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Quinteros JA, Browning GF, Mardani K, Noormohammadi AH, Stevenson MA, Coppo MJC, Loncoman CA, Ficorilli N, Diaz-Méndez A. Adding yeast extract to culture medium enhances replication of the avian coronavirus infectious bronchitis virus in chicken embryo kidney cells. J Virol Methods 2024; 329:114989. [PMID: 38917942 DOI: 10.1016/j.jviromet.2024.114989] [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: 02/15/2024] [Revised: 06/04/2024] [Accepted: 06/16/2024] [Indexed: 06/27/2024]
Abstract
Infectious bronchitis virus (IBV), an avian coronavirus, can be isolated and cultured in tracheal organ cultures (TOCs), embryonated eggs and cell cultures, the first two of which are commonly used for viral isolation. Previous studies have suggested that foetal bovine serum (FBS) can inhibit coronavirus replication in cell cultures. In this study, the replication of IBV in chicken embryo kidney (CEK) cell cultures and the Leghorn hepatocellular carcinoma (LMH) cell line was assessed using two different cell culture media containing FBS or yeast extract (YE) and two different IBV strains. The highest concentrations of viral genomes were observed when the cell culture medium (CEK) contained YE. Similar results were observed in LMH cells. Examination of the infectivity by titration demonstrated that the cell lysate from CEK cell cultures in a medium including YE contained a higher median embryo infectious dose than that from CEK cell cultures in a medium containing FBS. These results indicate that improved replication of IBV in cell cultures can be achieved by replacing FBS with YE in the cell culture medium.
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Affiliation(s)
- José A Quinteros
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia.
| | - Glenn F Browning
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Karim Mardani
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Amir H Noormohammadi
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Werribee, VIC 3030, Australia
| | - Mark A Stevenson
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Mauricio J C Coppo
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Carlos A Loncoman
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Nino Ficorilli
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Andrés Diaz-Méndez
- Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, Faculty of Science, The University of Melbourne, Parkville, VIC 3010, Australia
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2
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Wang X, Chen Y, Qi C, Li F, Zhang Y, Zhou J, Wu H, Zhang T, Qi A, Ouyang H, Xie Z, Pang D. Mechanism, structural and functional insights into nidovirus-induced double-membrane vesicles. Front Immunol 2024; 15:1340332. [PMID: 38919631 PMCID: PMC11196420 DOI: 10.3389/fimmu.2024.1340332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Accepted: 05/22/2024] [Indexed: 06/27/2024] Open
Abstract
During infection, positive-stranded RNA causes a rearrangement of the host cell membrane, resulting in specialized membrane structure formation aiding viral genome replication. Double-membrane vesicles (DMVs), typical structures produced by virus-induced membrane rearrangements, are platforms for viral replication. Nidoviruses, one of the most complex positive-strand RNA viruses, have the ability to infect not only mammals and a few birds but also invertebrates. Nidoviruses possess a distinctive replication mechanism, wherein their nonstructural proteins (nsps) play a crucial role in DMV biogenesis. With the participation of host factors related to autophagy and lipid synthesis pathways, several viral nsps hijack the membrane rearrangement process of host endoplasmic reticulum (ER), Golgi apparatus, and other organelles to induce DMV formation. An understanding of the mechanisms of DMV formation and its structure and function in the infectious cycle of nidovirus may be essential for the development of new and effective antiviral strategies in the future.
