1
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Simpson J, Kozak CA, Boso G. Evolutionary conservation of an ancient retroviral gagpol gene in Artiodactyla. J Virol 2023; 97:e0053523. [PMID: 37668369 PMCID: PMC10537755 DOI: 10.1128/jvi.00535-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Accepted: 06/28/2023] [Indexed: 09/06/2023] Open
Abstract
The genomes of mammals contain fingerprints of past infections by ancient retroviruses that invaded the germline of their ancestors. Most of these endogenous retroviruses (ERVs) contain only remnants of the original retrovirus; however, on rare occasions, ERV genes can be co-opted for a beneficial host function. While most studies of co-opted ERVs have focused on envelope genes, including the syncytins that function in placentation, there are examples of co-opted gag genes including one we recently discovered in simian primates. Here, we searched for other intact gag genes in non-primate mammalian lineages. We began by examining the genomes of extant camel species, which represent a basal lineage in the order Artiodactyla. This identified a gagpol gene with a large open reading frame (ORF) (>3,500 bp) in the same orthologous location in Artiodactyla species but that is absent in other mammals. Thus, this ERV was fixed in the common ancestor of all Artiodactyla at least 64 million years ago. The amino acid sequence of this gene, termed ARTgagpol, contains recognizable matrix, capsid, nucleocapsid, and reverse transcriptase domains in ruminants, with an RNase H domain in camels and pigs. Phylogenetic analysis and structural prediction of its reverse transcriptase and RNase H domains groups ARTgagpol with gammaretroviruses. Transcriptomic analysis shows ARTgagpol expression in multiple tissues suggestive of a co-opted host function. These findings identify the oldest and largest ERV-derived gagpol gene with an intact ORF in mammals, an intriguing milestone in the co-evolution of mammals and retroviruses. IMPORTANCE Retroviruses are unique among viruses that infect animals as they integrate their reverse-transcribed double-stranded DNA into host chromosomes. When this happens in a germline cell, such as sperm, egg, or their precursors, the integrated retroviral copies can be passed on to the next generation as endogenous retroviruses (ERVs). On rare occasions, the genes of these ERVs can be domesticated by the host. In this study we used computational similarity searches to identify an ancient ERV with an intact viral gagpol gene in the genomes of camels that is also found in the same genomic location in other even-toed ungulates suggesting that it is at least 64 million years old. Broad tissue expression and predicted preservation of the reverse transcriptase fold of this protein suggest that it may be domesticated for a host function. This is the oldest known intact gagpol gene of an ancient retrovirus in mammals.
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Affiliation(s)
- J'Zaria Simpson
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA
| | - Christine A. Kozak
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA
| | - Guney Boso
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, USA
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2
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Chabukswar S, Grandi N, Lin LT, Tramontano E. Envelope Recombination: A Major Driver in Shaping Retroviral Diversification and Evolution within the Host Genome. Viruses 2023; 15:1856. [PMID: 37766262 PMCID: PMC10536682 DOI: 10.3390/v15091856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 08/21/2023] [Accepted: 08/29/2023] [Indexed: 09/29/2023] Open
Abstract
Endogenous retroviruses (ERVs) are integrated into host DNA as the result of ancient germ line infections, primarily by extinct exogenous retroviruses. Thus, vertebrates' genomes contain thousands of ERV copies, providing a "fossil" record for ancestral retroviral diversity and its evolution within the host genome. Like other retroviruses, the ERV proviral sequence consists of gag, pro, pol, and env genes flanked by long terminal repeats (LTRs). Particularly, the env gene encodes for the envelope proteins that initiate the infection process by binding to the host cellular receptor(s), causing membrane fusion. For this reason, a major element in understanding ERVs' evolutionary trajectory is the characterization of env changes over time. Most of the studies dedicated to ERVs' env have been aimed at finding an "actual" physiological or pathological function, while few of them have focused on how these genes were once acquired and modified within the host. Once acquired into the organism, genome ERVs undergo common cellular events, including recombination. Indeed, genome recombination plays a role in ERV evolutionary dynamics. Retroviral recombination events that might have been involved in env divergence include the acquisition of env genes from distantly related retroviruses, env swapping facilitating multiple cross-species transmission over millions of years, ectopic recombination between the homologous sequences present in different positions in the chromosomes, and template switching during transcriptional events. The occurrence of these recombinational events might have aided in shaping retroviral diversification and evolution until the present day. Hence, this review describes and discusses in detail the reported recombination events involving ERV env to provide the basis for further studies in the field.
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Affiliation(s)
- Saili Chabukswar
- Laboratory of Molecular Virology, Department of Life and Environmental Sciences, University of Cagliari, 09042 Cagliari, Italy; (S.C.); (N.G.)
- International Ph.D. Program in Medicine, College of Medicine, Taipei Medical University, Taipei 110, Taiwan
| | - Nicole Grandi
- Laboratory of Molecular Virology, Department of Life and Environmental Sciences, University of Cagliari, 09042 Cagliari, Italy; (S.C.); (N.G.)
| | - Liang-Tzung Lin
- Department of Microbiology and Immunology, School of Medicine, College of Medicine, Taipei Medical University, Taipei 110, Taiwan;
- Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei 110, Taiwan
| | - Enzo Tramontano
- Laboratory of Molecular Virology, Department of Life and Environmental Sciences, University of Cagliari, 09042 Cagliari, Italy; (S.C.); (N.G.)
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3
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Wang Q, Shi Y, Bian Q, Zhang N, Wang M, Wang J, Li X, Lai L, Zhao Z, Yu H. Molecular mechanisms of syncytin-1 in tumors and placental development related diseases. Discov Oncol 2023; 14:104. [PMID: 37326913 DOI: 10.1007/s12672-023-00702-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2023] [Accepted: 05/25/2023] [Indexed: 06/17/2023] Open
Abstract
Human endogenous retroviruses (HERVs) have evolved from exogenous retroviruses and account for approximately 8% of the human genome. A growing number of findings suggest that the abnormal expression of HERV genes is associated with schizophrenia, multiple sclerosis, endometriosis, breast cancer, bladder cancer and other diseases. HERV-W env (syncytin-1) is a membrane glycoprotein which plays an important role in placental development. It includes embryo implantation, fusion of syncytiotrophoblasts and of fertilized eggs, and immune response. The abnormal expression of syncytin-1 is related to placental development-related diseases such as preeclampsia, infertility, and intrauterine growth restriction, as well as tumors such as neuroblastoma, endometrial cancer, and endometriosis. This review mainly focused on the molecular interactions of syncytin-1 in placental development-related diseases and tumors, to explore whether syncytin-1 can be an emerging biological marker and potential therapeutic target.
