1
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Sagan SM, Weber SC. Let's phase it: viruses are master architects of biomolecular condensates. Trends Biochem Sci 2023; 48:229-243. [PMID: 36272892 DOI: 10.1016/j.tibs.2022.09.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2022] [Revised: 09/23/2022] [Accepted: 09/26/2022] [Indexed: 11/15/2022]
Abstract
Viruses compartmentalize their replication and assembly machinery to both evade detection and concentrate the viral proteins and nucleic acids necessary for genome replication and virion production. Accumulating evidence suggests that diverse RNA and DNA viruses form replication organelles and nucleocapsid assembly sites using phase separation. In general, the biogenesis of these compartments is regulated by two types of viral protein, collectively known as antiterminators and nucleocapsid proteins, respectively. Herein, we discuss how RNA viruses establish replication organelles and nucleocapsid assembly sites, and the evidence that these compartments form through phase separation. While this review focuses on RNA viruses, accumulating evidence suggests that all viruses rely on phase separation and form biomolecular condensates important for completing the infectious cycle.
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Affiliation(s)
- Selena M Sagan
- Department of Microbiology & Immunology, McGill University, Montreal, QC, Canada; Department of Biochemistry, McGill University, Montreal, QC, Canada.
| | - Stephanie C Weber
- Department of Biology, McGill University, Montreal, QC, Canada; Department of Physics, McGill University, Montreal, QC, Canada
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2
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Activity, Template Preference, and Compatibility of Components of RNA Replicase of Eastern Equine Encephalitis Virus. J Virol 2023; 97:e0136822. [PMID: 36533950 PMCID: PMC9888243 DOI: 10.1128/jvi.01368-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Eastern equine encephalitis virus (EEEV) usually cycles between Culiseta melanura mosquitoes and birds; however, it can also infect humans. EEEV has a positive-sense RNA genome that, in infected cells, serves as an mRNA for the P1234 polyprotein. P1234 undergoes a series of precise cleavage events producing four nonstructural proteins (nsP1-4) representing subunits of the RNA replicase. Here, we report the construction and properties of a trans-replicase for EEEV. The template RNA of EEEV was shown to be replicated by replicases of diverse alphaviruses. The EEEV replicase, on the other hand, demonstrated limited ability in replicating template RNAs originating from alphaviruses of the Semliki Forest virus complex. The replicase of EEEV was also successfully reconstructed from P123 and nsP4 components. The ability of EEEV P123 to form functional RNA replicases with heterologous nsP4s was more efficient using EEEV template RNA than heterologous alphavirus template RNA. This finding indicates that unlike with previously studied Semliki Forest complex alphaviruses, P123 and/or its processing products have a leading role in EEEV template RNA recognition. Infection of HEK293T cells harboring the EEEV template RNA with EEEV or Western equine encephalitis virus prominently activated expression of a reporter encoded in the template RNA; the effect was much smaller for infection with other alphaviruses and not detectable upon flavivirus infection. At the same time, EEEV infection resulted only in a limited activation of the template RNA of chikungunya virus. Thus, cells harboring reporter-carrying template RNAs can be used as sensitive and selective biosensors for different alphaviruses. IMPORTANCE Infection of EEEV in humans can cause serious neurologic disease with an approximately 30% fatality rate. Although human infections are rare, a record-breaking number was documented in 2019. The replication of EEEV has a unique requirement for host factors but is poorly studied, partly because the virus requires biosafety level 3 facilities which can limit the scope of experiments; at the same time, these studies are crucial for developing antiviral approaches. The EEEV trans-replicase developed here contributes significantly to research on EEEV, providing a safe and versatile tool for studying the virus RNA replication. Using this system, the compatibility of EEEV replicase components with counterparts from other alphaviruses was analyzed. The obtained data can be used to develop unique biosensors that provide alternative methods for detection, identification, quantitation, and neutralization of viable alphaviruses that are compatible with high throughput, semiautomated approaches.
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3
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Mendonça DC, Reis EVS, Arias NEC, Valencia HJ, Bonjardim CA. A study of the MAYV replication cycle: Correlation between the kinetics of viral multiplication and viral morphogenesis. Virus Res 2023; 323:199002. [PMID: 36370917 PMCID: PMC10194297 DOI: 10.1016/j.virusres.2022.199002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 10/24/2022] [Accepted: 11/08/2022] [Indexed: 11/11/2022]
Abstract
Mayaro virus (MAYV) is mainly found in Central and South America and causes a febrile illness followed by debilitating arthritis and arthralgia similar to chikungunya virus (CHIKV). Infection leads to long-term sequelae with a direct impact on the patient's productive capacity, resulting in economic losses. Mayaro fever is a neglected disease due to the limited epidemiological data. In Brazil, it is considered a potential public health risk with the number of cases increasing every year. Most of our knowledge about MAYV biology is inferred from data obtained from other alphaviruses as well as more recent studies on MAYV. Here, we analyzed the kinetics of viral replication through standard growth curves, quantification of intracellular and extracellular particles, and RNA quantification. We compared transmission electron microscopy data during different stages of infection. This approach allowed us to establish a chronological order of events during MAYV replication and its respective timepoints including cell entry through clathrin-mediated endocytosis occurring at 15-30 min, genome replication at 2-3 h, morphogenesis at 4 hpi, and release at 4-6 hpi. We also present evidence of uncharacterized events such as ribosome reorganization as well as clusters of early viral precursors and release through exocytosis in giant forms. Our work sheds new and specific light on the MAYV replication cycle and may contribute to future studies on the field.
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Affiliation(s)
- Diogo C Mendonça
- Grupo de Transdução de Sinal, Laboratório de Vírus, Department of Microbiology, Institute of Biological Sciences, Universidade Federal de Minas Gerais., 31270-901, Avenida Antonio Carlos, 6627, Belo Horizonte, Minas Gerais, Brazil.
| | - Erik V S Reis
- Grupo de Transdução de Sinal, Laboratório de Vírus, Department of Microbiology, Institute of Biological Sciences, Universidade Federal de Minas Gerais., 31270-901, Avenida Antonio Carlos, 6627, Belo Horizonte, Minas Gerais, Brazil
| | - Nídia E C Arias
- Grupo de Transdução de Sinal, Laboratório de Vírus, Department of Microbiology, Institute of Biological Sciences, Universidade Federal de Minas Gerais., 31270-901, Avenida Antonio Carlos, 6627, Belo Horizonte, Minas Gerais, Brazil
| | - Hugo J Valencia
- Grupo de Transdução de Sinal, Laboratório de Vírus, Department of Microbiology, Institute of Biological Sciences, Universidade Federal de Minas Gerais., 31270-901, Avenida Antonio Carlos, 6627, Belo Horizonte, Minas Gerais, Brazil
| | - Cláudio A Bonjardim
- Grupo de Transdução de Sinal, Laboratório de Vírus, Department of Microbiology, Institute of Biological Sciences, Universidade Federal de Minas Gerais., 31270-901, Avenida Antonio Carlos, 6627, Belo Horizonte, Minas Gerais, Brazil
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4
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Skidmore AM, Bradfute SB. The life cycle of the alphaviruses: From an antiviral perspective. Antiviral Res 2023; 209:105476. [PMID: 36436722 PMCID: PMC9840710 DOI: 10.1016/j.antiviral.2022.105476] [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: 06/20/2022] [Revised: 11/18/2022] [Accepted: 11/21/2022] [Indexed: 11/27/2022]
Abstract
The alphaviruses are a widely distributed group of positive-sense, single stranded, RNA viruses. These viruses are largely arthropod-borne and can be found on all populated continents. These viruses cause significant human disease, and recently have begun to spread into new populations, such as the expansion of Chikungunya virus into southern Europe and the Caribbean, where it has established itself as endemic. The study of alphaviruses is an active and expanding field, due to their impacts on human health, their effects on agriculture, and the threat that some pose as potential agents of biological warfare and terrorism. In this systematic review we will summarize both historic knowledge in the field as well as recently published data that has potential to shift current theories in how alphaviruses are able to function. This review is comprehensive, covering all parts of the alphaviral life cycle as well as a brief overview of their pathology and the current state of research in regards to vaccines and therapeutics for alphaviral disease.
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Affiliation(s)
- Andrew M Skidmore
- Center for Global Health, Department of Internal Medicine, University of New Mexico Health Sciences Center, 915 Camino de Salud, IDTC Room 3245, Albuquerque, NM, 87131, USA.
| | - Steven B Bradfute
- Center for Global Health, Department of Internal Medicine, University of New Mexico Health Sciences Center, 915 Camino de Salud, IDTC Room 3330A, Albuquerque, NM, 87131, USA.
