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Jern P, Greenwood AD. Wildlife endogenous retroviruses: colonization, consequences, and cooption. Trends Genet 2024; 40:149-159. [PMID: 37985317 DOI: 10.1016/j.tig.2023.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 10/24/2023] [Accepted: 10/31/2023] [Indexed: 11/22/2023]
Abstract
Endogenous retroviruses (ERVs) are inherited genomic remains of past germline retroviral infections. Research on human ERVs has focused on medical implications of their dysregulation on various diseases. However, recent studies incorporating wildlife are yielding remarkable perspectives on long-term retrovirus-host interactions. These initial forays into broader taxonomic analysis, including sequencing of multiple individuals per species, show the incredible plasticity and variation of ERVs within and among wildlife species. This demonstrates that stochastic processes govern much of the vertebrate genome. In this review, we elaborate on discoveries pertaining to wildlife ERV origins and evolution, genome colonization, and consequences for host biology.
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Affiliation(s)
- Patric Jern
- Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.
| | - Alex D Greenwood
- Department of Wildlife Diseases, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany; School of Veterinary Medicine, Freie Unversität Berlin, Berlin, Germany.
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2
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Azimi FC, Dean TT, Minari K, Basso LGM, Vance TDR, Serrão VHB. A Frame-by-Frame Glance at Membrane Fusion Mechanisms: From Viral Infections to Fertilization. Biomolecules 2023; 13:1130. [PMID: 37509166 PMCID: PMC10377500 DOI: 10.3390/biom13071130] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 07/09/2023] [Accepted: 07/12/2023] [Indexed: 07/30/2023] Open
Abstract
Viral entry and fertilization are distinct biological processes that share a common mechanism: membrane fusion. In viral entry, enveloped viruses attach to the host cell membrane, triggering a series of conformational changes in the viral fusion proteins. This results in the exposure of a hydrophobic fusion peptide, which inserts into the host membrane and brings the viral and host membranes into close proximity. Subsequent structural rearrangements in opposing membranes lead to their fusion. Similarly, membrane fusion occurs when gametes merge during the fertilization process, though the exact mechanism remains unclear. Structural biology has played a pivotal role in elucidating the molecular mechanisms underlying membrane fusion. High-resolution structures of the viral and fertilization fusion-related proteins have provided valuable insights into the conformational changes that occur during this process. Understanding these mechanisms at a molecular level is essential for the development of antiviral therapeutics and tools to influence fertility. In this review, we will highlight the biological importance of membrane fusion and how protein structures have helped visualize both common elements and subtle divergences in the mechanisms behind fusion; in addition, we will examine the new tools that recent advances in structural biology provide researchers interested in a frame-by-frame understanding of membrane fusion.
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Affiliation(s)
- Farshad C Azimi
- Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Trevor T Dean
- Pharmaceutical Sciences, University of Illinois Chicago, Chicago, IL 60612, USA
| | - Karine Minari
- Biomolecular Cryo-Electron Microscopy Facility, University of California-Santa Cruz, Santa Cruz, CA 95064, USA
| | - Luis G M Basso
- Laboratório de Ciências Físicas, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, Rio de Janeiro 28013-602, Brazil
| | - Tyler D R Vance
- Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Vitor Hugo B Serrão
- Biomolecular Cryo-Electron Microscopy Facility, University of California-Santa Cruz, Santa Cruz, CA 95064, USA
- Department of Chemistry and Biochemistry, University of California-Santa Cruz, Santa Cruz, CA 95064, USA
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3
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Hogan V, Johnson WE. Unique Structure and Distinctive Properties of the Ancient and Ubiquitous Gamma-Type Envelope Glycoprotein. Viruses 2023; 15:v15020274. [PMID: 36851488 PMCID: PMC9967133 DOI: 10.3390/v15020274] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 01/13/2023] [Accepted: 01/15/2023] [Indexed: 01/20/2023] Open
Abstract
After the onset of the AIDS pandemic, HIV-1 (genus Lentivirus) became the predominant model for studying retrovirus Env glycoproteins and their role in entry. However, HIV Env is an inadequate model for understanding entry of viruses in the Alpharetrovirus, Gammaretrovirus and Deltaretrovirus genera. For example, oncogenic model system viruses such as Rous sarcoma virus (RSV, Alpharetrovirus), murine leukemia virus (MLV, Gammaretrovirus) and human T-cell leukemia viruses (HTLV-I and HTLV-II, Deltaretrovirus) encode Envs that are structurally and functionally distinct from HIV Env. We refer to these as Gamma-type Envs. Gamma-type Envs are probably the most widespread retroviral Envs in nature. They are found in exogenous and endogenous retroviruses representing a broad spectrum of vertebrate hosts including amphibians, birds, reptiles, mammals and fish. In endogenous form, gamma-type Envs have been evolutionarily coopted numerous times, most notably as placental syncytins (e.g., human SYNC1 and SYNC2). Remarkably, gamma-type Envs are also found outside of the Retroviridae. Gp2 proteins of filoviruses (e.g., Ebolavirus) and snake arenaviruses in the genus Reptarenavirus are gamma-type Env homologs, products of ancient recombination events involving viruses of different Baltimore classes. Distinctive hallmarks of gamma-type Envs include a labile disulfide bond linking the surface and transmembrane subunits, a multi-stage attachment and fusion mechanism, a highly conserved (but poorly understood) "immunosuppressive domain", and activation by the viral protease during virion maturation. Here, we synthesize work from diverse retrovirus model systems to illustrate these distinctive properties and to highlight avenues for further exploration of gamma-type Env structure and function.