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Affiliation(s)
- Qianqian Wang
- Department of Biochemistry, Jining Medical University, 133 Hehua Road, Jining, 272067, Shandong, People's Republic of China
| | - Ying Shi
- Department of Biochemistry, Jining Medical University, 133 Hehua Road, Jining, 272067, Shandong, People's Republic of China
| | - Qiang Bian
- Collaborative Innovation Center, Jining Medical University, Jining, 272067, Shandong, People's Republic of China
- Department of Pathophysiology, Weifang Medical University, Weifang, 261053, Shandong, People's Republic of China
| | - Naibin Zhang
- Department of Biochemistry, Jining Medical University, 133 Hehua Road, Jining, 272067, Shandong, People's Republic of China
| | - Meng Wang
- Department of Biochemistry, Jining Medical University, 133 Hehua Road, Jining, 272067, Shandong, People's Republic of China
| | - Jianing Wang
- Department of Biochemistry, Jining Medical University, 133 Hehua Road, Jining, 272067, Shandong, People's Republic of China
| | - Xuan Li
- Department of Biochemistry, Jining Medical University, 133 Hehua Road, Jining, 272067, Shandong, People's Republic of China
| | - Luhao Lai
- Collaborative Innovation Center, Jining Medical University, Jining, 272067, Shandong, People's Republic of China
| | - Zhankui Zhao
- The Affiliated Hospital of Jining Medical University, Jining Medical University, 89 Guhuai Road, Jining, 272029, Shandong, People's Republic of China.
| | - Honglian Yu
- Department of Biochemistry, Jining Medical University, 133 Hehua Road, Jining, 272067, Shandong, People's Republic of China.
- Collaborative Innovation Center, Jining Medical University, Jining, 272067, Shandong, People's Republic of China.
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4
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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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Structural insights into the lysophospholipid brain uptake mechanism and its inhibition by syncytin-2. Nat Struct Mol Biol 2022; 29:604-612. [PMID: 35710838 DOI: 10.1038/s41594-022-00786-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 05/01/2022] [Indexed: 12/29/2022]
Abstract
Brain development and function require uptake of essential omega-3 fatty acids in the form of lysophosphatidylcholine via major-facilitator superfamily transporter MFSD2A, a potential pharmaceutical target to modulate blood-brain barrier (BBB) permeability. MFSD2A is also the receptor of endogenous retroviral envelope syncytin-2 (SYNC2) in human placenta, where it mediates cell-cell fusion and formation of the maternal-fetal interface. Here, we report a cryo-electron microscopy structure of the human MFSD2A-SYNC2 complex that reveals a large hydrophobic cavity in the transporter C-terminal domain to occlude long aliphatic chains. The transporter architecture suggests an alternating-access transport mechanism for lipid substrates in mammalian MFS transporters. SYNC2 establishes an extensive binding interface with MFSD2A, and a SYNC2-soluble fragment acts as a long-sought-after inhibitor of MFSD2A transport. Our work uncovers molecular mechanisms important to brain and placenta development and function, and SYNC2-mediated inhibition of MFSD2A transport suggests strategies to aid delivery of therapeutic macromolecules across the BBB.
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6
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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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7
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Lokossou AG, Toudic C, Nguyen PT, Elisseeff X, Vargas A, Rassart É, Lafond J, Leduc L, Bourgault S, Gilbert C, Scorza T, Tolosa J, Barbeau B. Endogenous retrovirus-encoded Syncytin-2 contributes to exosome-mediated immunosuppression of T cells†. Biol Reprod 2021; 102:185-198. [PMID: 31318021 DOI: 10.1093/biolre/ioz124] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 12/21/2018] [Accepted: 07/11/2019] [Indexed: 12/24/2022] Open
Abstract
Modulation of the activation status of immune cell populations during pregnancy depends on placental villous cytotrophoblast (VCT) cells and the syncytiotrophoblast (STB). Failure in the establishment of this immunoregulatory function leads to pregnancy complications. Our laboratory has been studying Syncytin-2 (Syn-2), an endogenous retroviral protein expressed in placenta and on the surface of placental exosomes. This protein plays an important role not only in STB formation through its fusogenic properties, but also through its immunosuppressive domain (ISD). Considering that Syn-2 expression is importantly reduced in preeclamptic placentas, we were interested in addressing its possible immunoregulatory effects on T cells. Activated Jurkat T cells and peripheral blood mononuclear cells (PBMCs) were treated with monomeric or dimerized version of a control or a Syn-2 ISD peptide. Change in phosphorylation levels of ERK1/2 MAP kinases was selectively noted in Jurkat cells treated with the dimerized ISD peptide. Upon incubation with the dimerized Syn-2 ISD peptide, significant reduction in Th1 cytokine production was further demonstrated by ELISA and Human Th1/Th2 Panel Multi-Analyte Flow Assay. To determine if exosome-associated Syn-2 could also be immunosuppressive placental exosomes were incubated with activated Jurkat and PBMCs. Quantification of Th1 cytokines in the supernatants revealed severe reduction in T cell activation. Interestingly, exosomes from Syn-2-silenced VCT incubated with PBMCs were less suppressive when compared with exosome derived from VCT transfected with control small interfering RNA (siRNA). Our results suggest that Syn-2 is an important immune regulator both locally and systemically, via its association with placental exosomes.