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5
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Neufeldt CJ, Cortese M. Membrane architects: how positive-strand RNA viruses restructure the cell. J Gen Virol 2022; 103. [PMID: 35976091 DOI: 10.1099/jgv.0.001773] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Virus infection is a process that requires combined contributions from both virus and host factors. For this process to be efficient within the crowded host environment, viruses have evolved ways to manipulate and reorganize host structures to produce cellular microenvironments. Positive-strand RNA virus replication and assembly occurs in association with cytoplasmic membranes, causing a reorganization of these membranes to create microenvironments that support viral processes. Similarities between virus-induced membrane domains and cellular organelles have led to the description of these structures as virus replication organelles (vRO). Electron microscopy analysis of vROs in positive-strand RNA virus infected cells has revealed surprising morphological similarities between genetically diverse virus species. For all positive-strand RNA viruses, vROs can be categorized into two groups: those that make invaginations into the cellular membranes (In-vRO), and those that cause the production of protrusions from cellular membranes (Pr-vRO), most often in the form of double membrane vesicles (DMVs). In this review, we will discuss the current knowledge on the structure and biogenesis of these two different vRO classes as well as comparing morphology and function of vROs between various positive-strand RNA viruses. Finally, we will discuss recent studies describing pharmaceutical intervention in vRO formation as an avenue to control virus infection.
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Affiliation(s)
- Christopher John Neufeldt
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Mirko Cortese
- Telethon Institute of Genetics and Medicine, Pozzuoli, Italy
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6
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Cherkashchenko L, Rausalu K, Basu S, Alphey L, Merits A. Expression of Alphavirus Nonstructural Protein 2 (nsP2) in Mosquito Cells Inhibits Viral RNA Replication in Both a Protease Activity-Dependent and -Independent Manner. Viruses 2022; 14:v14061327. [PMID: 35746799 PMCID: PMC9228716 DOI: 10.3390/v14061327] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 06/12/2022] [Accepted: 06/15/2022] [Indexed: 01/02/2023] Open
Abstract
Alphaviruses are positive-strand RNA viruses, mostly being mosquito-transmitted. Cells infected by an alphavirus become resistant to superinfection due to a block that occurs at the level of RNA replication. Alphavirus replication proteins, called nsP1-4, are produced from nonstructural polyprotein precursors, processed by the protease activity of nsP2. Trans-replicase systems and replicon vectors were used to study effects of nsP2 of chikungunya virus and Sindbis virus on alphavirus RNA replication in mosquito cells. Co-expressed wild-type nsP2 reduced RNA replicase activity of homologous virus; this effect was reduced but typically not abolished by mutation in the protease active site of nsP2. Mutations in the replicase polyprotein that blocked its cleavage by nsP2 reduced the negative effect of nsP2 co-expression, confirming that nsP2-mediated inhibition of RNA replicase activity is largely due to nsP2-mediated processing of the nonstructural polyprotein. Co-expression of nsP2 also suppressed the activity of replicases of heterologous alphaviruses. Thus, the presence of nsP2 inhibits formation and activity of alphavirus RNA replicase in protease activity-dependent and -independent manners. This knowledge improves our understanding about mechanisms of superinfection exclusion for alphaviruses and may aid the development of anti-alphavirus approaches.
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Affiliation(s)
- Liubov Cherkashchenko
- Institute of Technology, University of Tartu, Nooruse 1, 50411 Tartu, Estonia; (L.C.); (K.R.)
| | - Kai Rausalu
- Institute of Technology, University of Tartu, Nooruse 1, 50411 Tartu, Estonia; (L.C.); (K.R.)
| | - Sanjay Basu
- The Pirbright Institute, Ash Road, Pirbright GU24 ONF, UK; (S.B.); (L.A.)
| | - Luke Alphey
- The Pirbright Institute, Ash Road, Pirbright GU24 ONF, UK; (S.B.); (L.A.)
| | - Andres Merits
- Institute of Technology, University of Tartu, Nooruse 1, 50411 Tartu, Estonia; (L.C.); (K.R.)
- Correspondence:
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7
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Qin S, Tang X, Chen Y, Chen K, Fan N, Xiao W, Zheng Q, Li G, Teng Y, Wu M, Song X. mRNA-based therapeutics: powerful and versatile tools to combat diseases. Signal Transduct Target Ther 2022; 7:166. [PMID: 35597779 PMCID: PMC9123296 DOI: 10.1038/s41392-022-01007-w] [Citation(s) in RCA: 166] [Impact Index Per Article: 83.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/04/2022] [Accepted: 04/19/2022] [Indexed: 02/06/2023] Open
Abstract
The therapeutic use of messenger RNA (mRNA) has fueled great hope to combat a wide range of incurable diseases. Recent rapid advances in biotechnology and molecular medicine have enabled the production of almost any functional protein/peptide in the human body by introducing mRNA as a vaccine or therapeutic agent. This represents a rising precision medicine field with great promise for preventing and treating many intractable or genetic diseases. In addition, in vitro transcribed mRNA has achieved programmed production, which is more effective, faster in design and production, as well as more flexible and cost-effective than conventional approaches that may offer. Based on these extraordinary advantages, mRNA vaccines have the characteristics of the swiftest response to large-scale outbreaks of infectious diseases, such as the currently devastating pandemic COVID-19. It has always been the scientists’ desire to improve the stability, immunogenicity, translation efficiency, and delivery system to achieve efficient and safe delivery of mRNA. Excitingly, these scientific dreams have gradually been realized with the rapid, amazing achievements of molecular biology, RNA technology, vaccinology, and nanotechnology. In this review, we comprehensively describe mRNA-based therapeutics, including their principles, manufacture, application, effects, and shortcomings. We also highlight the importance of mRNA optimization and delivery systems in successful mRNA therapeutics and discuss the key challenges and opportunities in developing these tools into powerful and versatile tools to combat many genetic, infectious, cancer, and other refractory diseases.
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Affiliation(s)
- Shugang Qin
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Xiaoshan Tang
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Yuting Chen
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Kepan Chen
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Na Fan
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Wen Xiao
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Qian Zheng
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Guohong Li
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Yuqing Teng
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China
| | - Min Wu
- Department of Biomedical Sciences, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND, 58203, USA
| | - Xiangrong Song
- Department of Critical Care Medicine, Frontiers Science Center for Disease-related Molecular Network, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China.
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8
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Tan YB, Lello LS, Liu X, Law YS, Kang C, Lescar J, Zheng J, Merits A, Luo D. Crystal structures of alphavirus nonstructural protein 4 (nsP4) reveal an intrinsically dynamic RNA-dependent RNA polymerase fold. Nucleic Acids Res 2022; 50:1000-1016. [PMID: 35037043 PMCID: PMC8789068 DOI: 10.1093/nar/gkab1302] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 12/14/2021] [Accepted: 12/23/2021] [Indexed: 11/12/2022] Open
Abstract
Alphaviruses such as Ross River virus (RRV), chikungunya virus (CHIKV), Sindbis virus (SINV), and Venezuelan equine encephalitis virus (VEEV) are mosquito-borne pathogens that can cause arthritis or encephalitis diseases. Nonstructural protein 4 (nsP4) of alphaviruses possesses RNA-dependent RNA polymerase (RdRp) activity essential for viral RNA replication. No 3D structure has been available for nsP4 of any alphaviruses despite its importance for understanding alphaviral RNA replication and for the design of antiviral drugs. Here, we report crystal structures of the RdRp domain of nsP4 from both RRV and SINV determined at resolutions of 2.6 Å and 1.9 Å. The structure of the alphavirus RdRp domain appears most closely related to RdRps from pestiviruses, noroviruses, and picornaviruses. Hydrogen-deuterium exchange mass spectrometry (HDX-MS) and nuclear magnetic resonance (NMR) methods showed that in solution, nsP4 is highly dynamic with an intrinsically disordered N-terminal domain. Both full-length nsP4 and the RdRp domain were capable to catalyze RNA polymerization. Structure-guided mutagenesis using a trans-replicase system identified nsP4 regions critical for viral RNA replication.