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Affiliation(s)
- Xi Wang
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Yiwu Chen
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Chunyun Qi
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Feng Li
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Yuanzhu Zhang
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Jian Zhou
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Heyong Wu
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Tianyi Zhang
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Aosi Qi
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
| | - Hongsheng Ouyang
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
- Chongqing Research Institute, Jilin University, Chongqing, China
- Center for Animal Science and Technology Research, Chongqing Jitang Biotechnology Research Institute Co., Ltd, Chongqing, China
| | - Zicong Xie
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
- Chongqing Research Institute, Jilin University, Chongqing, China
| | - Daxin Pang
- Key Laboratory of Zoonosis Research, Ministry of Education, College of Animal Sciences, Jilin University, Changchun, Jilin, China
- Chongqing Research Institute, Jilin University, Chongqing, China
- Center for Animal Science and Technology Research, Chongqing Jitang Biotechnology Research Institute Co., Ltd, Chongqing, China
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3
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Choi A, Kots ED, Singleton DT, Weinstein H, Whittaker GR. Analysis of the molecular determinants for furin cleavage of the spike protein S1/S2 site in defined strains of the prototype coronavirus murine hepatitis virus (MHV). Virus Res 2024; 340:199283. [PMID: 38043726 PMCID: PMC10755501 DOI: 10.1016/j.virusres.2023.199283] [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: 08/08/2023] [Revised: 11/07/2023] [Accepted: 11/21/2023] [Indexed: 12/05/2023]
Abstract
We analyzed the spike protein S1/S2 cleavage of selected strains of a prototype coronavirus, mouse hepatitis virus (MHV) by the cellular protease furin, in order to understand the structural requirements underlying the sequence selectivity of the scissile segment. The probability of cleavage of selected MHV strains was first evaluated from furin cleavage scores predicted by the ProP computer software, and then cleavage was measured experimentally with a fluorogenic peptide cleavage assay consisting of S1/S2 peptide mimics and purified furin. We found that in vitro cleavability varied across MHV strains in line with predicted results-but with the notable exception of MHV-A59, which was not cleaved despite a high score predicted for its sequence. Using the known X-Ray structure of furin in complex with a substrate-like inhibitor as an initial structural reference, we carried out molecular dynamics (MD) simulations to learn the modes of binding of the peptides in the furin active site, and the suitability of the complex for initiation of the enzymatic cleavage. We identified the 3D structural requirements of the furin active site configuration that enable bound peptides to undergo cleavage, and the way in which the various strains tested experimentally are fulfilling these requirements. We find that despite some flexibility in the organization of the peptide bound to the active site of the enzyme, the presence of a histidine at P2 of MHV-A59 fails to properly orient the sidechain of His194 of the furin catalytic triad and therefore produces a distortion that renders the peptide/complex structural configuration in the active site incompatible with requirements for cleavage initiation. The Ser/Thr in P1 of MHV-2 and MHV-S has a similar effect of distorting the conformation of the furin active site residues produced by the elimination of the canonical salt-bridge formed by arginine in P1 position. This work informs a study of coronavirus infection and pathogenesis with respect to the function of the viral spike protein, and suggests an important process of viral adaptation and evolution within the spike S1/S2 structural loop.
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Affiliation(s)
- Annette Choi
- Departments of Microbiology & Immunology, Cornell University, Ithaca, NY, USA
| | - Ekaterina D Kots
- Department of Physiology & Biophysics, New York, NY, USA; Institute for Computational Biomedicine, Weill Cornell Medicine, New York, NY, USA
| | | | - Harel Weinstein
- Department of Physiology & Biophysics, New York, NY, USA; Institute for Computational Biomedicine, Weill Cornell Medicine, New York, NY, USA.
| | - Gary R Whittaker
- Departments of Microbiology & Immunology, Cornell University, Ithaca, NY, USA; Public & Ecosystem Health, Cornell University, Ithaca, NY, USA.
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4
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Dobrovolny HM. Mathematical Modeling of Virus-Mediated Syncytia Formation: Past Successes and Future Directions. Results Probl Cell Differ 2024; 71:345-370. [PMID: 37996686 DOI: 10.1007/978-3-031-37936-9_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2023]
Abstract
Many viruses have the ability to cause cells to fuse into large multi-nucleated cells, known as syncytia. While the existence of syncytia has long been known and its importance in helping spread viral infection within a host has been understood, few mathematical models have incorporated syncytia formation or examined its role in viral dynamics. This review examines mathematical models that have incorporated virus-mediated cell fusion and the insights they have provided on how syncytia can change the time course of an infection. While the modeling efforts are limited, they show promise in helping us understand the consequences of syncytia formation if future modeling efforts can be coupled with appropriate experimental efforts to help validate the models.
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Affiliation(s)
- Hana M Dobrovolny
- Department of Physics & Astronomy, Texas Christian University, Fort Worth, TX, USA.