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Affiliation(s)
- Adjimon G Lokossou
- Université du Québec à Montréal, Department of Biological Sciences, Montreal, Quebec, Canada.,Centre de recherche BioMed, Montreal, Quebec, Canada
| | - Caroline Toudic
- Université du Québec à Montréal, Department of Biological Sciences, Montreal, Quebec, Canada.,Centre de recherche BioMed, Montreal, Quebec, Canada
| | - Phuong Trang Nguyen
- Centre de recherche BioMed, Montreal, Quebec, Canada.,Université du Québec à Montréal, Department of Chemistry, Montreal, Quebec, Canada
| | - Xavier Elisseeff
- Université du Québec à Montréal, Department of Biological Sciences, Montreal, Quebec, Canada.,Centre de recherche BioMed, Montreal, Quebec, Canada
| | - Amandine Vargas
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Université de Montréal, Saint-Hyacinthe, Quebec, Canada
| | - Éric Rassart
- Université du Québec à Montréal, Department of Biological Sciences, Montreal, Quebec, Canada.,Centre de recherche BioMed, Montreal, Quebec, Canada
| | - Julie Lafond
- Université du Québec à Montréal, Department of Biological Sciences, Montreal, Quebec, Canada.,Centre de recherche BioMed, Montreal, Quebec, Canada
| | - Line Leduc
- CHU Ste-Justine, Montreal, Quebec, Canada
| | - Steve Bourgault
- Centre de recherche BioMed, Montreal, Quebec, Canada.,Université du Québec à Montréal, Department of Chemistry, Montreal, Quebec, Canada.,Centre d'Excellence en Recherche sur les Maladies Orphelines-Fondation Courtois, Montreal, Quebec, Canada
| | | | - Tatiana Scorza
- Université du Québec à Montréal, Department of Biological Sciences, Montreal, Quebec, Canada.,Centre de recherche BioMed, Montreal, Quebec, Canada.,Centre d'Excellence en Recherche sur les Maladies Orphelines-Fondation Courtois, Montreal, Quebec, Canada
| | - Jorge Tolosa
- Mothers and Babies Research Centre and Hunter Medical Research Institute, The University of Newcastle, Newcastle, Australia
| | - Benoit Barbeau
- Université du Québec à Montréal, Department of Biological Sciences, Montreal, Quebec, Canada.,Centre de recherche BioMed, Montreal, Quebec, Canada.,Centre d'Excellence en Recherche sur les Maladies Orphelines-Fondation Courtois, Montreal, Quebec, Canada
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8
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Chan KMC, Son S, Schmid EM, Fletcher DA. A viral fusogen hijacks the actin cytoskeleton to drive cell-cell fusion. eLife 2020; 9:51358. [PMID: 32441254 PMCID: PMC7244324 DOI: 10.7554/elife.51358] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 05/08/2020] [Indexed: 01/01/2023] Open
Abstract
Cell-cell fusion, which is essential for tissue development and used by some viruses to form pathological syncytia, is typically driven by fusogenic membrane proteins with tall (>10 nm) ectodomains that undergo conformational changes to bring apposing membranes in close contact prior to fusion. Here we report that a viral fusogen with a short (<2 nm) ectodomain, the reptilian orthoreovirus p14, accomplishes the same task by hijacking the actin cytoskeleton. We show that phosphorylation of the cytoplasmic domain of p14 triggers N-WASP-mediated assembly of a branched actin network. Using p14 mutants, we demonstrate that fusion is abrogated when binding of an adaptor protein is prevented and that direct coupling of the fusogenic ectodomain to branched actin assembly is sufficient to drive cell-cell fusion. This work reveals how the actin cytoskeleton can be harnessed to overcome energetic barriers to cell-cell fusion.
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Affiliation(s)
- Ka Man Carmen Chan
- UC Berkeley-UC San Francisco Graduate Group in Bioengineering, Berkeley, United States.,Department of Bioengineering & Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
| | - Sungmin Son
- Department of Bioengineering & Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
| | - Eva M Schmid
- Department of Bioengineering & Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
| | - Daniel A Fletcher
- UC Berkeley-UC San Francisco Graduate Group in Bioengineering, Berkeley, United States.,Department of Bioengineering & Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States.,Division of Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, United States.,Chan Zuckerberg Biohub, San Francisco, United States
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9
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X-ray Structures of the Post-fusion 6-Helix Bundle of the Human Syncytins and their Functional Implications. J Mol Biol 2019; 431:4922-4940. [PMID: 31711961 PMCID: PMC7094397 DOI: 10.1016/j.jmb.2019.10.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 10/22/2019] [Accepted: 10/23/2019] [Indexed: 12/27/2022]
Abstract
The retroviral envelope-derived proteins syncytin-1 and syncytin-2 (syn1 and syn2) drive placentation in humans by forming a syncytiotophoblast, a structure allowing for an exchange interface between maternal and fetal blood during pregnancy. Despite their essential role, little is known about the molecular mechanism underlying the syncytins' function. We report here the X-ray structures of the syn1 and syn2 transmembrane subunit ectodomains, featuring a 6-helix bundle (6HB) typical of the post-fusion state of gamma-retrovirus and filovirus fusion proteins. Contrary to the filoviruses, for which the fusion glycoprotein was crystallized both in the post-fusion and in the spring-loaded pre-fusion form, the highly unstable nature of the syncytins' prefusion form has precluded structural studies. We undertook a proline-scanning approach searching for regions in the syn1 6HB central helix that tolerate the introduction of helix-breaker residues and still fold correctly in the pre-fusion form. We found that there is indeed such a region, located two α-helical turns downstream a stutter in the central coiled-coil helix - precisely where the breaks of the spring-loaded helix of the filoviruses map. These mutants were fusion-inactive as they cannot form the 6HB, similar to the “SOSIP” mutant of HIV Env that allowed the high-resolution structural characterization of its labile pre-fusion form. These results now open a new window of opportunity to engineer more stable variants of the elusive pre-fusion trimer of the syncytins and other gamma-retroviruses envelope proteins for structural characterization. A typical retroviral γ-type Env protein 6-helix bundle in post-fusion syncytins. An extensive ionic interactions network correlates with higher stability of syn1. Spring-loaded pre-fusion form hinted by structural homology with filoviruses. Helix-breaking residues in the central coiled-coil allow folding in pre-fusion form.
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10
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Edwardson TGW, Hilvert D. Virus-Inspired Function in Engineered Protein Cages. J Am Chem Soc 2019; 141:9432-9443. [PMID: 31117660 DOI: 10.1021/jacs.9b03705] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The structural and functional diversity of proteins combined with their genetic programmability has made them indispensable modern materials. Well-defined, hollow protein capsules have proven to be particularly useful due to their ability to compartmentalize macromolecules and chemical processes. To this end, viral capsids are common scaffolds and have been successfully repurposed to produce a suite of practical protein-based nanotechnologies. Recently, the recapitulation of viromimetic function in protein cages of nonviral origin has emerged as a strategy to both complement physical studies of natural viruses and produce useful scaffolds for diverse applications. In this perspective, we review recent progress toward generation of virus-like behavior in nonviral protein cages through rational engineering and directed evolution. These artificial systems can aid our understanding of the emergence of viruses from existing cellular components, as well as provide alternative approaches to tackle current problems, and open up new opportunities, in medicine and biotechnology.
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Affiliation(s)
| | - Donald Hilvert
- Laboratory of Organic Chemistry , ETH Zurich , 8093 Zurich , Switzerland
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11
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Grandi N, Tramontano E. HERV Envelope Proteins: Physiological Role and Pathogenic Potential in Cancer and Autoimmunity. Front Microbiol 2018; 9:462. [PMID: 29593697 PMCID: PMC5861771 DOI: 10.3389/fmicb.2018.00462] [Citation(s) in RCA: 135] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 02/27/2018] [Indexed: 12/29/2022] Open
Abstract
Human endogenous retroviruses (HERVs) are relics of ancient infections accounting for about the 8% of our genome. Despite their persistence in human DNA led to the accumulation of mutations, HERVs are still contributing to the human transcriptome, and a growing number of findings suggests that their expression products may have a role in various diseases. Among HERV products, the envelope proteins (Env) are currently highly investigated for their pathogenic properties, which could likely be participating to several disorders with complex etiology, particularly in the contexts of autoimmunity and cancer. In fact, HERV Env proteins have been shown, on the one side, to trigger both innate and adaptive immunity, prompting inflammatory, cytotoxic and apoptotic reactions; and, on the other side, to prevent the immune response activation, presenting immunosuppressive properties and acting as immune downregulators. In addition, HERV Env proteins have been shown to induce abnormal cell-cell fusion, possibly contributing to tumor development and metastasizing processes. Remarkably, even highly defective HERV env genes and alternative env splicing variants can provide further mechanisms of pathogenesis. A well-known example is the HERV-K(HML2) env gene that, depending on the presence or the absence of a 292-bp deletion, can originate two proteins of different length (Np9 and Rec) proposed to have oncogenic properties. The understanding of their involvement in complex pathological disorders made HERV Env proteins potential targets for therapeutic interventions. Of note, a monoclonal antibody directed against a HERV-W Env is currently under clinical trial as therapeutic approach for multiple sclerosis, representing the first HERV-based treatment. The present review will focus on the current knowledge of the HERV Env expression, summarizing its role in human physiology and its possible pathogenic effects in various cancer and autoimmune disorders. It moreover analyzes HERV Env possible exploitation for the development of innovative therapeutic strategies.