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Affiliation(s)
- Yaw Bia Tan
- Lee Kong Chian School of Medicine, Nanyang Technological University, 59 Nanyang Drive, Singapore 636921.,NTU Institute of Structural Biology, Nanyang Technological University, 59 Nanyang Drive, Singapore 636921
| | - Laura Sandra Lello
- University of Tartu, Institute of Technology, Nooruse 1, 50411 Tartu, Estonia
| | - Xin Liu
- Shanghai Institute of Materia Medica, China Academy of Sciences, 555 Zu Chong Zhi Road, Zhang Jiang Hi-Tech Park, Pudong, Shanghai, China
| | - Yee-Song Law
- Lee Kong Chian School of Medicine, Nanyang Technological University, 59 Nanyang Drive, Singapore 636921.,NTU Institute of Structural Biology, Nanyang Technological University, 59 Nanyang Drive, Singapore 636921
| | - Congbao Kang
- Experimental Drug Development Centre, Agency for Science, Technology and Research (A*STAR), 10 Biopolis Rd, #05-01/06 Chromos, Singapore138670
| | - Julien Lescar
- NTU Institute of Structural Biology, Nanyang Technological University, 59 Nanyang Drive, Singapore 636921.,School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore
| | - Jie Zheng
- Shanghai Institute of Materia Medica, China Academy of Sciences, 555 Zu Chong Zhi Road, Zhang Jiang Hi-Tech Park, Pudong, Shanghai, China
| | - Andres Merits
- University of Tartu, Institute of Technology, Nooruse 1, 50411 Tartu, Estonia
| | - Dahai Luo
- Lee Kong Chian School of Medicine, Nanyang Technological University, 59 Nanyang Drive, Singapore 636921.,NTU Institute of Structural Biology, Nanyang Technological University, 59 Nanyang Drive, Singapore 636921.,School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore
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9
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Abstract
The chikungunya virus has spread globally with a remarkably high attack rate. Infection causes arthralgic sequelae that can last for years. Nevertheless, there are no specific drugs or vaccines to contain the virus. Understanding the biology of the virus, such as its replication cycle, is a powerful tool to identify new drugs and comprehend virus-host interactions. Even though the chikungunya virus has been known for a long time (first described in 1952), many aspects of the replication cycle remain unclear. Furthermore, part of the cycle is based on observations of other alphaviruses. In this study, we used electron and scanning microscopy, as well as biological assays, to analyze and investigate the stages of the chikungunya virus replication cycle. Based on our data, we found other infection cellular activities than those usually described for the chikungunya virus replication cycle, i.e. we show particles enveloping intracellularly without budding in a membrane-delimited morphogenesis area; and we also observed virion release by membrane protrusions. Our work provides novel details regarding the biology of chikungunya virus and fills gaps in our knowledge of its replication cycle. These findings may contribute to a better understanding of virus-host interactions and support the development of antivirals. IMPORTANCE The understanding of virus biology is essential to containing virus dissemination, and exploring the virus replication cycle is a powerful tool to do this. There are many points in the biology of the chikungunya virus that need to be clarified, especially regarding its replication cycle. Our incomplete understanding of chikungunya virus infection stages is based on studies with other alphaviruses. We systematized the chikungunya virus replication cycle using microscopic imaging in the order of infection stages: entry, replication, protein synthesis, assembly/morphogenesis, and release. The imaging evidence shows novel points in the replication cycle of enveloping without budding, as well as particle release by cell membrane protrusion.
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10
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Abstract
Alphaviruses are positive-strand RNA viruses, typically transmitted by mosquitoes between vertebrate hosts. They encode four essential replication proteins, the non-structural proteins nsP1-4, which possess the enzymatic activities of RNA capping, RNA helicase, site-specific protease, ADP-ribosyl removal and RNA polymerase. Alphaviruses have been key models in the study of membrane-associated RNA replication, which is a conserved feature among the positive-strand RNA viruses of animals and plants. We review new structural and functional information on the nsPs and their interaction with host proteins and membranes, as well as with viral RNA sequences. The dodecameric ring structure of nsP1 is likely to be one of the evolutionary innovations that facilitated the success of the progenitors of current positive-strand RNA viruses.
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Affiliation(s)
- Tero Ahola
- Department of Microbiology, Faculty of Agriculture and Forestry, University of Helsinki, Helsinki, Finland
| | - Gerald McInerney
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden
| | - Andres Merits
- Institute of Technology, University of Tartu, Tartu, Estonia.
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11
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Precursors of Viral Proteases as Distinct Drug Targets. Viruses 2021; 13:v13101981. [PMID: 34696411 PMCID: PMC8537868 DOI: 10.3390/v13101981] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 09/25/2021] [Accepted: 09/28/2021] [Indexed: 12/16/2022] Open
Abstract
Viral proteases are indispensable for successful virion maturation, thus making them a prominent drug target. Their enzyme activity is tightly spatiotemporally regulated by expression in the precursor form with little or no activity, followed by activation via autoprocessing. These cleavage events are frequently triggered upon transportation to a specific compartment inside the host cell. Typically, precursor oligomerization or the presence of a co-factor is needed for activation. A detailed understanding of these mechanisms will allow ligands with non-canonical mechanisms of action to be designed, which would specifically modulate the initial irreversible steps of viral protease autoactivation. Binding sites exclusive to the precursor, including binding sites beyond the protease domain, can be exploited. Both inhibition and up-regulation of the proteolytic activity of viral proteases can be detrimental for the virus. All these possibilities are discussed using examples of medically relevant viruses including herpesviruses, adenoviruses, retroviruses, picornaviruses, caliciviruses, togaviruses, flaviviruses, and coronaviruses.
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12
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Abstract
Alphaviruses have positive-strand RNA genomes containing two open reading frames (ORFs). The first ORF encodes the nonstructural (ns) polyproteins P123 and P1234 that act as precursors for the subunits of the viral RNA replicase (nsP1 to nsP4). Processing of P1234 leads to the formation of a negative-strand replicase consisting of nsP4 (RNA polymerase) and P123 components. Subsequent processing of P123 results in a positive-strand replicase. The second ORF encoding the structural proteins is expressed via the synthesis of a subgenomic RNA. Alphavirus replicase is capable of using template RNAs that contain essential cis-active sequences. Here, we demonstrate that the replicases of nine alphaviruses, expressed in the form of separate P123 and nsP4 components, are active. Their activity depends on the abundance of nsP4. The match of nsP4 to its template strongly influences efficient subgenomic RNA synthesis. nsP4 of Barmah Forest virus (BFV) formed a functional replicase only with matching P123, while nsP4s of other alphaviruses were compatible also with several heterologous P123s. The P123 components of Venezuelan equine encephalitis virus and Sindbis virus (SINV) required matching nsP4s, while P123 of other viruses could form active replicases with different nsP4s. Chimeras of Semliki Forest virus, harboring the nsP4 of chikungunya virus, Ross River virus, BFV, or SINV were viable. In contrast, chimeras of SINV, harboring an nsP4 from different alphaviruses, exhibited a temperature-sensitive phenotype. These findings highlight the possibility for formation of new alphaviruses via recombination events and provide a novel approach for the development of attenuated chimeric viruses for vaccination strategies. IMPORTANCE A key element of every virus with an RNA genome is the RNA replicase. Understanding the principles of RNA replicase formation and functioning is therefore crucial for understanding and responding to the emergence of new viruses. Reconstruction of the replicases of nine alphaviruses from nsP4 and P123 polyproteins revealed that the nsP4 of the majority of alphaviruses, including the mosquito-specific Eilat virus, could form a functional replicase with P123 originating from a different virus, and the corresponding chimeric viruses were replication-competent. nsP4 also had an evident role in determining the template RNA preference and the efficiency of RNA synthesis. The revealed broad picture of the compatibility of the replicase components of alphaviruses is important for understanding the formation and functioning of the alphavirus RNA replicase and highlights the possibilities for recombination between different alphavirus species.
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13
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Teppor M, Žusinaite E, Karo-Astover L, Omler A, Rausalu K, Lulla V, Lulla A, Merits A. Semliki Forest Virus Chimeras with Functional Replicase Modules from Related Alphaviruses Survive by Adaptive Mutations in Functionally Important Hot Spots. J Virol 2021; 95:e0097321. [PMID: 34319778 PMCID: PMC8475518 DOI: 10.1128/jvi.00973-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 07/19/2021] [Indexed: 11/20/2022] Open
Abstract
Alphaviruses (family Togaviridae) include both human pathogens such as chikungunya virus (CHIKV) and Sindbis virus (SINV) and model viruses such as Semliki Forest virus (SFV). The alphavirus positive-strand RNA genome is translated into nonstructural (ns) polyprotein(s) that are precursors for four nonstructural proteins (nsPs). The three-dimensional structures of nsP2 and the N-terminal 2/3 of nsP3 reveal that these proteins consist of several domains. Cleavage of the ns-polyprotein is performed by the strictly regulated protease activity of the nsP2 region. Processing results in the formation of a replicase complex that can be considered a network of functional modules. These modules work cooperatively and should perform the same task for each alphavirus. To investigate functional interactions between replicase components, we generated chimeras using the SFV genome as a backbone. The functional modules corresponding to different parts of nsP2 and nsP3 were swapped with their counterparts from CHIKV and SINV. Although some chimeras were nonfunctional, viruses harboring the CHIKV N-terminal domain of nsP2 or any domain of nsP3 were viable. Viruses harboring the protease part of nsP2, the full-length nsP2 of CHIKV, or the nsP3 macrodomain of SINV required adaptive mutations for functionality. Seven mutations that considerably improved the infectivity of the corresponding chimeric genomes affected functionally important hot spots recurrently highlighted in previous alphavirus studies. These data indicate that alphaviruses utilize a rather limited set of strategies to survive and adapt. Furthermore, functional analysis revealed that the disturbance of processing was the main defect resulting from chimeric alterations within the ns-polyprotein. IMPORTANCE Alphaviruses cause debilitating symptoms and have caused massive outbreaks. There are currently no approved antivirals or vaccines for treating these infections. Understanding the functions of alphavirus replicase proteins (nsPs) provides valuable information for both antiviral drug and vaccine development. The nsPs of all alphaviruses consist of similar functional modules; however, to what extent these are independent in functionality and thus interchangeable among homologous viruses is largely unknown. Homologous domain swapping was used to study the functioning of modules from nsP2 and nsP3 of other alphaviruses in the context of Semliki Forest virus. Most of the introduced substitutions resulted in defects in the processing of replicase precursors that were typically compensated by adaptive mutations that mapped to determinants of polyprotein processing. Understanding the principles of virus survival strategies and identifying hot spot mutations that permit virus adaptation highlight a route to the rapid development of attenuated viruses as potential live vaccine candidates.