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Xu L, Sun S. Reconstitution of Fusion-Competent Human Placental Fusogen Syncytin-2. J Membr Biol 2022; 255:723-732. [PMID: 35596004 DOI: 10.1007/s00232-022-00242-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 05/02/2022] [Indexed: 12/24/2022]
Abstract
Mammalian placenta formation requires continuous fusion of trophoblasts. Human endogenous retrovirus-derived proteins syncytin-1 and syncytin-2 mediate cell-cell fusion of placental cytotrophoblasts to form syncytiotrophoblasts in primates, which is required for normal placenta function and fetal development. Syncytins are post-translationally cleaved by the endoprotease furin into surface (SU) and transmembrane (TM) subunits for activation. Little is currently known about the molecular mechanisms of syncytin-mediated cell-cell fusion, and their functions have not been well studied in vitro. Here, we express tagged syncytin-2 in mammalian HEK293T cells and demonstrate that the tagging greatly influences the cleavage and fusogenic activity of syncytin-2. By detecting the N-terminal tagged SU, we find that it is released into the extracellular space during the fusion process. Furthermore, when N-linked glycosylation and disulfide bond formation are blocked, the cleavage and fusogenic activity of syncytin-2 are inhibited. Finally, we were able to purify functional syncytin-2 from HEK293T cells and incorporate it into proteoliposomes. These findings lay a solid foundation for interogating the molecular mechanisms of syncytin-2-mediated cell-cell fusion in vitro.
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Affiliation(s)
- Lu Xu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071, China
| | - Sha Sun
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
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5
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Imakawa K, Kusama K, Kaneko-Ishino T, Nakagawa S, Kitao K, Miyazawa T, Ishino F. Endogenous Retroviruses and Placental Evolution, Development, and Diversity. Cells 2022; 11:cells11152458. [PMID: 35954303 PMCID: PMC9367772 DOI: 10.3390/cells11152458] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 08/01/2022] [Accepted: 08/03/2022] [Indexed: 11/16/2022] Open
Abstract
The main roles of placentas include physical protection, nutrient and oxygen import, export of gasses and fetal waste products, and endocrinological regulation. In addition to physical protection of the fetus, the placentas must provide immune protection throughout gestation. These basic functions are well-conserved; however, placentas are undoubtedly recent evolving organs with structural and cellular diversities. These differences have been explained for the last two decades through co-opting genes and gene control elements derived from transposable elements, including endogenous retroviruses (ERVs). However, the differences in placental structures have not been explained or characterized. This manuscript addresses the sorting of ERVs and their integration into the mammalian genomes and provides new ways to explain why placental structures have diverged.