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Affiliation(s)
- Nicole Grandi
- Laboratory of Molecular Virology, Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy
| | - Enzo Tramontano
- Laboratory of Molecular Virology, Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy
- Istituto di Ricerca Genetica e Biomedica, Consiglio Nazionale delle Ricerche, Cagliari, Italy
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12
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Brütting C, Narasimhan H, Hoffmann F, Kornhuber ME, Staege MS, Emmer A. Investigation of Endogenous Retrovirus Sequences in the Neighborhood of Genes Up-regulated in a Neuroblastoma Model after Treatment with Hypoxia-Mimetic Cobalt Chloride. Front Microbiol 2018. [PMID: 29515560 PMCID: PMC5826361 DOI: 10.3389/fmicb.2018.00287] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human endogenous retroviruses (ERVs) have been found to be associated with different diseases, e.g., multiple sclerosis (MS). Most human ERVs integrated in our genome are not competent to replicate and these sequences are presumably silent. However, transcription of human ERVs can be reactivated, e.g., by hypoxia. Interestingly, MS has been linked to hypoxia since decades. As some patterns of demyelination are similar to white matter ischemia, hypoxic damage is discussed. Therefore, we are interested in the association between hypoxia and ERVs. As a model, we used human SH-SY5Y neuroblastoma cells after treatment with the hypoxia-mimetic cobalt chloride and analyzed differences in the gene expression profiles in comparison to untreated cells. The vicinity of up-regulated genes was scanned for endogenous retrovirus-derived sequences. Five genes were found to be strongly up-regulated in SH-SY5Y cells after treatment with cobalt chloride: clusterin, glutathione peroxidase 3, insulin-like growth factor 2, solute carrier family 7 member 11, and neural precursor cell expressed developmentally down-regulated protein 9. In the vicinity of these genes we identified large (>1,000 bp) open reading frames (ORFs). Most of these ORFs showed only low similarities to proteins from retro-transcribing viruses. However, we found very high similarity between retrovirus envelope sequences and a sequence in the vicinity of neural precursor cell expressed developmentally down-regulated protein 9. This sequence encodes the human endogenous retrovirus group FRD member 1, the encoded protein product is called syncytin 2. Transfection of syncytin 2 into the well-characterized Ewing sarcoma cell line A673 was not able to modulate the low immunostimulatory activity of this cell line. Future research is needed to determine whether the identified genes and the human endogenous retrovirus group FRD member 1 might play a role in the etiology of MS.
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Affiliation(s)
- Christine Brütting
- Department of Surgical and Conservative Paediatrics and Adolescent Medicine, Martin Luther University of Halle-Wittenberg, Halle, Germany.,Department of Neurology, Martin Luther University of Halle-Wittenberg, Halle, Germany
| | - Harini Narasimhan
- Department of Surgical and Conservative Paediatrics and Adolescent Medicine, Martin Luther University of Halle-Wittenberg, Halle, Germany
| | - Frank Hoffmann
- Department of Neurology, Hospital "Martha-Maria" Halle-Dölau, Halle, Germany
| | - Malte E Kornhuber
- Department of Neurology, Martin Luther University of Halle-Wittenberg, Halle, Germany
| | - Martin S Staege
- Department of Surgical and Conservative Paediatrics and Adolescent Medicine, Martin Luther University of Halle-Wittenberg, Halle, Germany
| | - Alexander Emmer
- Department of Neurology, Martin Luther University of Halle-Wittenberg, Halle, Germany
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13
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Abstract
Cell-cell fusion is essential for fertilization and organ development. Dedicated proteins known as fusogens are responsible for mediating membrane fusion. However, until recently, these proteins either remained unidentified or were poorly understood at the mechanistic level. Here, we review how fusogens surmount multiple energy barriers to mediate cell-cell fusion. We describe how early preparatory steps bring membranes to a distance of ∼10 nm, while fusogens act in the final approach between membranes. The mechanical force exerted by cell fusogens and the accompanying lipidic rearrangements constitute the hallmarks of cell-cell fusion. Finally, we discuss the relationship between viral and eukaryotic fusogens, highlight a classification scheme regrouping a superfamily of fusogens called Fusexins, and propose new questions and avenues of enquiry.
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Affiliation(s)
- Javier M Hernández
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, D-44227 Dortmund, Germany
| | - Benjamin Podbilewicz
- Department of Biology, Technion - Israel Institute of Technology, Haifa 32000, Israel
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14
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Malhotra SS, Banerjee P, Gupta SK. Regulation of trophoblast differentiation during embryo implantation and placentation: Implications in pregnancy complications. ACTA ACUST UNITED AC 2016. [DOI: 10.1016/j.jrhm.2016.10.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Soulavie F, Sundaram MV. Auto-fusion and the shaping of neurons and tubes. Semin Cell Dev Biol 2016; 60:136-145. [PMID: 27436685 DOI: 10.1016/j.semcdb.2016.07.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Revised: 07/15/2016] [Accepted: 07/15/2016] [Indexed: 12/14/2022]
Abstract
Cells adopt specific shapes that are necessary for specific functions. For example, some neurons extend elaborate arborized dendrites that can contact multiple targets. Epithelial and endothelial cells can form tiny seamless unicellular tubes with an intracellular lumen. Recent advances showed that cells can auto-fuse to acquire those specific shapes. During auto-fusion, a cell merges two parts of its own plasma membrane. In contrast to cell-cell fusion or macropinocytic fission, which result in the merging or formation of two separate membrane bound compartments, auto-fusion preserves one compartment, but changes its shape. The discovery of auto-fusion in C. elegans was enabled by identification of specific protein fusogens, EFF-1 and AFF-1, that mediate cell-cell fusion. Phenotypic characterization of eff-1 and aff-1 mutants revealed that fusogen-mediated fusion of two parts of the same cell can be used to sculpt dendritic arbors, reconnect two parts of an axon after injury, or form a hollow unicellular tube. Similar auto-fusion events recently were detected in vertebrate cells, suggesting that auto-fusion could be a widely used mechanism for shaping neurons and tubes.