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Affiliation(s)
- Mona Teppor
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Eva Žusinaite
- Institute of Technology, University of Tartu, Tartu, Estonia
| | | | - Ailar Omler
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Kai Rausalu
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Valeria Lulla
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Aleksei Lulla
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Andres Merits
- Institute of Technology, University of Tartu, Tartu, Estonia
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Elmasri Z, Nasal BL, Jose J. Alphavirus-Induced Membrane Rearrangements during Replication, Assembly, and Budding. Pathogens 2021; 10:984. [PMID: 34451448 PMCID: PMC8399458 DOI: 10.3390/pathogens10080984] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 07/30/2021] [Accepted: 08/02/2021] [Indexed: 01/01/2023] Open
Abstract
Alphaviruses are arthropod-borne viruses mainly transmitted by hematophagous insects that cause moderate to fatal disease in humans and other animals. Currently, there are no approved vaccines or antivirals to mitigate alphavirus infections. In this review, we summarize the current knowledge of alphavirus-induced structures and their functions in infected cells. Throughout their lifecycle, alphaviruses induce several structural modifications, including replication spherules, type I and type II cytopathic vacuoles, and filopodial extensions. Type I cytopathic vacuoles are replication-induced structures containing replication spherules that are sites of RNA replication on the endosomal and lysosomal limiting membrane. Type II cytopathic vacuoles are assembly induced structures that originate from the Golgi apparatus. Filopodial extensions are induced at the plasma membrane and are involved in budding and cell-to-cell transport of virions. This review provides an overview of the viral and host factors involved in the biogenesis and function of these virus-induced structures. Understanding virus-host interactions in infected cells will lead to the identification of new targets for antiviral discovery.
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Affiliation(s)
- Zeinab Elmasri
- Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA;
- Department of Biochemistry & Molecular Biology, Eberly College of Science, The Pennsylvania State University, University Park, PA 16802, USA;
| | - Benjamin L. Nasal
- Department of Biochemistry & Molecular Biology, Eberly College of Science, The Pennsylvania State University, University Park, PA 16802, USA;
| | - Joyce Jose
- Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA;
- Department of Biochemistry & Molecular Biology, Eberly College of Science, The Pennsylvania State University, University Park, PA 16802, USA;
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15
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Kril V, Aïqui-Reboul-Paviet O, Briant L, Amara A. New Insights into Chikungunya Virus Infection and Pathogenesis. Annu Rev Virol 2021; 8:327-347. [PMID: 34255544 DOI: 10.1146/annurev-virology-091919-102021] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Chikungunya virus (CHIKV) is a re-emerging mosquito-borne alphavirus responsible for major outbreaks of disease since 2004 in the Indian Ocean islands, South east Asia, and the Americas. CHIKV causes debilitating musculoskeletal disorders in humans that are characterized by fever, rash, polyarthralgia, and myalgia. The disease is often self-limiting and nonlethal; however, some patients experience atypical or severe clinical manifestations, as well as a chronic rheumatic syndrome. Unfortunately, no efficient antivirals against CHIKV infection are available so far, highlighting the importance of deepening our knowledge of CHIKV host cell interactions and viral replication strategies. In this review, we discuss recent breakthroughs in the molecular mechanisms that regulate CHIKV infection and lay down the foundations to understand viral pathogenesis. We describe the role of the recently identified host factors co-opted by the virus for infection and pathogenesis, and emphasize the importance of CHIKV nonstructural proteins in both replication complex assembly and host immune response evasion. Expected final online publication date for the Annual Review of Virology, Volume 8 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Vasiliya Kril
- Biology of Emerging Virus Team, INSERM U944, CNRS UMR 7212, Institut de Recherche Saint-Louis, Université de Paris, Hôpital Saint-Louis, 75010 Paris, France;
| | - Olivier Aïqui-Reboul-Paviet
- RNA Viruses and Metabolism Team, CNRS UMR 9004, Institut de Recherche en Infectiologie de Montpellier, University of Montpellier, 34293 Montpellier, France;
| | - Laurence Briant
- RNA Viruses and Metabolism Team, CNRS UMR 9004, Institut de Recherche en Infectiologie de Montpellier, University of Montpellier, 34293 Montpellier, France;
| | - Ali Amara
- Biology of Emerging Virus Team, INSERM U944, CNRS UMR 7212, Institut de Recherche Saint-Louis, Université de Paris, Hôpital Saint-Louis, 75010 Paris, France;
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16
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Zhang K, Law YS, Law MCY, Tan YB, Wirawan M, Luo D. Structural insights into viral RNA capping and plasma membrane targeting by Chikungunya virus nonstructural protein 1. Cell Host Microbe 2021; 29:757-764.e3. [DOI: 10.1016/j.chom.2021.02.018] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 02/10/2021] [Accepted: 02/22/2021] [Indexed: 01/30/2023]
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Phosphorylation Sites in the Hypervariable Domain in Chikungunya Virus nsP3 Are Crucial for Viral Replication. J Virol 2021; 95:JVI.02276-20. [PMID: 33568506 DOI: 10.1128/jvi.02276-20] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Accepted: 01/30/2021] [Indexed: 01/26/2023] Open
Abstract
Chikungunya virus (CHIKV, family Togaviridae) is a mosquito-transmitted alphavirus. The positive-sense RNA genome of CHIKV encodes four nonstructural proteins (nsP1 to nsP4) that are virus-specific subunits of the RNA replicase. Among nsP functions, those of nsP3 are the least understood. The C-terminal hypervariable domain (HVD) in nsP3 is disordered and serves as a platform for interactions with multiple host proteins. For Sindbis virus (SINV) and Semliki Forest virus (SFV), the nsP3 HVD has been shown to be phosphorylated. Deletion of phosphorylated regions has a mild effect on the growth of SFV and SINV in vertebrate cells. Using radiolabeling, we demonstrated that nsP3 in CHIKV and o'nyong-nyong virus is also phosphorylated. We showed that the phosphorylated residues in CHIKV nsP3 are not clustered at the beginning of the HVD. The substitution of 20 Ser/Thr residues located in the N-terminal half of the HVD or 26 Ser/Thr residues located in its C-terminal half with Ala residues reduced the activity of the CHIKV replicase and the infectivity of CHIKV in mammalian cells. Furthermore, the substitution of all 46 potentially phosphorylated residues resulted in the complete loss of viral RNA synthesis and infectivity. The mutations did not affect the interaction of the HVD in nsP3 with the host G3BP1 protein; interactions with CD2AP, BIN1, and FHL1 proteins were significantly reduced but not abolished. Thus, CHIKV differs from SFV and SINV both in the location of the phosphorylated residues in the HVD in nsP3 and, significantly, in their effect on replicase activity and virus infectivity.IMPORTANCE CHIKV outbreaks have affected millions of people, creating a need for the development of antiviral approaches. nsP3 is a component of the CHIKV RNA replicase and is involved in interactions with host proteins and signaling cascades. Phosphorylation of the HVD in nsP3 is important for the virulent alphavirus phenotype. Here, we demonstrate that nsP3 in CHIKV is phosphorylated and that the phosphorylation sites in the HVD are distributed in a unique pattern. Furthermore, the abrogation of some of the phosphorylation sites results in the attenuation of CHIKV, while abolishing all the phosphorylation sites completely blocked its replicase activity. Thus, the phosphorylation of nsP3 and/or the phosphorylation sites in nsP3 have a major impact on CHIKV infectivity. Therefore, they represent promising targets for antiviral compounds and CHIKV attenuation. In addition, this new information offers valuable insight into the vast network of virus-host interactions.
