A-to-I RNA editing occurs in the U1 snRNA binding site at 5' splice site, preventing Alu exonization and producing mature mRNA. In the middle-to-late stage of myoblast differentiation, the level of Sec-charged tRNASec decreases due to downregulation of essential recoding factors for Sec insertion, thereby generating a premature termination codon in SELENON mRNA, which is targeted by NMD.
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Affiliation(s)
- Yuta Noda
- Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
| | - Shunpei Okada
- Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
- Department of Microbiology, Faculty of Medicine, Shimane University, 89-1 Enyacho, Izumo, Shimane, 693-8501, Japan
| | - Tsutomu Suzuki
- Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
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Copeland PR, Howard MT. Ribosome Fate during Decoding of UGA-Sec Codons. Int J Mol Sci 2021; 22:ijms222413204. [PMID: 34948001 PMCID: PMC8704476 DOI: 10.3390/ijms222413204] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 11/29/2021] [Accepted: 12/06/2021] [Indexed: 12/14/2022] Open
Abstract
Decoding of genetic information into polypeptides occurs during translation, generally following the codon assignment rules of the organism's genetic code. However, recoding signals in certain mRNAs can overwrite the normal rules of translation. An exquisite example of this occurs during translation of selenoprotein mRNAs, wherein UGA codons are reassigned to encode for the 21st proteogenic amino acid, selenocysteine. In this review, we will examine what is known about the mechanisms of UGA recoding and discuss the fate of ribosomes that fail to incorporate selenocysteine.
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Affiliation(s)
- Paul R. Copeland
- Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
- Correspondence: (P.R.C.); (M.T.H.)
| | - Michael T. Howard
- Department of Human Genetics, University of Utah, Salt Lake City, UT 84112, USA
- Correspondence: (P.R.C.); (M.T.H.)
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5
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Natural Autoimmunity to Selenoprotein P Impairs Selenium Transport in Hashimoto's Thyroiditis. Int J Mol Sci 2021; 22:ijms222313088. [PMID: 34884891 PMCID: PMC8658221 DOI: 10.3390/ijms222313088] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 11/26/2021] [Accepted: 11/30/2021] [Indexed: 02/07/2023] Open
Abstract
The essential trace element selenium (Se) is needed for the biosynthesis of selenocysteine-containing selenoproteins, including the secreted enzyme glutathione peroxidase 3 (GPX3) and the Se-transporter selenoprotein P (SELENOP). Both are found in blood and thyroid colloid, where they serve protective functions. Serum SELENOP derives mainly from hepatocytes, whereas the kidney contributes most serum GPX3. Studies using transgenic mice indicated that renal GPX3 biosynthesis depends on Se supply by hepatic SELENOP, which is produced in protein variants with varying Se contents. Low Se status is an established risk factor for autoimmune thyroid disease, and thyroid autoimmunity generates novel autoantigens. We hypothesized that natural autoantibodies to SELENOP are prevalent in thyroid patients, impair Se transport, and negatively affect GPX3 biosynthesis. Using a newly established quantitative immunoassay, SELENOP autoantibodies were particularly prevalent in Hashimoto’s thyroiditis as compared with healthy control subjects (6.6% versus 0.3%). Serum samples rich in SELENOP autoantibodies displayed relatively high total Se and SELENOP concentrations in comparison with autoantibody-negative samples ([Se]; 85.3 vs. 77.1 µg/L, p = 0.0178, and [SELENOP]; 5.1 vs. 3.5 mg/L, p = 0.001), while GPX3 activity was low and correlated inversely to SELENOP autoantibody concentrations. In renal cells in culture, antibodies to SELENOP inhibited Se uptake. Our results indicate an impairment of SELENOP-dependent Se transport by natural SELENOP autoantibodies, suggesting that the characterization of health risk from Se deficiency may need to include autoimmunity to SELENOP as additional biomarker of Se status.