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Affiliation(s)
- Fabien Soulavie
- Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA 19104,United States
| | - Meera V Sundaram
- Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA 19104,United States.
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16
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Cui L, Wang H, Lu X, Wang R, Zheng R, Li Y, Yang X, Jia WT, Zhao Y, Wang Y, Wang H, Wang YL, Zhu C, Lin HY, Wang H. Effects of individually silenced N-glycosylation sites and non-synonymous single-nucleotide polymorphisms on the fusogenic function of human syncytin-2. Cell Adh Migr 2016; 10:39-55. [PMID: 26853155 PMCID: PMC4853038 DOI: 10.1080/19336918.2015.1093720] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The placental syncytiotrophoblast, which is formed by the fusion of cytotrophoblast cells, is indispensable for the establishment and maintenance of normal pregnancy. The human endogenous retrovirus envelope glycoprotein syncytin-2 is the most important player in mediating trophoblast cell-cell fusion as a fusogen. We constructed expression plasmids of wild-type and 21 single-amino-acid substitution mutants of syncytin-2, including 10 N-glycosylation sites individually silenced by mutagenizing N to Q, 1 naturally occurring single-nucleotide polymorphism (SNP) N118S that introduced an N-glycosylation site, and another 10 non-synonymous SNPs located within important functional domains. We observed that syncytin-2 was highly fusogenic and that the mutants had different capacities in merging 293T cells. Of the 21 mutants, N133Q, N312Q, N443Q, C46R (in the CXXC motif) and R417H (in the heptad repeat region and immunosuppressive domain) lost their fusogenicity, whereas N332Q, N118S, T367M (in the fusion peptide), V483I (in the transmembrane domain) and T522M (in the cytoplasmic domain) enhanced the fusogenic activity. We also proved that N133, N146, N177, N220, N241, N247, N312, N332 and N443 were all glycosylated in 293T cells. A co-immunoprecipitation assay showed compromised interaction between mutants N443Q, C46R, T367M, R417H and the receptor MFSD2A, whereas N118S was associated with more receptors. We also sequenced the coding sequence of syncytin-2 in 125 severe pre-eclamptic patients and 272 normal pregnant Chinese women. Surprisingly, only 1 non-synonymous SNP T522M was found and the frequencies of heterozygous carriers were not significantly different. Taken together, our results suggest that N-glycans at residues 133, 312, 332 and 443 of syncytin-2 are required for optimal fusion induction, and that SNPs C46R, N118S, T367M, R417H, V483I and T522M can alter the fusogenic function of syncytin-2.
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Affiliation(s)
- Lina Cui
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China.,b Graduate School of Chinese Academy of Sciences , Beijing , China
| | - Huiying Wang
- c Department of Obstetrics and Gynecology , Beijing Shijitan Hospital , Beijing , China
| | - Xiaoyin Lu
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China.,b Graduate School of Chinese Academy of Sciences , Beijing , China
| | - Rui Wang
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China.,b Graduate School of Chinese Academy of Sciences , Beijing , China
| | - Ru Zheng
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China.,b Graduate School of Chinese Academy of Sciences , Beijing , China
| | - Yue Li
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China
| | - Xiaokui Yang
- d Beijing Obstetrics and Gynecology Hospital, Capital Medical University , Beijing , China
| | - Wen-Tong Jia
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China.,b Graduate School of Chinese Academy of Sciences , Beijing , China
| | - Yangyu Zhao
- e Department of Obstetrics and Gynecology , Peking University Third Hospital , Beijing , China
| | - Yongqing Wang
- e Department of Obstetrics and Gynecology , Peking University Third Hospital , Beijing , China
| | - Haibin Wang
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China
| | - Yan-Ling Wang
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China
| | - Cheng Zhu
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China
| | - Hai-Yan Lin
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China
| | - Hongmei Wang
- a State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing , China
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Shi J, Zhang H, Gong R, Xiao G. Characterization of the fusion core in zebrafish endogenous retroviral envelope protein. Biochem Biophys Res Commun 2015; 460:633-8. [PMID: 25804638 PMCID: PMC7092836 DOI: 10.1016/j.bbrc.2015.03.081] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 03/14/2015] [Indexed: 10/26/2022]
Abstract
Zebrafish endogenous retrovirus (ZFERV) is the unique endogenous retrovirus in zebrafish, as yet, containing intact open reading frames of its envelope protein gene in zebrafish genome. Similarly, several envelope proteins of endogenous retroviruses in human and other mammalian animal genomes (such as syncytin-1 and 2 in human, syncytin-A and B in mouse) were identified and shown to be functional in induction of cell-cell fusion involved in placental development. ZFERV envelope protein (Env) gene appears to be also functional in vivo because it is expressible. After sequence alignment, we found ZFERV Env shares similar structural profiles with syncytin and other type I viral envelopes, especially in the regions of N- and C-terminal heptad repeats (NHR and CHR) which were crucial for membrane fusion. We expressed the regions of N + C protein in the ZFERV Env (residues 459-567, including predicted NHR and CHR) to characterize the fusion core structure. We found N + C protein could form a stable coiled-coil trimer that consists of three helical NHR regions forming a central trimeric core, and three helical CHR regions packing into the grooves on the surface of the central core. The structural characterization of the fusion core revealed the possible mechanism of fusion mediated by ZFERV Env. These results gave comprehensive explanation of how the ancient virus infects the zebrafish and integrates into the genome million years ago, and showed a rational clue for discovery of physiological significance (e.g., medicate cell-cell fusion).
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Affiliation(s)
- Jian Shi
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China; State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, Hubei 430071, China
| | - Huaidong Zhang
- CAS Key Laboratory of Special Pathogens and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, Hubei 430071, China
| | - Rui Gong
- CAS Key Laboratory of Special Pathogens and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, Hubei 430071, China.
| | - Gengfu Xiao
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China; State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, Hubei 430071, China.