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Zhong Z, McCafferty S, Opsomer L, Wang H, Huysmans H, De Temmerman J, Lienenklaus S, Portela Catani JP, Combes F, Sanders NN. Corticosteroids and cellulose purification improve, respectively, the in vivo translation and vaccination efficacy of sa-mRNAs. Mol Ther 2021; 29:1370-1381. [PMID: 33484964 DOI: 10.1016/j.ymthe.2021.01.023] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 12/18/2020] [Accepted: 01/12/2021] [Indexed: 12/22/2022] Open
Abstract
Synthetic mRNAs are an appealing platform with multiple biomedical applications ranging from protein replacement therapy to vaccination. In comparison with conventional mRNA, synthetic self-amplifying mRNAs (sa-mRNAs) are gaining interest because of their higher and longer-lasting expression. However, sa-mRNAs also elicit an innate immune response, which may complicate their clinical application. Approaches to reduce the innate immunity of sa-mRNAs have not been studied in detail. Here we investigated, in vivo, the effect of several innate immune inhibitors and a novel cellulose-based mRNA purification approach on the type I interferon (IFN) response and the translation and vaccination efficacy of our formerly developed sa-mRNA vaccine against Zika virus. Among the investigated inhibitors, we found that corticosteroids and especially topical application of clobetasol at the sa-mRNA injection site was the most efficient in suppressing the type I IFN response and increasing the translation of sa-mRNA. However, clobetasol prevented formation of antibodies against sa-mRNA-encoded antigens and should therefore be avoided in a vaccination context. Residual dsRNA by-products of the in vitro transcription reaction are known inducers of immediate type I IFN responses. We additionally demonstrate a drastic reduction of these dsRNA by-products upon cellulose-based purification, reducing the innate immune response and improving sa-mRNA vaccination efficacy.
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Affiliation(s)
- Zifu Zhong
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium
| | - Séan McCafferty
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium; Cancer Research Institute (CRIG), Ghent University, 9000 Ghent, Belgium
| | - Lisa Opsomer
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium
| | - Haixiu Wang
- Laboratory of Immunology, Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
| | - Hanne Huysmans
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium
| | - Joyca De Temmerman
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium; Department of Pathology, Bacteriology and Poultry Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium
| | - Stefan Lienenklaus
- Institute for Laboratory Animal Science, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
| | - João Paulo Portela Catani
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium
| | - Francis Combes
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium; Cancer Research Institute (CRIG), Ghent University, 9000 Ghent, Belgium
| | - Niek N Sanders
- Laboratory of Gene Therapy, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, 9820 Merelbeke, Belgium; Cancer Research Institute (CRIG), Ghent University, 9000 Ghent, Belgium.
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19
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Jones R, Bragagnolo G, Arranz R, Reguera J. Capping pores of alphavirus nsP1 gate membranous viral replication factories. Nature 2020; 589:615-619. [PMID: 33328629 PMCID: PMC7739802 DOI: 10.1038/s41586-020-3036-8] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Accepted: 10/21/2020] [Indexed: 12/23/2022]
Abstract
Positive-sense single-stranded RNA viruses, such as coronaviruses, flaviviruses and alphaviruses, carry out transcription and replication inside virus-induced membranous organelles within host cells1–7. The remodelling of the host-cell membranes for the formation of these organelles is coupled to the membrane association of viral replication complexes and to RNA synthesis. These viral niches allow for the concentration of metabolites and proteins for the synthesis of viral RNA, and prevent the detection of this RNA by the cellular innate immune system8. Here we present the cryo-electron microscopy structure of non-structural protein 1 (nsP1) of the alphavirus chikungunya virus, which is responsible for RNA capping and membrane binding of the viral replication machinery. The structure shows the enzyme in its active form, assembled in a monotopic membrane-associated dodecameric ring. The structure reveals the structural basis of the coupling between membrane binding, oligomerization and allosteric activation of the capping enzyme. The stoichiometry—with 12 active sites in a single complex—redefines viral replication complexes as RNA synthesis reactors. The ring shape of the complex implies it has a role in controlling access to the viral organelle and ensuring the exit of properly capped viral RNA. Our results provide high-resolution information about the membrane association of the replication machinery of positive-sense single-stranded RNA viruses, and open up avenues for the further characterization of viral replication on cell membranes and the generation of antiviral agents. Cryo-electron microscopy structures of non-structural protein 1 (nsP1) of chikungunya virus reveal the mechanisms that underpin the association of viral replication machinery with virus-induced membranous organelles within host cells.
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Affiliation(s)
- Rhian Jones
- Aix-Marseille Université, CNRS, AFMB UMR 7257, Marseille, France
| | | | - Rocío Arranz
- National Center of Biotechnology, CSIC, Madrid, Spain
| | - Juan Reguera
- Aix-Marseille Université, CNRS, AFMB UMR 7257, Marseille, France. .,INSERM, AFMB UMR7257, Marseille, France.
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20
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Cerikan B, Goellner S, Neufeldt CJ, Haselmann U, Mulder K, Chatel-Chaix L, Cortese M, Bartenschlager R. A Non-Replicative Role of the 3' Terminal Sequence of the Dengue Virus Genome in Membranous Replication Organelle Formation. Cell Rep 2020; 32:107859. [PMID: 32640225 PMCID: PMC7351112 DOI: 10.1016/j.celrep.2020.107859] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 04/11/2020] [Accepted: 06/12/2020] [Indexed: 12/14/2022] Open
Abstract
Dengue virus (DENV) and Zika virus (ZIKV), members of the Flavivirus genus, rearrange endoplasmic reticulum membranes to induce invaginations known as vesicle packets (VPs), which are the assumed sites for viral RNA replication. Mechanistic information on VP biogenesis has so far been difficult to attain due to the necessity of studying their formation under conditions of viral replication, where perturbations reducing replication will inevitably impact VP formation. Here, we report a replication-independent expression system, designated pIRO (plasmid-induced replication organelle formation) that induces bona fide DENV and ZIKV VPs that are morphologically indistinguishable from those in infected cells. Using this system, we demonstrate that sequences in the 3' terminal RNA region of the DENV, but not the ZIKV genome, contribute to VP formation in a non-replicative manner. These results validate the pIRO system that opens avenues for mechanistically dissecting virus replication from membrane reorganization.
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Affiliation(s)
- Berati Cerikan
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Sarah Goellner
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Christopher John Neufeldt
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Uta Haselmann
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Klaas Mulder
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Laurent Chatel-Chaix
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Mirko Cortese
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany
| | - Ralf Bartenschlager
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany; German Center for Infection Research (DZIF), Heidelberg Partner Site, University, 69120 Heidelberg, Germany.
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21
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Gottipati K, Woodson M, Choi KH. Membrane binding and rearrangement by chikungunya virus capping enzyme nsP1. Virology 2020; 544:31-41. [PMID: 32174512 PMCID: PMC7103501 DOI: 10.1016/j.virol.2020.02.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Revised: 02/17/2020] [Accepted: 02/23/2020] [Indexed: 01/20/2023]
Abstract
Alphavirus genome replication is carried out by the viral replication complex inside modified membrane structures called spherules. The viral nonstructural protein 1 (nsP1) is the only membrane-associated protein that anchors the replication complex to the cellular membranes. Although an internal amphipathic helix of nsP1 is critical for membrane association, the mechanism of nsP1 interaction with membranes and subsequent membrane reorganization is not well understood. We studied the membrane interaction of chikungunya virus (CHIKV) nsP1 and show that both the CHIKV nsP1 protein and the amphipathic peptide specifically bind to negatively charged phospholipid vesicles. Using cryo-electron microscopy, we further show that nsP1 forms a contiguous coat on lipid vesicles and induces structural reorganization, while the amphipathic peptide alone failed to deform the membrane bilayer. This suggests that although amphipathic helix of nsP1 is required for initial membrane binding, the remaining cytoplasmic domain of nsP1 is involved in the subsequent membrane reorganization.
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Affiliation(s)
- Keerthi Gottipati
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX, USA.
| | - Michael Woodson
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX, USA
| | - Kyung H Choi
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX, USA.