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Affiliation(s)
- Kazuhiko Imakawa
- Research Institute of Agriculture, Tokai University, Kumamoto 862-8652, Japan
- Correspondence: ; Tel.: +81-96-386-2652
| | - Kazuya Kusama
- Department of Endocrine Pharmacology, Tokyo University of Pharmacy and Life Sciences, Tokyo 192-0392, Japan
| | | | - So Nakagawa
- Department of Molecular Life Science, Tokai University School of Medicine, Nakagawa 259-1193, Japan
| | - Koichi Kitao
- Laboratory of Virus-Host Coevolution, Institute for Life and Medical Sciences, Kyoto University, Kyoto 606-8507, Japan
| | - Takayuki Miyazawa
- Laboratory of Virus-Host Coevolution, Institute for Life and Medical Sciences, Kyoto University, Kyoto 606-8507, Japan
| | - Fumitoshi Ishino
- Institute of Research, Tokyo Medical and Dental University, Tokyo 113-8510, Japan
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Affiliation(s)
- Tyler D R Vance
- Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Jeffrey E Lee
- Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada.
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Štafl K, Trávníček M, Kučerová D, Pecnová Ľ, Krchlíková V, Gáliková E, Stepanets V, Hejnar J, Trejbalová K. Heterologous avian system for quantitative analysis of Syncytin-1 interaction with ASCT2 receptor. Retrovirology 2021; 18:15. [PMID: 34158079 PMCID: PMC8220723 DOI: 10.1186/s12977-021-00558-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Accepted: 06/05/2021] [Indexed: 12/29/2022] Open
Abstract
Background Human Syncytin-1 is a placentally-expressed cell surface glycoprotein of retroviral origin. After interaction with ASCT2, its cellular receptor, Syncytin-1 triggers cell–cell fusion and formation of a multinuclear syncytiotrophoblast layer of the placenta. The ASCT2 receptor is a multi-spanning membrane protein containing a protruding extracellular part called region C, which has been suggested to be a retrovirus docking site. Precise identification of the interaction site between ASCT2 and Syncytin-1 is challenging due to the complex structure of ASCT2 protein and the background of endogenous ASCT2 gene in the mammalian genome. Chicken cells lack the endogenous background and, therefore, can be used to set up a system with surrogate expression of the ASCT2 receptor. Results We have established a retroviral heterologous chicken system for rapid and reliable assessment of ectopic human ASCT2 protein expression. Our dual-fluorescence system proved successful for large-scale screening of mutant ASCT2 proteins. Using this system, we demonstrated that progressive deletion of region C substantially decreased the amount of ASCT2 protein. In addition, we implemented quantitative assays to determine the interaction of ASCT2 with Syncytin-1 at multiple levels, which included binding of the soluble form of Syncytin-1 to ASCT2 on the cell surface and a luciferase-based assay to evaluate cell–cell fusions that were triggered by Syncytin-1. Finally, we restored the envelope function of Syncytin-1 in a replication-competent retrovirus and assessed the infection of chicken cells expressing human ASCT2 by chimeric Syncytin-1-enveloped virus. The results of the quantitative assays showed that deletion of the protruding region C did not abolish the interaction of ASCT2 with Syncytin-1. Conclusions We present here a heterologous chicken system for effective assessment of the expression of transmembrane ASCT2 protein and its interaction with Syncytin-1. The system profits from the absence of endogenous ASCT2 background and implements the quantitative assays to determine the ASCT2-Syncytin-1 interaction at several levels. Using this system, we demonstrated that the protruding region C was essential for ASCT2 protein expression, but surprisingly, not for the interaction with Syncytin-1 glycoprotein. Graphical abstract ![]()
Supplementary Information The online version contains supplementary material available at 10.1186/s12977-021-00558-0.
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Affiliation(s)
- Kryštof Štafl
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic.,Faculty of Science, Charles University, Albertov 6, 12800, Prague 2, Czech Republic
| | - Martin Trávníček
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic
| | - Dana Kučerová
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic
| | - Ľubomíra Pecnová
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic
| | - Veronika Krchlíková
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic
| | - Eliška Gáliková
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic
| | - Volodymyr Stepanets
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic
| | - Jiří Hejnar
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic.
| | - Kateřina Trejbalová
- Institute of Molecular Genetics, Czech Academy of Sciences, Vídeňská 1083, 14220, Prague 4, Czech Republic.