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18
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Affiliation(s)
- Benjamin Podbilewicz
- Department of Biology, Technion–Israel Institute of Technology, Haifa 32000, Israel;
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A targeted mutation within the feline leukemia virus (FeLV) envelope protein immunosuppressive domain to improve a canarypox virus-vectored FeLV vaccine. J Virol 2013; 88:992-1001. [PMID: 24198407 DOI: 10.1128/jvi.02234-13] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We previously delineated a highly conserved immunosuppressive (IS) domain within murine and primate retroviral envelope proteins that is critical for virus propagation in vivo. The envelope-mediated immunosuppression was assessed by the ability of the proteins, when expressed by allogeneic tumor cells normally rejected by engrafted mice, to allow these cells to escape, at least transiently, immune rejection. Using this approach, we identified key residues whose mutation (i) specifically abolishes immunosuppressive activity without affecting the "mechanical" function of the envelope protein and (ii) significantly enhances humoral and cellular immune responses elicited against the virus. The objective of this work was to study the immunosuppressive activity of the envelope protein (p15E) of feline leukemia virus (FeLV) and evaluate the effect of its abolition on the efficacy of a vaccine against FeLV. Here we demonstrate that the FeLV envelope protein is immunosuppressive in vivo and that this immunosuppressive activity can be "switched off" by targeted mutation of a specific amino acid. As a result of the introduction of the mutated envelope sequence into a previously well characterized canarypox virus-vectored vaccine (ALVAC-FeLV), the frequency of vaccine-induced FeLV-specific gamma interferon (IFN-γ)-producing cells was increased, whereas conversely, the frequency of vaccine-induced FeLV-specific interleukin-10 (IL-10)-producing cells was reduced. This shift in the IFN-γ/IL-10 response was associated with a higher efficacy of ALVAC-FeLV against FeLV infection. This study demonstrates that FeLV p15E is immunosuppressive in vivo, that the immunosuppressive domain of p15E can modulate the FeLV-specific immune response, and that the efficacy of FeLV vaccines can be enhanced by inhibiting the immunosuppressive activity of the IS domain through an appropriate mutation.
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Crystal structures of beta- and gammaretrovirus fusion proteins reveal a role for electrostatic stapling in viral entry. J Virol 2013; 88:143-53. [PMID: 24131724 DOI: 10.1128/jvi.02023-13] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Membrane fusion is a key step in the life cycle of all envelope viruses, but this process is energetically unfavorable; the transmembrane fusion subunit (TM) of the virion-attached glycoprotein actively catalyzes the membrane merger process. Retroviral glycoproteins are the prototypical system to study pH-independent viral entry. In this study, we determined crystal structures of extramembrane regions of the TMs from Mason-Pfizer monkey virus (MPMV) and xenotropic murine leukemia virus-related virus (XMRV) at 1.7-Å and 2.2-Å resolution, respectively. The structures are comprised of a trimer of hairpins that is characteristic of class I viral fusion proteins and now completes a structural library of retroviral fusion proteins. Our results allowed us to identify a series of intra- and interchain electrostatic interactions in the heptad repeat and chain reversal regions. Mutagenesis reveals that charge-neutralizing salt bridge mutations significantly destabilize the postfusion six-helix bundle and abrogate retroviral infection, demonstrating that electrostatic stapling of the fusion subunit is essential for viral entry. Our data indicate that salt bridges are a major stabilizing force on the MPMV and XMRV retroviral TMs and likely provide the key energetics for viral and host membrane fusion.
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21
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Blinov VM, Krasnov GS, Shargunov AV, Shurdov MA, Zverev VV. Immunosuppressive domains of retroviruses: Cell mechanisms of the effect on the human immune system. Mol Biol 2013. [DOI: 10.1134/s0026893313050026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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23
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Avinoam O, Podbilewicz B. Eukaryotic cell-cell fusion families. CURRENT TOPICS IN MEMBRANES 2012; 68:209-34. [PMID: 21771501 DOI: 10.1016/b978-0-12-385891-7.00009-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Ori Avinoam
- Department of Biology, Technion, Israel Institute of Technology, Haifa, Israel
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24
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Parasites or cohabitants: cruel omnipresent usurpers or creative "éminences grises"? J Parasitol Res 2011; 2011:214174. [PMID: 21785696 PMCID: PMC3140032 DOI: 10.1155/2011/214174] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Accepted: 04/06/2011] [Indexed: 12/31/2022] Open
Abstract
This paper presents many types of interplays between parasites and the host, showing the history of parasites, the effects of parasites on the outcome of wars, invasions, migrations, and on the development of numerous regions of the globe, and the impact of parasitic diseases on the society and on the course of human evolution. It also emphasizes the pressing need to change the look at the parasitism phenomenon, proposing that the term “cohabitant” is more accurate than parasite, because every living being, from bacteria to mammals, is a consortium of living beings in the pangenome. Even the term parasitology should be replaced by cohabitology because there is no parasite alone and host alone: both together compose a new adaptive system: the parasitized-host or the cohabitant-cohabited being. It also suggests switching the old paradigm based on attrition and destruction, to a new one founded on adaptation and living together.
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25
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Lamb D, Schüttelkopf AW, van Aalten DMF, Brighty DW. Charge-surrounded pockets and electrostatic interactions with small ions modulate the activity of retroviral fusion proteins. PLoS Pathog 2011; 7:e1001268. [PMID: 21304939 PMCID: PMC3033372 DOI: 10.1371/journal.ppat.1001268] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Accepted: 12/31/2010] [Indexed: 11/25/2022] Open
Abstract
Refolding of viral class-1 membrane fusion proteins from a native state to a trimer-of-hairpins structure promotes entry of viruses into cells. Here we present the structure of the bovine leukaemia virus transmembrane glycoprotein (TM) and identify a group of asparagine residues at the membrane-distal end of the trimer-of-hairpins that is strikingly conserved among divergent viruses. These asparagines are not essential for surface display of pre-fusogenic envelope. Instead, substitution of these residues dramatically disrupts membrane fusion. Our data indicate that, through electrostatic interactions with a chloride ion, the asparagine residues promote assembly and profoundly stabilize the fusion-active structures that are required for viral envelope-mediated membrane fusion. Moreover, the BLV TM structure also reveals a charge-surrounded hydrophobic pocket on the central coiled coil and interactions with basic residues that cluster around this pocket are critical to membrane fusion and form a target for peptide inhibitors of envelope function. Charge-surrounded pockets and electrostatic interactions with small ions are common among class-1 fusion proteins, suggesting that small molecules that specifically target such motifs should prevent assembly of the trimer-of-hairpins and be of value as therapeutic inhibitors of viral entry. Human T-cell leukaemia virus types-1 (HTLV-1) and bovine leukaemia virus (BLV) are divergent blood borne viruses that cause hematological malignancies in humans and cattle respectively. In common with other enveloped viruses, infection of cells by HTLV-1 and BLV is dependent on the membrane fusion properties of the viral envelope glycoproteins. Here we have solved the crystal structure of the BLV transmembrane glycoprotein, and, through a functional and comparative analysis with HTLV-1, we have identified features that are critical to fusion protein function. In particular, we demonstrate that electrostatic interactions with small ions dramatically stabilize the assembly and fusion-associated forms of the BLV TM, but are not required for the cell surface display of native pre-fusogenic envelope. Moreover, we show that charged residues that border a deep hydrophobic pocket contribute directly to appropriate folding of fusion-active envelope and are critical to membrane fusion. Importantly, the charged residues that border the pocket are key features that determine the specificity and activity of peptide inhibitors of envelope function. Our study demonstrates that charge-surrounded pockets and electrostatic interactions with small ions are significant leitmotifs of diverse class-1 fusion proteins and that these elements represent ideal targets for novel small-molecule inhibitors of viral entry.