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Sensitivity of Alphaviruses to G3BP Deletion Correlates with Efficiency of Replicase Polyprotein Processing. J Virol 2020; 94:JVI.01681-19. [PMID: 31941782 DOI: 10.1128/jvi.01681-19] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 01/02/2020] [Indexed: 11/20/2022] Open
Abstract
We present a comprehensive overview of the dependency of several Old World alphaviruses for the host protein G3BP. Based on their replication ability in G3BP-deleted cells, Old World alphaviruses can be categorized into two groups, being either resistant or sensitive to G3BP deletion. We observed that all sensitive viruses have an Arg residue at the P4 position of the cleavage site between the nonstructural protein P1 (nsP1) and nsP2 regions of the replicase precursor polyprotein (1/2 site), while a different residue is found at this site in viruses resistant to G3BP deletion. Swapping this residue between resistant and sensitive viruses also switches the G3BP deletion sensitivity. In the absence of G3BP, chikungunya virus (CHIKV) replication is at the limit of detection. The P4 Arg-to-His substitution partially rescues this defect. The P4 residue of the 1/2 site is known to play a regulatory role during processing at this site, and we found that if processing is blocked, the influence of the P4 residue on the sensitivity to G3BP deletion is abolished. Immunofluorescence experiments with CHIKV replicase with manipulated processing indicate that the synthesis of double-stranded RNA is defective in the absence of G3BP and suggest a role of G3BP during negative-strand RNA synthesis. This study provides a functional link between the host protein G3BP and the P4 residue of the 1/2 site for viral RNA replication of Old World alphaviruses. While this suggests a link between G3BP proteins and viral replicase polyprotein processing, we propose that G3BP proteins do not have a regulatory role during polyprotein processing.IMPORTANCE Old World alphaviruses comprise several medically relevant viruses, including chikungunya virus and Ross River virus. Recurrent outbreaks and the lack of antivirals and vaccines demand ongoing research to fight the emergence of these infectious diseases. In this context, a thorough investigation of virus-host interactions is critical. Here, we highlight the importance of the host protein G3BP for several Old World alphaviruses. Our data strongly suggest that G3BP plays a crucial role for the activity of the viral replicase and, thus, the amplification of the viral RNA genome. To our knowledge, the present work is the first to provide a functional link between the regulation of viral polyprotein processing and RNA replication and a host factor for alphaviruses. Moreover, the results of this study raise several questions about the fundamental regulatory mechanisms that dictate the activity of the viral replicase, thereby paving the way for future studies.
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Design and Use of Chikungunya Virus Replication Templates Utilizing Mammalian and Mosquito RNA Polymerase I-Mediated Transcription. J Virol 2019; 93:JVI.00794-19. [PMID: 31217251 DOI: 10.1128/jvi.00794-19] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 06/18/2019] [Indexed: 01/20/2023] Open
Abstract
Chikungunya virus (CHIKV) is a mosquito-borne alphavirus. It has a positive-sense RNA genome that also serves as the mRNA for four nonstructural proteins (nsPs) representing subunits of the viral replicase. Coupling of nsP and RNA synthesis complicates analysis of viral RNA replication. We developed trans-replication systems, where production of replication-competent RNA and expression of viral replicase are uncoupled. Mammalian and mosquito RNA polymerase I promoters were used to produce noncapped RNA templates, which are poorly translated relative to CHIKV replicase-generated capped RNAs. It was found that, in human cells, constructs driven by RNA polymerase I promoters of human and Chinese hamster origin performed equally well. In contrast, RNA polymerase I promoters from Aedes mosquitoes exhibited strong species specificity. In both mammalian and mosquito cells, novel trans-replicase assays had exceptional sensitivity, with up to 105-fold higher reporter expression in the presence of replicase relative to background. Using this highly sensitive assay to analyze CHIKV nsP1 functionality, several mutations that severely reduced, but did not completely block, CHIKV replicase activity were identified: (i) nsP1 tagged at its N terminus with enhanced green fluorescent protein; (ii) mutations D63A and Y248A, blocking the RNA capping; and (iii) mutation R252E, affecting nsP1 membrane anchoring. In contrast, a mutation in the nsP1 palmitoylation site completely inactivated CHIKV replicase in both human and mosquito cells and was lethal for the virus. Our data confirm that this novel system provides a valuable tool to study CHIKV replicase, RNA replication, and virus-host interactions.IMPORTANCE Chikungunya virus (CHIKV) is a medically important pathogen responsible for recent large-scale epidemics. The development of efficient therapies against CHIKV has been hampered by gaps in our understanding of how nonstructural proteins (nsPs) function to form the viral replicase and replicate virus RNA. Here we describe an extremely sensitive assay to analyze the effects of mutations on the virus RNA synthesis machinery in cells of both mammalian (host) and mosquito (vector) origin. Using this system, several lethal mutations in CHIKV nsP1 were shown to reduce but not completely block the ability of its replicase to synthesize viral RNAs. However, in contrast to related alphaviruses, CHIKV replicase was completely inactivated by mutations preventing palmitoylation of nsP1. These data can be used to develop novel, virus-specific antiviral treatments.
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Tsika AC, Melekis E, Tsatsouli SA, Papageorgiou N, Maté MJ, Canard B, Coutard B, Bentrop D, Spyroulias GA. Deciphering the Nucleotide and RNA Binding Selectivity of the Mayaro Virus Macro Domain. J Mol Biol 2019; 431:2283-2297. [PMID: 30998933 PMCID: PMC7094482 DOI: 10.1016/j.jmb.2019.04.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 03/01/2019] [Accepted: 04/08/2019] [Indexed: 12/25/2022]
Abstract
Mayaro virus (MAYV) is a member of Togaviridae family, which also includes Chikungunya virus as a notorious member. MAYV recently emerged in urban areas of the Americas, and this emergence emphasized the current paucity of knowledge about its replication cycle. The macro domain (MD) of MAYV belongs to the N-terminal region of its non-structural protein 3, part of the replication complex. Here, we report the first structural and dynamical characterization of a previously unexplored Alphavirus MD investigated through high-resolution NMR spectroscopy, along with data on its ligand selectivity and binding properties. The structural analysis of MAYV MD reveals a typical "macro" (ββαββαβαβα) fold for this polypeptide, while NMR-driven interaction studies provide in-depth insights into MAYV MD-ligand adducts. NMR data in concert with thermodynamics and biochemical studies provide convincing experimental evidence for preferential binding of adenosine diphosphate ribose (ADP-r) and adenine-rich RNAs to MAYV MD, thus shedding light on the structure-function relationship of a previously unexplored viral MD. The emerging differences with any other related MD are expected to enlighten distinct functions.
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Affiliation(s)
| | | | | | | | - Maria J Maté
- AFMB, UMR7257 CNRS/Aix Marseille Université, Marseille, CEDEX 9, France
| | - Bruno Canard
- AFMB, UMR7257 CNRS/Aix Marseille Université, Marseille, CEDEX 9, France
| | - Bruno Coutard
- UVE: Aix-Marseille Univ-IRD 190-Inserm 27-IHU Méditerranée Infection, Marseille, France.
| | - Detlef Bentrop
- Institute of Physiology II, Faculty of Medicine, University of Freiburg, D-79104 Freiburg, Germany
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25
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Carissimo G, Ng LFP. Understanding Molecular Pathogenesis with Chikungunya Virus Research Tools. Curr Top Microbiol Immunol 2019; 435:33-53. [PMID: 30888547 DOI: 10.1007/82_2019_158] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Since its re-emergence in 2006, Chikungunya has been a major health concern in endemic areas. Transmitted by Aedes mosquitoes to mammalian hosts, Chikungunya leads to persistent debilitating symptoms in a high proportion of symptomatic human cases. In this review, we present several tools on the mosquito vector side as well as on the mammalian side that have been used to advance research on Chikungunya transmission and immunopathogenesis. These tools lead to key understandings of viral replication in both hosts, and innate and adaptive responses mediating virus clearance and pathology in mammals. This comprehension of viral mechanisms has allowed the development of promising treatment avenues in animal models that will need to be further explored. However, research efforts need to continue in order to develop better and unbiased tools to assess antiviral and treatment strategies as well as further understand immune mechanisms at play in human pathologies.
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Affiliation(s)
- Guillaume Carissimo
- Singapore Immunology Network (SIgN), Agency for Science, Technology and Research (A*STAR), Biopolis, Singapore, Singapore
| | - Lisa F P Ng
- Singapore Immunology Network (SIgN), Agency for Science, Technology and Research (A*STAR), Biopolis, Singapore, Singapore. .,Institute of Infection and Global Health, University of Liverpool, Liverpool, UK. .,Laboratory of Microbial Immunity, Singapore Immunology Network, 8A Biomedical Grove, #04-06, Immunos, Biopolis, 138648, Singapore.