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5
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Kim DM, Moon SH, Kim SC, Cho HS, Tark D. Development of Effective PEDV Vaccine Candidates Based on Viral Culture and Protease Activity. Vaccines (Basel) 2023; 11:vaccines11050923. [PMID: 37243027 DOI: 10.3390/vaccines11050923] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2023] [Revised: 04/27/2023] [Accepted: 04/28/2023] [Indexed: 05/28/2023] Open
Abstract
Porcine epidemic diarrhea (PED) is a highly contagious disease that has been reported annually in several Asian countries, causing significant economic losses to the swine livestock industry. Although vaccines against the porcine epidemic diarrhea virus (PEDV) are available, their efficacy remains questionable due to limitations such as viral genome mutation and insufficient intestinal mucosal immunity. Therefore, the development of a safe and effective vaccine is necessary. In this study, a virulent Korean strain of PEDV, CKT-7, was isolated from a piglet with severe diarrhea, and six different conditions were employed for serial passage of the strain in a cell culture system to generate effective live attenuated vaccine (LAV) candidates. The characteristics of these strains were analyzed in vitro and in vivo, and the CKT-7 N strain was identified as the most effective vaccine candidate, with a viral titer peak of 8.67 ± 0.29 log10TCID50/mL, and no mortality or diarrhea symptoms were observed in five-day-old piglets. These results indicate that LAV candidates can be generated through serial passage with different culture conditions and provide valuable insights into the development of a highly effective LAV against PEDV.
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Affiliation(s)
- Dae-Min Kim
- Laboratory for Infectious Disease Prevention, Korea Zoonosis Research Institute, Jeonbuk National University, Iksan 545431, Republic of Korea
| | - Sung-Hyun Moon
- College of Veterinary Medicine, Bio-Safety Research Institute, Jeonbuk National University, Iksan 54596, Republic of Korea
| | - Seung-Chai Kim
- College of Veterinary Medicine, Bio-Safety Research Institute, Jeonbuk National University, Iksan 54596, Republic of Korea
| | - Ho-Seong Cho
- College of Veterinary Medicine, Bio-Safety Research Institute, Jeonbuk National University, Iksan 54596, Republic of Korea
| | - Dongseob Tark
- Laboratory for Infectious Disease Prevention, Korea Zoonosis Research Institute, Jeonbuk National University, Iksan 545431, Republic of Korea
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6
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Kim J, Yoon J, Park JE. Furin cleavage is required for swine acute diarrhea syndrome coronavirus spike protein-mediated cell-cell fusion. Emerg Microbes Infect 2022; 11:2176-2183. [PMID: 35976165 PMCID: PMC9518401 DOI: 10.1080/22221751.2022.2114850] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Swine acute diarrhea syndrome coronavirus (SADS-CoV) was reported in China in 2017 and is a causative agent of porcine enteric disease. Recent studies indicate that cells from various hosts are susceptible to SADS-CoV, suggesting the zoonotic potential of this virus. However, little is known about the mechanisms through which this virus enters cells. In this study, we investigated the role of furin in SADS-CoV spike (S)-mediated cell-cell fusion and entry. We found that the SADS-CoV S protein induced the fusion of various cells. Cell-cell fusion was inhibited by the proprotein convertase inhibitor dec-RVKR-cmk, and between cells transfected with mutant S proteins resistant to furin cleavage. These findings revealed that furin-induced cleavage of the SADS-CoV S protein is required for cell-cell fusion. Using mutagenesis analysis, we demonstrated that furin cleaves the SADS-CoV S protein near the S1/S2 cleavage site, 446RYVR449 and 543AVRR546. We used pseudotyped viruses to determine whether furin-induced S cleavage is also required for viral entry. Pseudotyped viruses expressing S proteins with a mutated furin cleavage site could be transduced into target cells, indicating that furin-induced cleavage is not required for pseudotyped virus entry. Our data indicate that S cleavage is critical for SADS-CoV S-mediated cell-cell fusion and suggest that furin might be a host target for SADS-CoV antivirals.