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Affiliation(s)
- Daniel Lamb
- The Biomedical Research Institute, College of Medicine, Ninewells Hospital, The University of Dundee, Dundee, United Kingdom
| | - Alexander W. Schüttelkopf
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Daan M. F. van Aalten
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - David W. Brighty
- The Biomedical Research Institute, College of Medicine, Ninewells Hospital, The University of Dundee, Dundee, United Kingdom
- * E-mail:
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26
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Retroviral infection in vivo requires an immune escape virulence factor encrypted in the envelope protein of oncoretroviruses. Proc Natl Acad Sci U S A 2010; 107:3782-7. [PMID: 20142478 DOI: 10.1073/pnas.0913122107] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
We previously delineated a highly conserved immunosuppressive (IS) domain within murine and primate retroviral envelope proteins (Envs). The envelope-mediated immunosuppression was manifested by the ability of the proteins, when expressed by allogeneic tumor cells normally rejected by engrafted mice, to allow these cells to escape, at least transiently, immune rejection. Using this approach, we identified key residues whose mutation specifically abolishes IS activity without affecting the "mechanical" fusogenic function of the entire envelope. Here, we genetically "switched off' the envelope-mediated immunosuppression of an infectious retrovirus, the Friend murine leukemia virus, while preserving mutant envelope infectivity both ex vivo and in vivo, thus allowing us to test the functional importance of envelope-mediated immunosuppression in retrovirus physiology. Remarkably, we show, in vivo, that the non-IS mutant virus displays the same propagation kinetics as its WT counterpart in irradiated immunocompromised mice but that it is rapidly and totally cleared from normal immunocompetent mice, which become fully protected against a challenge with the WT retrovirus. Using cell depletion strategies, we further establish that envelope-mediated immunosuppression enables the retrovirus to escape innate (natural killer cells) and adaptive (CD8 T cells) antiviral effectors. Finally, we show that inactivated mutant virions induce higher humoral and cellular responses than their WT counterparts. In conclusion, our work demonstrates the critical role of Env-induced immunosuppression for retrovirus propagation in vivo and identifies a unique definite target for antiretroviral therapies and vaccine strategies, also characterized in the human T-cell leukemia virus (HTLV) and xenotropic murine leukemia virus-related virus (XMRV) retroviruses, opening unprecedented prospects for the treatment of retroviral diseases.
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27
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Syncytin-2 Plays an Important Role in the Fusion of Human Trophoblast Cells. J Mol Biol 2009; 392:301-18. [DOI: 10.1016/j.jmb.2009.07.025] [Citation(s) in RCA: 126] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2009] [Revised: 06/29/2009] [Accepted: 07/07/2009] [Indexed: 11/22/2022]
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28
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Gasent Blesa J, Candel V. Cell-cell fusion as a potential target in cancer therapy. Ecancermedicalscience 2009; 3:145. [PMID: 22276010 PMCID: PMC3224012 DOI: 10.3332/ecancer.2009.145] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2009] [Indexed: 11/11/2022] Open
Abstract
In the fight against cancer, new and more specific targets are needed. Here, we offer an example of a potential target that has not been widely studied, namely the syncytin protein. Syncytin is expressed mainly in the human placenta and is implicated in placental syncytiotrophoblast cell fusion. Not much is known about the role of syncytin in cancer, but the existing data call for more intense research. Its retroviral origin and particular tissue distribution make syncytin an interesting potential target in cancer therapy.
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Affiliation(s)
- Jm Gasent Blesa
- Hospital General Universitari Marina Alta, Denia, Plana de l'Est no 5, Alacant, Spain
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29
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Guardado-Calvo P, Fox GC, Llamas-Saiz AL, van Raaij MJ. Crystallographic structure of the -helical triple coiled-coil domain of avian reovirus S1133 fibre. J Gen Virol 2009; 90:672-677. [DOI: 10.1099/vir.0.008276-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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30
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Middeldorp JM, Pegtel DM. Multiple roles of LMP1 in Epstein-Barr virus induced immune escape. Semin Cancer Biol 2008; 18:388-96. [PMID: 19013244 DOI: 10.1016/j.semcancer.2008.10.004] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Accepted: 10/16/2008] [Indexed: 12/21/2022]
Abstract
The life cycle of Epstein-Barr virus (EBV) is intriguing in that the virus resides within the immune system and utilizes distinct latency expression programs to establish a persistent infection yet escaping elimination. To achieve this EBV has hijacked cellular signaling pathways to its own benefit, but deregulated viral gene expression can turn into oncogenesis. EBV like many other persistent herpes viruses has evolved ingenious tricks to evade the immune system in part by mimicking host gene function(s). Latent membrane protein 1 (LMP1) mimics CD40 signaling as part of its "normal" biological function and when deregulated, functions as a viral oncogene. LMP1 also affects cell-cell contact, cytokine and chemokine production, Ag presentation and is secreted in the extracellular milieu via immunogenic exosomes. Thus, besides its well-known growth promoting properties LMP1 modulates immune responses. Herein we discuss current knowledge regarding the role of LMP1 in immune evasion of EBV and how this strategy for establishment of persistence contributes to immune escape of EBV+ tumors.
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Affiliation(s)
- J M Middeldorp
- VU University Medical Center, Department of Pathology and Cancer Center Amsterdam, The Netherlands.
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31
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Kjeldbjerg AL, Villesen P, Aagaard L, Pedersen FS. Gene conversion and purifying selection of a placenta-specific ERV-V envelope gene during simian evolution. BMC Evol Biol 2008; 8:266. [PMID: 18826608 PMCID: PMC2567338 DOI: 10.1186/1471-2148-8-266] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2008] [Accepted: 09/30/2008] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND Most human endogenous retroviruses (HERVs) invaded our genome at least 25 million years ago. The majority of the viral genes are degenerated, since no selection preserves them within the genome. However, a few intact and very old HERV genes exist, and likely are beneficial for the host. We here address evolutionary aspects of two HERV-V envelope genes, ENVV1 and ENVV2, located in tandem and containing a long open reading frame. RESULTS The ENVV2 gene is preserved with an intact reading frame during simian evolution, but none of the ENVV genes are found in the prosimian species tested. While we observe many transposon insertions in the gag and pol regions of the ERV-V2 provirus, the ENVV2 genes have escaped transposon crossfire in all species tested. Additional analysis of nucleotide substitutions provides further strong evidence of purifying selection on the ENVV2 gene during primate evolution. The other copy, ENVV1, seems to be involved in gene conversion of the major part of the envelope. Furthermore, ENVV1 and ENVV2 show placenta-specific expression in human and a baboon species. CONCLUSION Our analyses show that ERV-V entered our genome after the split between simian and prosimian primates. Subsequent purifying selection and gene conversion have preserved two copies of the ENVV envelope gene in most species. This is the first case of gene conversion involving long open reading frames in HERVs. Together with the placenta-specific expression of the human and baboon ENVV1 and ENVV2 envelope genes, these data provide strong evidence of a beneficial role for the host.