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26
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Cowpea chlorotic mottle bromovirus replication proteins support template-selective RNA replication in Saccharomyces cerevisiae. PLoS One 2018; 13:e0208743. [PMID: 30586378 PMCID: PMC6306254 DOI: 10.1371/journal.pone.0208743] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 11/22/2018] [Indexed: 11/19/2022] Open
Abstract
Positive-strand RNA viruses generally assemble RNA replication complexes on rearranged host membranes. Alphaviruses, other members of the alpha-like virus superfamily, and many other positive-strand RNA viruses invaginate host membrane into vesicular RNA replication compartments, known as spherules, whose interior is connected to the cytoplasm. Brome mosaic virus (BMV) and its close relative, cowpea chlorotic mottle virus (CCMV), form spherules along the endoplasmic reticulum. BMV spherule formation and RNA replication can be fully reconstituted in S. cerevisiae, enabling many studies identifying host factors and viral interactions essential for these processes. To better define and understand the conserved, core pathways of bromovirus RNA replication, we tested the ability of CCMV to similarly support spherule formation and RNA replication in yeast. Paralleling BMV, we found that CCMV RNA replication protein 1a was the only viral factor necessary to induce spherule membrane rearrangements and to recruit the viral 2a polymerase (2apol) to the endoplasmic reticulum. CCMV 1a and 2apol also replicated CCMV and BMV genomic RNA2, demonstrating core functionality of CCMV 1a and 2apol in yeast. However, while BMV and CCMV 1a/2apol strongly replicate each others’ genomic RNA3 in plants, neither supported detectable CCMV RNA3 replication in yeast. Moreover, in contrast to plant cells, in yeast CCMV 1a/2apol supported only limited replication of BMV RNA3 (<5% of that by BMV 1a/2apol). In keeping with this, we found that in yeast CCMV 1a was significantly impaired in recruiting BMV or CCMV RNA3 to the replication complex. Overall, we show that many 1a and 2apol functions essential for replication complex assembly, and their ability to be reconstituted in yeast, are conserved between BMV and CCMV. However, restrictions of CCMV RNA replication in yeast reveal previously unknown 1a-linked, RNA-selective host contributions to the essential early process of recruiting viral RNA templates to the replication complex.
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27
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The RNA Capping Enzyme Domain in Protein A is Essential for Flock House Virus Replication. Viruses 2018; 10:v10090483. [PMID: 30205593 PMCID: PMC6165433 DOI: 10.3390/v10090483] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 09/05/2018] [Accepted: 09/05/2018] [Indexed: 01/18/2023] Open
Abstract
The nodavirus flock house virus (FHV) and the alphavirus Semliki Forest virus (SFV) show evolutionarily intriguing similarities in their replication complexes and RNA capping enzymes. In this study, we first established an efficient FHV trans-replication system in mammalian cells, which disjoins protein expression from viral RNA synthesis. Following transfection, FHV replicase protein A was associated with mitochondria, whose outer surface displayed pouch-like invaginations with a ‘neck’ structure opening towards the cytoplasm. In mitochondrial pellets from transfected cells, high-level synthesis of both genomic and subgenomic RNA was detected in vitro and the newly synthesized RNA was of positive polarity. Secondly, we initiated the study of the putative RNA capping enzyme domain in protein A by mutating the conserved amino acids H93, R100, D141, and W215. RNA replication was abolished for all mutants inside cells and in vitro except for W215A, which showed reduced replication. Transfection of capped RNA template did not rescue the replication activity of the mutants. Comparing the efficiency of SFV and FHV trans-replication systems, the FHV system appeared to produce more RNA. Using fluorescent marker proteins, we demonstrated that both systems could replicate in the same cell. This work may facilitate the comparative analysis of FHV and SFV replication.
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28
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Doyle N, Neuman BW, Simpson J, Hawes PC, Mantell J, Verkade P, Alrashedi H, Maier HJ. Infectious Bronchitis Virus Nonstructural Protein 4 Alone Induces Membrane Pairing. Viruses 2018; 10:v10090477. [PMID: 30200673 PMCID: PMC6163833 DOI: 10.3390/v10090477] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Revised: 09/03/2018] [Accepted: 09/05/2018] [Indexed: 01/20/2023] Open
Abstract
Positive-strand RNA viruses, such as coronaviruses, induce cellular membrane rearrangements during replication to form replication organelles allowing for efficient viral RNA synthesis. Infectious bronchitis virus (IBV), a pathogenic avian Gammacoronavirus of significant importance to the global poultry industry, has been shown to induce the formation of double membrane vesicles (DMVs), zippered endoplasmic reticulum (zER) and tethered vesicles, known as spherules. These membrane rearrangements are virally induced; however, it remains unclear which viral proteins are responsible. In this study, membrane rearrangements induced when expressing viral non-structural proteins (nsps) from two different strains of IBV were compared. Three non-structural transmembrane proteins, nsp3, nsp4, and nsp6, were expressed in cells singularly or in combination and the effects on cellular membranes investigated using electron microscopy and electron tomography. In contrast to previously studied coronaviruses, IBV nsp4 alone is necessary and sufficient to induce membrane pairing; however, expression of the transmembrane proteins together was not sufficient to fully recapitulate DMVs. This indicates that although nsp4 is able to singularly induce membrane pairing, further viral or host factors are required in order to fully assemble IBV replicative structures. This study highlights further differences in the mechanism of membrane rearrangements between members of the coronavirus family.
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Affiliation(s)
- Nicole Doyle
- The Pirbright Institute, Pirbright, Surrey GU24 0NF, UK.
| | - Benjamin W Neuman
- School of Biological Sciences, University of Reading, Reading RG6 6AJ, UK.
| | | | | | - Judith Mantell
- School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
| | - Paul Verkade
- School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
| | - Hasan Alrashedi
- School of Biological Sciences, University of Reading, Reading RG6 6AJ, UK.
| | - Helena J Maier
- The Pirbright Institute, Pirbright, Surrey GU24 0NF, UK.
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29
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Lulla V, Karo-Astover L, Rausalu K, Saul S, Merits A, Lulla A. Timeliness of Proteolytic Events Is Prerequisite for Efficient Functioning of the Alphaviral Replicase. J Virol 2018; 92:e00151-18. [PMID: 29695431 PMCID: PMC6026757 DOI: 10.1128/jvi.00151-18] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 04/16/2018] [Indexed: 11/20/2022] Open
Abstract
Polyprotein processing has an important regulatory role in the life cycle of positive-strand RNA viruses. In the case of alphaviruses, sequential cleavage of the nonstructural polyprotein (ns-polyprotein) at three sites eventually yields four mature nonstructural proteins (nsPs) that continue working in complex to replicate viral genomic RNA and transcribe subgenomic RNA. Recognition of cleavage sites by viral nsP2 protease is guided by short sequences upstream of the scissile bond and, more importantly, by the spatial organization of the replication complex. In this study, we analyzed the consequences of the artificially accelerated processing of the Semliki Forest virus ns-polyprotein. It was found that in mammalian cells, not only the order but also the correct timing of the cleavage events is essential for the success of viral replication. Analysis of the effects of compensatory mutations in rescued viruses as well as in vitro translation and trans-replicase assays corroborated our findings and revealed the importance of the V515 residue in nsP2 for recognizing the P4 position in the nsP1/nsP2 cleavage site. We also extended our conclusions to Sindbis virus by analyzing the properties of the hyperprocessive variant carrying the N614D mutation in nsP2. We conclude that the sequence of the nsP1/nsP2 site in alphaviruses is under selective pressure to avoid the presence of sequences that are recognized too efficiently and would otherwise lead to premature cleavage at this site before completion of essential tasks of RNA synthesis or virus-induced replication complex formation. Even subtle changes in the ns-polyprotein processing pattern appear to lead to virus attenuation.IMPORTANCE The polyprotein expression strategy is a cornerstone of alphavirus replication. Three sites within the ns-polyprotein are recognized by the viral nsP2 protease and cleaved in a defined order. Specific substrate targeting is achieved by the recognition of the short sequence upstream of the scissile bond and a correct macromolecular assembly of ns-polyprotein. Here, we highlighted the importance of the timeliness of proteolytic events, as an additional layer of regulation of efficient virus replication. We conclude that, somewhat counterintuitively, the cleavage site sequences at the nsP1/nsP2 and nsP2/nsP3 junctions are evolutionarily selected to be recognized by protease inefficiently, to avoid premature cleavages that would be detrimental for the assembly and functionality of the replication complex. Understanding the causes and consequences of viral polyprotein processing events is important for predicting the properties of mutant viruses and should be helpful for the development of better vaccine candidates and understanding potential mechanisms of resistance to protease inhibitors.