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Choudhary S, Li W, D Smith A. Accurate detection of short and long active ORFs using Ribo-seq data. Bioinformatics 2020; 36:2053-2059. [PMID: 31750902 DOI: 10.1093/bioinformatics/btz878] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 11/04/2019] [Accepted: 11/20/2019] [Indexed: 12/27/2022] Open
Abstract
MOTIVATION Ribo-seq, a technique for deep-sequencing ribosome-protected mRNA fragments, has enabled transcriptome-wide monitoring of translation in vivo. It has opened avenues for re-evaluating the coding potential of open reading frames (ORFs), including many short ORFs that were previously presumed to be non-translating. However, the detection of translating ORFs, specifically short ORFs, from Ribo-seq data, remains challenging due to its high heterogeneity and noise. RESULTS We present ribotricer, a method for detecting actively translating ORFs by directly leveraging the three-nucleotide periodicity of Ribo-seq data. Ribotricer demonstrates higher accuracy and robustness compared with other methods at detecting actively translating ORFs including short ORFs on multiple published datasets across species inclusive of Arabidopsis, Caenorhabditis elegans, Drosophila, human, mouse, rat, yeast and zebrafish. AVAILABILITY AND IMPLEMENTATION Ribotricer is available at https://github.com/smithlabcode/ribotricer. All analysis scripts and results are available at https://github.com/smithlabcode/ribotricer-results. SUPPLEMENTARY INFORMATION Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- Saket Choudhary
- Computational Biology and Bioinformatics, University of Southern California, Los Angeles, CA 90089, USA
| | - Wenzheng Li
- Computational Biology and Bioinformatics, University of Southern California, Los Angeles, CA 90089, USA
| | - Andrew D Smith
- Computational Biology and Bioinformatics, University of Southern California, Los Angeles, CA 90089, USA
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Santesmasses D, Mariotti M, Gladyshev VN. Bioinformatics of Selenoproteins. Antioxid Redox Signal 2020; 33:525-536. [PMID: 32031018 PMCID: PMC7409585 DOI: 10.1089/ars.2020.8044] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Accepted: 02/05/2020] [Indexed: 12/13/2022]
Abstract
Significance: Bioinformatics has brought important insights into the field of selenium research. The progress made in the development of computational tools in the last two decades, coordinated with growing genome resources, provided new opportunities to study selenoproteins. The present review discusses existing tools for selenoprotein gene finding and other bioinformatic approaches to study the biology of selenium. Recent Advances: The availability of complete selenoproteomes allowed assessing a global distribution of the use of selenocysteine (Sec) across the tree of life, as well as studying the evolution of selenoproteins and their biosynthetic pathway. Beyond gene identification and characterization, human genetic variants in selenoprotein genes were used to examine adaptations to selenium levels in diverse human populations and to estimate selective constraints against gene loss. Critical Issues: The synthesis of selenoproteins is essential for development in mice. In humans, several mutations in selenoprotein genes have been linked to rare congenital disorders. And yet, the mechanism of Sec insertion and the regulation of selenoprotein synthesis in mammalian cells are not completely understood. Future Directions: Omics technologies offer new possibilities to study selenoproteins and mechanisms of Sec incorporation in cells, tissues, and organisms.
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Affiliation(s)
- Didac Santesmasses
- Division of Genetics, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, Massachusetts, USA
| | - Marco Mariotti
- Division of Genetics, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, Massachusetts, USA
| | - Vadim N. Gladyshev
- Division of Genetics, Department of Medicine, Harvard Medical School, Brigham and Women's Hospital, Boston, Massachusetts, USA
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8
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Schoenmakers E, Chatterjee K. Human Disorders Affecting the Selenocysteine Incorporation Pathway Cause Systemic Selenoprotein Deficiency. Antioxid Redox Signal 2020; 33:481-497. [PMID: 32295391 PMCID: PMC7409586 DOI: 10.1089/ars.2020.8097] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Significance: Generalized selenoprotein deficiency has been associated with mutations in SECISBP2, SEPSECS, and TRU-TCA1-1, 3 factors that are crucial for incorporation of the amino acid selenocysteine (Sec) into at least 25 human selenoproteins. SECISBP2 and TRU-TCA1-1 defects are characterized by a multisystem phenotype due to deficiencies of antioxidant and tissue-specific selenoproteins, together with abnormal thyroid hormone levels reflecting impaired hormone metabolism by deiodinase selenoenzymes. SEPSECS mutations are associated with a predominantly neurological phenotype with progressive cerebello-cerebral atrophy. Recent Advances: The recent identification of individuals with defects in genes encoding components of the selenocysteine insertion pathway has delineated complex and multisystem disorders, reflecting a lack of selenoproteins in specific tissues, oxidative damage due to lack of oxidoreductase-active selenoproteins and other pathways whose nature is unclear. Critical Issues: Abnormal thyroid hormone metabolism in patients can be corrected by triiodothyronine (T3) treatment. No specific therapies for other phenotypes (muscular dystrophy, male infertility, hearing loss, neurodegeneration) exist as yet, but their severity often requires supportive medical intervention. Future Directions: These disorders provide unique insights into the role of selenoproteins in humans. The long-term consequences of reduced cellular antioxidant capacity remain unknown, and future surveillance of patients may reveal time-dependent phenotypes (e.g., neoplasia, aging) or consequences of deficiency of selenoproteins whose function remains to be elucidated. The role of antioxidant therapies requires evaluation. Antioxid. Redox Signal. 33, 481-497.