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Affiliation(s)
- Anders L Kjeldbjerg
- Department of Molecular Biology, University of Aarhus, DK-8000 Aarhus C, Denmark.
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Sapir A, Avinoam O, Podbilewicz B, Chernomordik LV. Viral and developmental cell fusion mechanisms: conservation and divergence. Dev Cell 2008; 14:11-21. [PMID: 18194649 PMCID: PMC3549671 DOI: 10.1016/j.devcel.2007.12.008] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Membrane fusion is a fundamental requirement in numerous developmental, physiological, and pathological processes in eukaryotes. So far, only a limited number of viral and cellular fusogens, proteins that fuse membranes, have been isolated and characterized. Despite the diversity in structures and functions of known fusogens, some common principles of action apply to all fusion reactions. These can serve as guidelines in the search for new fusogens, and may allow the formulation of a cross-species, unified theory to explain divergent and convergent evolutionary principles of membrane fusion.
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Affiliation(s)
- Amir Sapir
- Department of Biology, The Technion, Israel Institute of Technology, Haifa 32000, Israel
| | - Ori Avinoam
- Department of Biology, The Technion, Israel Institute of Technology, Haifa 32000, Israel
| | - Benjamin Podbilewicz
- Department of Biology, The Technion, Israel Institute of Technology, Haifa 32000, Israel
| | - Leonid V. Chernomordik
- Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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33
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Placental syncytins: Genetic disjunction between the fusogenic and immunosuppressive activity of retroviral envelope proteins. Proc Natl Acad Sci U S A 2007; 104:20534-9. [PMID: 18077339 DOI: 10.1073/pnas.0707873105] [Citation(s) in RCA: 219] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have previously demonstrated that the envelope proteins of a murine and primate retrovirus are immunosuppressive in vivo. This property was manifested by the ability of the proteins, when expressed by allogeneic tumor cells normally rejected by engrafted mice, to have the env-expressing cells escape (at least transiently) immune rejection. Here, we analyzed the immunosuppressive activity of the human and murine syncytins. These are envelope genes from endogenous retroviruses independently coopted by ancestral hosts, conserved in evolution, specifically expressed in the placenta, and with a cell-cell fusogenic activity likely contributing to placenta morphogenesis. We show that in both humans and mice, one of the two syncytins (human syncytin-2 and mouse syncytin-B) is immunosuppressive and, rather unexpectedly, the other (human syncytin-1 and mouse syncytin-A) is not (albeit able to induce cell-cell fusion). Delineation of the immunosuppressive domain by deletion analysis, combined with a comparison between immunosuppressive and nonimmunosuppressive sequences, allowed us to derive a mutation rule targeted to specific amino acids, resulting in selective switch from immunosuppressive to nonimmunosuppressive envelope proteins and vice versa. These results unravel a critical function of retroviral envelopes, not necessarily "individually" selected for in the retrovirus endogenization process, albeit "tandemly" conserved in evolution for the syncytin pairs in primates and Muridae. Selective inactivation of immunosuppression, under conditions not affecting fusogenicity, should be important for understanding the role of this function in placental physiology and maternofetal tolerance.
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Peng X, Pan J, Gong R, Liu Y, Kang S, Feng H, Qiu G, Guo D, Tien P, Xiao G. Functional Characterization of Syncytin-A, a Newly Murine Endogenous Virus Envelope Protein. J Biol Chem 2007; 282:381-9. [PMID: 17105734 DOI: 10.1074/jbc.m606353200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Trophoblast fusion in placenta is an important event for preservation of a healthy pregnancy. This process takes place throughout the pregnancy and is crucial for the formation of syncytiotrophoblast layer. Syncytin-1 and syncytin-2 are strong candidate regulators of fusion from retroviral origin. Syncytin-A and syncytin-B are other candidates from retroviral origin in Muridae. The active role of syncytin in driving fusion of trophoblast has been identified, but its fusion mechanism is still unclear. As an intact retroviral envelope protein, syncytin-A shares similar structure profiling with other viral envelope fusion proteins, especially in the regions of N- and C-terminal heptad repeats (NHR and CHR, respectively). In this paper, we showed that SynA 1 + 2 of syncytin-A (residues 445-536, including predicted NHR, CHR, and a natural linker) could form trimer and exhibited significant alpha-helix structure and high thermo-stability. Limited proteolysis result identified a stable protease-resistant core of SynA 1 + 2, which was in good agreement with computational modeling data. NHR and CHR could interact with each other in vitro, too. Different from the previous studies, the disulfide-bonded linker was apparently vital to the stability of fusion core structure. By biological assays, NHR was shown to be inhibitive to cell-cell fusion, with IC(50) value about 5.4 microm, but CHR seemed to have no inhibitory activity even at 50 microm. From both biochemical and functional data, we first gave an explanation how syncytin-A mediated cell fusion. The insight into the mechanism of syncytin-A-mediated cell-cell fusion may provide a crucial clue to placental cytotrophoblast morphogenesis.
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Affiliation(s)
- Xiaoxue Peng
- State Key Laboratory of Virology and Modern Virology Research Centre, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
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Huppertz B, Bartz C, Kokozidou M. Trophoblast fusion: Fusogenic proteins, syncytins and ADAMs, and other prerequisites for syncytial fusion. Micron 2006; 37:509-17. [PMID: 16497505 DOI: 10.1016/j.micron.2005.12.011] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2005] [Accepted: 12/27/2005] [Indexed: 11/26/2022]
Abstract
Trophoblast fusion in the placenta is an event of major importance for the preservation of a healthy pregnancy. This process takes place throughout pregnancy and is crucial for the maintenance of the syncytiotrophoblast layer, the direct border between maternal blood and fetal tissues. Different regulatory proteins have been reported that are involved in trophoblast fusion. Syncytin-1 is a candidate regulator of fusion together with its receptors ASCT2 (RDR) and ASCT1. Little is known about the receptor properties and the interactions between receptor and ligand. Syncytin-2 or HERV-FRD is another strong candidate also of retroviral origin; while its actual function still remains to be explored. ADAM12 has been proposed to be a candidate regulator of trophoblast fusion since it is known to be involved in myoblast fusion, a process with a variety of similarities to trophoblast fusion. Beside these regulatory proteins, there is the necessity of a flip of phosphatidylserine from the inner to the outer leaflet of the plasma membranes of the fusing cells. Moreover, appropriate events of the early and still reversible stages of the apoptosis cascade are indispensable for trophoblast fusion. In this review, we present some details on the above events and proteins with their most important properties that could explain their roles in trophoblast fusion.
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Affiliation(s)
- Berthold Huppertz
- Department of Cell Biology, Histology and Embryology, Medical University Graz, Harrachgasse 21, 8010 Graz, Austria.
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