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Conley AJ, Loux SC, Legacki EL, Stoops MA, Pukazhenthi B, Brown JL, Sattler R, French HM, Tibary A, Robeck TR. The steroid metabolome of pregnancy, insights into the maintenance of pregnancy and evolution of reproductive traits. Mol Cell Endocrinol 2021; 528:111241. [PMID: 33711335 DOI: 10.1016/j.mce.2021.111241] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 03/01/2021] [Accepted: 03/03/2021] [Indexed: 11/28/2022]
Abstract
Modes of mammalian reproduction are diverse and not always conserved among related species. Progesterone is universally required to supports pregnancy but sites of synthesis and metabolic pathways vary widely. The steroid metabolome of mid-to late gestation was characterized, focusing on 5α-reduced pregnanes in species representing the Perissodactyla, Cetartiodactyla and Carnivora using mass spectrometry. Metabolomes and steroidogenic enzyme ortholog sequences were used in heirarchial analyses. Steroid metabolite profiles were similar within orders, whales within cetartiodactyls for instance, but with notable exceptions such as rhinoceros clustering with goats, and tapirs with pigs. Steroidogenic enzyme sequence clustering reflected expected evolutionary relationships but once again with exceptions. Human sequences (expected outgroups) clustered with perissodactyl CYP11A1, CYP17A1 and SRD5A1 gene orthologues, forming outgroups only for HSD17B1 and SRD5A2. Spotted hyena CYP19A1 clustered within the Perissodactyla, between rhinoceros and equid orthologues, whereas CYP17A1 clustered within the Carnivora. This variability highlights the random adoption of divergent physiological strategies as pregnancy evolved among genetically similar species.
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Affiliation(s)
- A J Conley
- Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, CA, USA.
| | - S C Loux
- Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, USA
| | - E L Legacki
- Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, CA, USA; Hollings Marine Laboratory, National Institute of Standards & Technology, Charleston, SC, USA
| | - M A Stoops
- Omaha's Henry Doorly Zoo and Aquarium, Omaha, NE, USA
| | - B Pukazhenthi
- Center for Species Survival, Smithsonian Conservation Biology Institute, Front Royal, VA, USA
| | - J L Brown
- Center for Species Survival, Smithsonian Conservation Biology Institute, Front Royal, VA, USA
| | - R Sattler
- Alaska Department of Fish and Game, Palmer, AK, USA
| | - H M French
- Department of Clinical Sciences, Ross University School of Veterinary Medicine, St. Kitts, West Indies
| | - A Tibary
- Comparative Theriogenology, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA, USA
| | - T R Robeck
- Zoological Operations, SeaWorld Parks and Entertainment, Orlando, FL, USA
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Exaptation of Retroviral Syncytin for Development of Syncytialized Placenta, Its Limited Homology to the SARS-CoV-2 Spike Protein and Arguments against Disturbing Narrative in the Context of COVID-19 Vaccination. BIOLOGY 2021; 10:biology10030238. [PMID: 33808658 PMCID: PMC8003504 DOI: 10.3390/biology10030238] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 03/15/2021] [Accepted: 03/17/2021] [Indexed: 12/21/2022]
Abstract
Simple Summary The anti-vaccination movement claims an alleged danger of the COVID-19 vaccine based on the presupposed similarity between syncytin, which plays a role in human placentation and the SARS-CoV-2 spike protein. We argue that because of very low sequence similarity between human syncytin-1 and the SARS-CoV-2 S protein, it is unlikely that any S protein-specific SARS-CoV-2 vaccine would generate an immune response which would affect fertility and pregnancy. However, further evaluation of potential impacts of COVID-19 vaccines on fertility, placentation, pregnancy and general health of mother and newborn is required. Abstract Human placenta formation relies on the interaction between fused trophoblast cells of the embryo with uterine endometrium. The fusion between trophoblast cells, first into cytotrophoblast and then into syncytiotrophoblast, is facilitated by the fusogenic protein syncytin. Syncytin derives from an envelope glycoprotein (ENV) of retroviral origin. In exogenous retroviruses, the envelope glycoproteins coded by env genes allow fusion of the viral envelope with the host cell membrane and entry of the virus into a host cell. During mammalian evolution, the env genes have been repeatedly, and independently, captured by various mammalian species to facilitate the formation of the placenta. Such a shift in the function of a gene, or a trait, for a different purpose during evolution is called an exaptation (co-option). We discuss the structure and origin of the placenta, the fusogenic and non-fusogenic functions of syncytin, and the mechanism of cell fusion. We also comment on an alleged danger of the COVID-19 vaccine based on the presupposed similarity between syncytin and the SARS-CoV-2 spike protein.