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Affiliation(s)
- Erik Schoenmakers
- Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Addenbrooke's Hospital, University of Cambridge, United Kingdom
| | - Krishna Chatterjee
- Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Addenbrooke's Hospital, University of Cambridge, United Kingdom
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9
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Schomburg L. The other view: the trace element selenium as a micronutrient in thyroid disease, diabetes, and beyond. Hormones (Athens) 2020; 19:15-24. [PMID: 31823341 DOI: 10.1007/s42000-019-00150-4] [Citation(s) in RCA: 52] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2019] [Accepted: 10/21/2019] [Indexed: 02/08/2023]
Abstract
Antibiotics are provided for infections caused by bacteria, and statins help to control hypercholesterolemia. When hungry, you need to eat, and when you are deficient in a particular nutrient, the diet should be chosen wisely to provide what is missing. In the matter of providing the essential trace element selenium (Se), there are two different but partly overlapping views on its nature and requirements. Some consider it a medication that should be given to a subset of more or less well-defined (thyroid) patients only, in order to alleviate symptoms, to improve the course of the disease or even to provide a cure, alone or in an adjuvant mode. Such treatment attempts are conducted for a short time period, and potential medical benefits and side effects are evaluated thoroughly. One could also approach Se in medicine in a more holistic way and evaluate primarily the nutritional status of the patient before considering supplementation. The available evidence for positive health effects of supplemental Se can be interpreted as the consequence of correcting deficiency instead of speculating on a direct pharmaceutical action. This short review provides a novel view on Se in (thyroid) disease and beyond and offers an alternative explanation for its positive health effects, i.e., its provision of the substrate needed for allowing adequate endogenous expression of those selenoproteins that are required in certain conditions. In Se deficiency, the lack of the trace element constitutes the main limitation for the required adaptation of selenoprotein expression to counteract health risks and alleviate disease symptoms. Supplemental Se lifts this restriction and enables the full endogenous response of selenoprotein expression. However, since Se does not act as a pharmacological medication per se, it should not be viewed as a dangerous drug, and, importantly, current data show that supplemental Se does not cause diabetes.
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Affiliation(s)
- Lutz Schomburg
- Institute for Experimental Endocrinology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
- Freie Universität Berlin, Berlin, Germany.
- Humboldt-Universität zu Berlin, Berlin, Germany.
- Berlin Institute of Health, Berlin, Suedring 10, D-13353, Berlin, Germany.
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10
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Howard MT, Copeland PR. New Directions for Understanding the Codon Redefinition Required for Selenocysteine Incorporation. Biol Trace Elem Res 2019; 192:18-25. [PMID: 31342342 PMCID: PMC6801069 DOI: 10.1007/s12011-019-01827-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 07/10/2019] [Indexed: 10/26/2022]
Abstract
The fact that selenocysteine (Sec) is delivered to the elongating ribosome by a tRNA that recognizes a UGA stop codon makes it unique and a thorn in the side of what was originally thought to be a universal genetic code. The mechanism by which this redefinition occurs has been slowly coming to light over the past 30 years, but key questions remain. This review seeks to highlight the prominent mechanistic questions that will guide the direction of work in the near future. These questions arise from two major aspects of Sec incorporation: (1) novel functions for the Sec insertion sequence (SECIS) that resides in all selenoprotein mRNAs and (2) the myriad of RNA-binding proteins, both known and yet to be discovered, that act in concert to modify the translation elongation process to allow Sec incorporation.