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Affiliation(s)
- Valeria Lulla
- Institute of Technology, University of Tartu, Tartu, Estonia
| | | | - Kai Rausalu
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Sirle Saul
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Andres Merits
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Aleksei Lulla
- Institute of Technology, University of Tartu, Tartu, Estonia
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30
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Bartholomeeusen K, Utt A, Coppens S, Rausalu K, Vereecken K, Ariën KK, Merits A. A Chikungunya Virus trans-Replicase System Reveals the Importance of Delayed Nonstructural Polyprotein Processing for Efficient Replication Complex Formation in Mosquito Cells. J Virol 2018; 92:e00152-18. [PMID: 29695432 PMCID: PMC6026725 DOI: 10.1128/jvi.00152-18] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 04/23/2018] [Indexed: 12/16/2022] Open
Abstract
Chikungunya virus (CHIKV) is a medically important alphavirus that is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. The viral replicase complex consists of four nonstructural proteins (nsPs) expressed as a polyprotein precursor and encompasses all enzymatic activities required for viral RNA replication. nsPs interact with host components of which most are still poorly understood, especially in mosquitos. A CHIKV trans-replicase system that allows the uncoupling of RNA replication and nsP expression was adapted to mosquito cells and subsequently used for analysis of universal and host-specific effects of 17 different nonstructural polyprotein (ns-polyprotein) mutations. It was found that mutations blocking nsP enzymatic activities as well as insertions of enhanced green fluorescent protein (EGFP) into different nsPs had similar effects on trans-replicase activity regardless of the host (i.e., mammalian or mosquito). Mutations that slow down or accelerate ns-polyprotein processing generally had no effect or reduced trans-replicase activity in mammalian cells, while in mosquito cells most of them increased trans-replicase activity prominently. Increased RNA replication in mosquito cells was counteracted by an antiviral RNA interference (RNAi) response. Substitution of the W258 residue in the membrane binding peptide of nsP1 resulted in a temperature-sensitive defect, in the context of both the trans-replicase and infectious CHIKV. The defect was compensated for by secondary mutations selected during passaging of mutant CHIKV. These findings demonstrate the value of alphavirus trans-replicase systems for studies of viral RNA replication and virus-host interactions.IMPORTANCE Chikungunya virus is an important mosquito-transmitted human pathogen. This virus actively replicates in mosquitoes, but the underlying molecular mechanisms and interactions of viral and host components are poorly understood. This is partly due to the lack of reliable systems for functional analysis of viral nonstructural polyproteins (ns-polyproteins) and nonstructural proteins (nsPs) in mosquito cells. Adaption of a CHIKV trans-replicase system allowed study of the effects of mutations in the ns-polyprotein on RNA replication in cells derived from mammalian and mosquito hosts. We found that a slowdown of ns-polyprotein processing facilitates replication complex formation and/or functioning in mosquito cells and that this process is antagonized by the natural RNAi defense system present in mosquito cells. The mosquito-adapted CHIKV trans-replicase system represents a valuable tool to study alphavirus-mosquito interactions at the molecular level and to develop advanced antiviral strategies.
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Affiliation(s)
- Koen Bartholomeeusen
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Age Utt
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Sandra Coppens
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Kai Rausalu
- Institute of Technology, University of Tartu, Tartu, Estonia
| | - Katleen Vereecken
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Kevin K Ariën
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
- Department of Biomedical Sciences, University of Antwerp, Wilrijk, Belgium
| | - Andres Merits
- Institute of Technology, University of Tartu, Tartu, Estonia
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31
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The Regulation of Translation in Alphavirus-Infected Cells. Viruses 2018; 10:v10020070. [PMID: 29419763 PMCID: PMC5850377 DOI: 10.3390/v10020070] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 02/02/2018] [Accepted: 02/06/2018] [Indexed: 12/12/2022] Open
Abstract
Sindbis virus (SINV) contains an RNA genome of positive polarity with two open reading frames (ORFs). The first ORF is translated from the genomic RNA (gRNA), rendering the viral non-structural proteins, whereas the second ORF is translated from a subgenomic mRNA (sgRNA), which directs the synthesis of viral structural proteins. SINV infection strongly inhibits host cell translation through a variety of different mechanisms, including the phosphorylation of the eukaryotic initiation factor eIF2α and the redistribution of cellular proteins from the nucleus to the cytoplasm. A number of motifs have been identified in SINV sgRNA, including a hairpin downstream of the AUG initiation codon, which is involved in the translatability of the viral sgRNA when eIF2 is inactivated. Moreover, a 3′-UTR motif containing three stem-loop structures is involved in the enhancement of translation in insect cells, but not in mammalian cells. Accordingly, SINV sgRNA has evolved several structures to efficiently compete for the cellular translational machinery. Mechanistically, sgRNA translation involves scanning of the 5′-UTR following a non-canonical mode and without the requirement for several initiation factors. Indeed, sgRNA-directed polypeptide synthesis occurs even after eIF4G cleavage or inactivation of eIF4A by selective inhibitors. Remarkably, eIF2α phosphorylation does not hamper sgRNA translation during the late phase of SINV infection. SINV sgRNA thus constitutes a unique model of a capped viral mRNA that is efficiently translated in the absence of several canonical initiation factors. The present review will mainly focus in the non-canonical mechanism of translation of SINV sgRNA.
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32
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Zhang XF, Zhang S, Guo Q, Sun R, Wei T, Qu F. A New Mechanistic Model for Viral Cross Protection and Superinfection Exclusion. FRONTIERS IN PLANT SCIENCE 2018; 9:40. [PMID: 29422912 PMCID: PMC5788904 DOI: 10.3389/fpls.2018.00040] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Accepted: 01/09/2018] [Indexed: 05/05/2023]
Abstract
Plants pre-infected with a mild variant of a virus frequently become protected against more severe variants of the same virus through the cross protection phenomenon first discovered in 1929. Despite its widespread use in managing important plant virus diseases, the mechanism of cross protection remains poorly understood. Recent investigations in our labs, by analyzing the whole-plant dynamics of a turnip crinkle virus (TCV) population, coupled with cell biological interrogation of individual TCV variants, revealed possible novel mechanisms for cross protection and the closely related process of superinfection exclusion (SIE). Our new mechanistic model postulates that, for RNA viruses like TCV, SIE manifests a viral function that denies progeny viruses the chance of re-replicating their genomes in the cells of their "parents," and it collaterally targets highly homologous superinfecting viruses that are indistinguishable from progeny viruses. We further propose that SIE may be evolutionarily selected to maintain an optimal error frequency in progeny genomes. Although primarily based on observations made with TCV, this new model could be broadly applicable to other viruses as it provides a molecular basis for maintaining virus genome fidelity in the face of the error-prone nature of virus replication process.
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Affiliation(s)
- Xiao-Feng Zhang
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Key Laboratory of Plant Virology, Institute of Plant Virology, Fujian Agriculture and Forestry University, Fuzhou, China
- *Correspondence: Feng Qu, Xiao-Feng Zhang,
| | - Shaoyan Zhang
- Department of Plant Pathology, Ohio Agricultural Research and Development Center, Ohio State University, Wooster, OH, United States
| | - Qin Guo
- Department of Plant Pathology, Ohio Agricultural Research and Development Center, Ohio State University, Wooster, OH, United States
| | - Rong Sun
- Department of Plant Pathology, Ohio Agricultural Research and Development Center, Ohio State University, Wooster, OH, United States
| | - Taiyun Wei
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Key Laboratory of Plant Virology, Institute of Plant Virology, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Feng Qu
- Department of Plant Pathology, Ohio Agricultural Research and Development Center, Ohio State University, Wooster, OH, United States
- *Correspondence: Feng Qu, Xiao-Feng Zhang,
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33
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Pietilä MK, Albulescu IC, Hemert MJV, Ahola T. Polyprotein Processing as a Determinant for in Vitro Activity of Semliki Forest Virus Replicase. Viruses 2017; 9:v9100292. [PMID: 28991178 PMCID: PMC5691643 DOI: 10.3390/v9100292] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Revised: 09/29/2017] [Accepted: 10/03/2017] [Indexed: 12/11/2022] Open
Abstract
Semliki Forest virus (SFV) is an arthropod-borne alphavirus that induces membrane invaginations (spherules) in host cells. These harbor the viral replication complexes (RC) that synthesize viral RNA. Alphaviruses have four replicase or nonstructural proteins (nsPs), nsP1-4, expressed as polyprotein P1234. An early RC, which synthesizes minus-strand RNA, is formed by the polyprotein P123 and the polymerase nsP4. Further proteolytic cleavage results in a late RC consisting of nsP1-4 and synthesizing plus strands. Here, we show that only the late RCs are highly active in RNA synthesis in vitro. Furthermore, we demonstrate that active RCs can be isolated from both virus-infected cells and cells transfected with the wild-type replicase in combination with a plasmid expressing a template RNA. When an uncleavable polyprotein P123 and polymerase nsP4 were expressed together with a template, high levels of minus-strand RNA were produced in cells, but RCs isolated from these cells were hardly active in vitro. Furthermore, we observed that the uncleavable polyprotein P123 and polymerase nsP4, which have previously been shown to form spherules even in the absence of the template, did not replicate an exogenous template. Consequently, we hypothesize that the replicase proteins were sequestered in spherules and were no longer able to recruit a template.
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Affiliation(s)
- Maija K Pietilä
- Department of Food and Environmental Sciences, University of Helsinki, Viikinkaari 9 PO Box 56, 00014 Helsinki, Finland.
| | - Irina C Albulescu
- Department of Medical Microbiology, Leiden University Medical Center PO Box 9600, 2300 RC, Leiden, The Netherlands.
| | - Martijn J van Hemert
- Department of Medical Microbiology, Leiden University Medical Center PO Box 9600, 2300 RC, Leiden, The Netherlands.
| | - Tero Ahola
- Department of Food and Environmental Sciences, University of Helsinki, Viikinkaari 9 PO Box 56, 00014 Helsinki, Finland.
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