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10
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Zhang X, Muglia LJ. Baby's best Foe-riend: Endogenous retroviruses and the evolution of eutherian reproduction. Placenta 2021; 113:1-7. [PMID: 33685754 DOI: 10.1016/j.placenta.2021.02.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 02/07/2021] [Accepted: 02/18/2021] [Indexed: 11/18/2022]
Abstract
High maternal investment in pregnancy and the perinatal period are prominent features of eutherian reproduction. Viviparity increases offspring survival, favoring high maternal prenatal investment. Matrotrophy through the placenta reduces maternal investment at early pregnancy, allowing the mother to abort embryos of subpar quality, therefore reducing resources wastage. On the other hand, intimate maternal-fetal interplay enables the fetus to manipulate maternal physiology to acquire more resources. This parent-offspring conflict likely drives the evolution of eutherian placentation, which is facilitated by the endogenous retroviruses (ERVs), ancient retroviruses that invaded host genome millions of years ago. ERVs bring new genes and novel regulatory elements into host genome, contribute to maternal-fetal tolerance, placenta-specific cell type formation, trophoblast gene expression network rewiring, and the establishment of imprinting. However, retroviruses/ERVs can function as infectious pathogens that interfere with host immune and inflammation pathways and cause genomic instability. In addition, ERVs coopted for host function may contribute to pathogenesis during infections due to their susceptibility to mechanisms activated by the invading pathogens. ERVs have been implicated in multiple perinatal adverse outcomes, therefore, eutherians must have evolved control mechanisms to regulate their function. Here we propose the TRIM family as an important participant of host antiviral defense and a likely candidate that mediates the coevolution of ERVs and their eutherian host. TRIMs have been shown to interact with retroviruses during each step of the infectious cycle. Understanding TRIMs' role in ERV regulation in the placenta may provide insight to both the physiology and pathology of eutherian reproduction.
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Affiliation(s)
- Xuzhe Zhang
- March of Dimes Prematurity Research Center Ohio Collaborative, Cincinnati, OH, USA; Division of Human Genetics, Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.
| | - Louis J Muglia
- March of Dimes Prematurity Research Center Ohio Collaborative, Cincinnati, OH, USA; Division of Human Genetics, Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA; Burroughs Wellcome Fund, Research Triangle Park, NC, USA.
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Cottee MA, Letham SC, Young GR, Stoye JP, Taylor IA. Structure of Drosophila melanogaster ARC1 reveals a repurposed molecule with characteristics of retroviral Gag. SCIENCE ADVANCES 2020; 6:eaay6354. [PMID: 31911950 PMCID: PMC6938703 DOI: 10.1126/sciadv.aay6354] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 11/06/2019] [Indexed: 06/10/2023]
Abstract
The tetrapod neuronal protein ARC and its Drosophila melanogaster homolog, dARC1, have important but differing roles in neuronal development. Both are thought to originate through exaptation of ancient Ty3/Gypsy retrotransposon Gag, with their novel function relying on an original capacity for self-assembly and encapsidation of nucleic acids. Here, we present the crystal structure of dARC1 CA and examine the relationship between dARC1, mammalian ARC, and the CA protein of circulating retroviruses. We show that while the overall architecture is highly related to that of orthoretroviral and spumaretroviral CA, there are substantial deviations in both amino- and carboxyl-terminal domains, potentially affecting recruitment of partner proteins and particle assembly. The degree of sequence and structural divergence suggests that Ty3/Gypsy Gag has been exapted on two separate occasions and that, although mammalian ARC and dARC1 share functional similarity, the structures have undergone different adaptations after appropriation into the tetrapod and insect genomes.
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Affiliation(s)
- Matthew A. Cottee
- Macromolecular Structure Laboratory, The Francis Crick Institute, Midland Road, London NW1 1AT, UK
| | - Suzanne C. Letham
- Macromolecular Structure Laboratory, The Francis Crick Institute, Midland Road, London NW1 1AT, UK
| | - George R. Young
- Retrovirus-Host Interactions Laboratory, The Francis Crick Institute, Midland Road, London NW1 1AT, UK
| | - Jonathan P. Stoye
- Retrovirus-Host Interactions Laboratory, The Francis Crick Institute, Midland Road, London NW1 1AT, UK
- Department of Medicine, Imperial College London, London SW7 2AZ, UK
| | - Ian A. Taylor
- Macromolecular Structure Laboratory, The Francis Crick Institute, Midland Road, London NW1 1AT, UK
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