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Affiliation(s)
- Michael T Howard
- Department of Human Genetics, University of Utah, Salt Lake City, UT, USA
| | - Paul R Copeland
- Department of Biochemistry and Molecular Biology, Rutgers Robert Wood Johnson Medical School, 675 Hoes Ln, Piscataway, NJ, 08854, USA.
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11
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Processive Recoding and Metazoan Evolution of Selenoprotein P: Up to 132 UGAs in Molluscs. J Mol Biol 2019; 431:4381-4407. [PMID: 31442478 DOI: 10.1016/j.jmb.2019.08.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 08/05/2019] [Accepted: 08/11/2019] [Indexed: 02/06/2023]
Abstract
Selenoproteins typically contain a single selenocysteine, the 21st amino acid, encoded by a context-redefined UGA. However, human selenoprotein P (SelenoP) has a redox-functioning selenocysteine in its N-terminal domain and nine selenium transporter-functioning selenocysteines in its C-terminal domain. Here we show that diverse SelenoP genes are present across metazoa with highly variable numbers of Sec-UGAs, ranging from a single UGA in certain insects, to 9 in common spider, and up to 132 in bivalve molluscs. SelenoP genes were shaped by a dynamic evolutionary process linked to selenium usage. Gene evolution featured modular expansions of an ancestral multi-Sec domain, which led to particularly Sec-rich SelenoP proteins in many aquatic organisms. We focused on molluscs, and chose Pacific oyster Magallana gigas as experimental model. We show that oyster SelenoP mRNA with 46 UGAs is translated full-length in vivo. Ribosome profiling indicates that selenocysteine specification occurs with ∼5% efficiency at UGA1 and approaches 100% efficiency at distal 3' UGAs. We report genetic elements relevant to its expression, including a leader open reading frame and an RNA structure overlapping the initiation codon that modulates ribosome progression in a selenium-dependent manner. Unlike their mammalian counterparts, the two SECIS elements in oyster SelenoP (3'UTR recoding elements) do not show functional differentiation in vitro. Oysters can increase their tissue selenium level up to 50-fold upon supplementation, which also results in extensive changes in selenoprotein expression.
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12
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Shetty SP, Sturts R, Vetick M, Copeland PR. Processive incorporation of multiple selenocysteine residues is driven by a novel feature of the selenocysteine insertion sequence. J Biol Chem 2018; 293:19377-19386. [PMID: 30323062 DOI: 10.1074/jbc.ra118.005211] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 10/05/2018] [Indexed: 11/06/2022] Open
Abstract
RNA stem loop structures have been frequently shown to regulate essential cellular processes. The selenocysteine insertion sequence (SECIS) element, found in the 3' UTRs of all selenoprotein mRNAs, is an example of such a structure, as it is required for the incorporation of the 21st amino acid, selenocysteine (Sec). Selenoprotein synthesis poses a mechanistic challenge because Sec is incorporated during translation in response to a stop codon (UGA). Although it is known that a SECIS-binding protein (SBP2) is required for Sec insertion, the mechanism of action remains elusive. Additional complexity is present in the synthesis of selenoprotein P (SELENOP), which is the only selenoprotein that contains multiple UGA codons and possesses two SECIS elements in its 3' UTR. Thus, full-length SELENOP synthesis requires processive Sec incorporation. Using zebrafish Selenop, in vitro translation assays, and 75Se labeling in HEK293 cells, we found here that processive Sec incorporation is an intrinsic property of the SECIS elements. Specifically, we identified critical features of SECIS elements that are required for processive Sec incorporation. A screen of the human SECIS elements revealed that most of these elements support processive Sec incorporation in vitro; however, we also found that the processivity of Sec incorporation into Selenop in cells is tightly regulated. We propose a model for processive Sec incorporation that involves differential recruitment of SECIS-binding proteins.
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Affiliation(s)
- Sumangala P Shetty
- From the Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, New Jersey 08854
| | - Ryan Sturts
- From the Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, New Jersey 08854
| | - Michael Vetick
- From the Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, New Jersey 08854
| | - Paul R Copeland
- From the Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, New Jersey 08854
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13
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Shetty SP, Copeland PR. The Selenium Transport Protein, Selenoprotein P, Requires Coding Sequence Determinants to Promote Efficient Selenocysteine Incorporation. J Mol Biol 2018; 430:5217-5232. [PMID: 30243837 DOI: 10.1016/j.jmb.2018.09.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Revised: 08/20/2018] [Accepted: 09/09/2018] [Indexed: 01/30/2023]
Abstract
Selenoproteins are an essential and unique group of proteins in which selenocysteine (Sec) is incorporated in response to a stop codon (UGA). Reprograming of UGA for Sec insertion in eukaryotes requires a cis-acting stem-loop structure in the 3' untranslated region of selenoprotein mRNA and several trans-acting factors. Together these factors are sufficient for Sec incorporation in vitro, but the process is highly inefficient. An additional challenge is the synthesis of selenoprotein P (SELENOP), which uniquely contains multiple UGA codons. Full-length SELENOP expression requires processive Sec incorporation, the mechanism for which is not understood. In this study, we identify core coding region sequence determinants within the SELENOP mRNA that govern SELENOP synthesis. Using 75Se labeling in cells, we determined that the N-terminal coding sequence (upstream of the second UGA) and C-terminal coding sequence context are two independent determinants for efficient synthesis of full-length SELENOP. In addition, the distance between the first UGA and the consensus signal peptide is also critical for efficiency.
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Affiliation(s)
- Sumangala P Shetty
- Department of Biochemistry and Molecular Biology, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Paul R Copeland
- Department of Biochemistry and Molecular Biology, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
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14
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Translation regulation of mammalian selenoproteins. Biochim Biophys Acta Gen Subj 2018; 1862:2480-2492. [PMID: 29751099 DOI: 10.1016/j.bbagen.2018.05.010] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Revised: 04/28/2018] [Accepted: 05/04/2018] [Indexed: 11/22/2022]
Abstract
BACKGROUND Interest in selenium research has considerably grown over the last decades owing to the association of selenium deficiencies with an increased risk of several human diseases, including cancers, cardiovascular disorders and infectious diseases. The discovery of a genetically encoded 21st amino acid, selenocysteine, is a fascinating breakthrough in molecular biology as it is the first addition to the genetic code deciphered in the 1960s. Selenocysteine is a structural and functional analog of cysteine, where selenium replaces sulfur, and its presence is critical for the catalytic activity of selenoproteins. SCOPE OF REVIEW The insertion of selenocysteine is a non-canonical translational event, based on the recoding of a UGA codon in selenoprotein mRNAs, normally used as a stop codon in other cellular mRNAs. Two RNA molecules and associated partners are crucial components of the selenocysteine insertion machinery, the Sec-tRNA[Ser]Sec devoted to UGA codon recognition and the SECIS elements located in the 3'UTR of selenoprotein mRNAs. MAJOR CONCLUSIONS The translational UGA recoding event is a limiting stage of selenoprotein expression and its efficiency is regulated by several factors. GENERAL SIGNIFICANCE The control of selenoproteome expression is crucial for redox homeostasis and antioxidant defense of mammalian organisms. In this review, we summarize current knowledge on the co-translational insertion of selenocysteine into selenoproteins, and its layers of regulation.
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15
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Shetty S, Copeland PR. Molecular mechanism of selenoprotein P synthesis. Biochim Biophys Acta Gen Subj 2018; 1862:2506-2510. [PMID: 29656121 DOI: 10.1016/j.bbagen.2018.04.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Revised: 04/06/2018] [Accepted: 04/10/2018] [Indexed: 11/26/2022]
Abstract
BACKGROUND Selenoprotein synthesis requires the reinterpretation of a UGA stop codon as one that encodes selenocysteine (Sec), a process that requires a set of dedicated translation factors. Among the mammalian selenoproteins, Selenoprotein P (SELENOP) is unique as it contains a selenocysteine-rich domain that requires multiple Sec incorporation events. SCOPE OF REVIEW In this review we elaborate on new data and current models that provide insight into how SELENOP is made. MAJOR CONCLUSIONS SELENOP synthesis requires a specific set of factors and conditions. GENERAL SIGNIFICANCE As the key protein required for proper selenium distribution, SELENOP stands out as a lynchpin selenoprotein that is essential for male fertility, proper neurologic function and selenium metabolism.
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Affiliation(s)
- Sumangala Shetty
- Department of Biochemistry and Molecular Biology, Rutgers - Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, United States
| | - Paul R Copeland
- Department of Biochemistry and Molecular Biology, Rutgers - Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, United States.
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