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Affiliation(s)
- Jinman Kim
- Laboratory of Veterinary Public Health, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Jaewon Yoon
- Laboratory of Veterinary Public Health, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Jung-Eun Park
- Laboratory of Veterinary Public Health, College of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea.,Research Institute of Veterinary Medicine, Chungnam National University, Daejeon 34134, Republic of Korea
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7
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Sengupta S, Addya S, Biswas D, Banerjee P, Sarma JD. Matrix metalloproteinases and tissue inhibitors of metalloproteinases in murine β-coronavirus-induced neuroinflammation. Virology 2022; 566:122-135. [PMID: 34906793 PMCID: PMC8648396 DOI: 10.1016/j.virol.2021.11.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Revised: 11/16/2021] [Accepted: 11/26/2021] [Indexed: 01/17/2023]
Abstract
Mouse hepatitis virus (MHV; m-β-CoV) serves as a useful model for studying the cellular factors involved in neuroinflammation. To understand the role of matrix metalloproteinases (MMPs) in neuroinflammation, brain tissues from m-β-CoV-infected mice were harvested at different days post-infection (d.p.i) and investigated for Mmp expression by RT-qPCR. Mmp-2, -3, -8, -12 showed significant mRNA upregulation peaking with viral replication between 5 and 6 d.p.i. Elevated levels of MMP regulator TIMP-1 are suggestive of a TIMP-1 mediated host antiviral response. Biological network assessment suggested a direct involvement of MMP-3, -8, -14 in facilitating peripheral leukocyte infiltrations. Flow cytometry confirmed the increased presence of NK cells, CD4+ and CD8+ T cells, neutrophils, and MHCII expressing cells in the m-β-CoV infected mice brain. Our study revealed that m-β-CoV upregulated Park7, RelA, Nrf2, and Hmox1 transcripts involved in ROS production and antioxidant pathways, describing the possible nexus between oxidative pathways, MMPs, and TIMP in m-β-CoV-induced neuroinflammation.
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Affiliation(s)
- Sourodip Sengupta
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata (IISER-K), Mohanpur, India
| | - Sankar Addya
- Department of Cancer Biology, Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, USA
| | - Diptomit Biswas
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata (IISER-K), Mohanpur, India
| | - Paromita Banerjee
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata (IISER-K), Mohanpur, India
| | - Jayasri Das Sarma
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata (IISER-K), Mohanpur, India,Corresponding author
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8
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Natural and Recombinant SARS-CoV-2 Isolates Rapidly Evolve In Vitro to Higher Infectivity through More Efficient Binding to Heparan Sulfate and Reduced S1/S2 Cleavage. J Virol 2021; 95:e0135721. [PMID: 34406867 PMCID: PMC8513475 DOI: 10.1128/jvi.01357-21] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
One of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virulence factors is the ability to interact with high affinity to the ACE2 receptor, which mediates viral entry into cells. The results of our study demonstrate that within a few passages in cell culture, both the natural isolate of SARS-CoV-2 and the recombinant cDNA-derived variant acquire an additional ability to bind to heparan sulfate (HS). This promotes a primary attachment of viral particles to cells before their further interactions with the ACE2. Interaction with HS is acquired through multiple mechanisms. These include (i) accumulation of point mutations in the N-terminal domain (NTD) of the S protein, which increases the positive charge of the surface of this domain, (ii) insertions into the NTD of heterologous peptides containing positively charged amino acids, and (iii) mutation of the first amino acid downstream of the furin cleavage site. This last mutation affects S protein processing, transforms the unprocessed furin cleavage site into the heparin-binding peptide, and makes viruses less capable of syncytium formation. These viral adaptations result in higher affinity of viral particles to heparin, dramatic increase in plaque sizes, more efficient viral spread, higher infectious titers, and 2 orders of magnitude higher infectivity. The detected adaptations also suggest an active role of NTD in virus attachment and entry. As in the case of other RNA-positive (RNA+) viruses, evolution to HS binding may result in virus attenuation in vivo. IMPORTANCE The spike protein of SARS-CoV-2 is a major determinant of viral pathogenesis. It mediates binding to the ACE2 receptor and, later, fusion of viral envelope and cellular membranes. The results of our study demonstrate that SARS-CoV-2 rapidly evolves during propagation in cultured cells. Its spike protein acquires mutations in the NTD and in the P1′ position of the furin cleavage site (FCS). The amino acid substitutions or insertions of short peptides in NTD are closely located on the protein surface and increase its positive charge. They strongly increase affinity of the virus to heparan sulfate, make it dramatically more infectious for the cultured cells, and decrease the genome equivalent to PFU (GE/PFU) ratio by orders of magnitude. The S686G mutation also transforms the FCS into the heparin-binding peptide. Thus, the evolved SARS-CoV-2 variants efficiently use glycosaminoglycans on the cell surface for primary attachment before the high-affinity interaction of the spikes with the ACE2 receptor.
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9
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Cell Entry of Animal Coronaviruses. Viruses 2021; 13:v13101977. [PMID: 34696406 PMCID: PMC8540712 DOI: 10.3390/v13101977] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 09/22/2021] [Accepted: 09/23/2021] [Indexed: 01/11/2023] Open
Abstract
Coronaviruses (CoVs) are a group of enveloped positive-sense RNA viruses and can cause deadly diseases in animals and humans. Cell entry is the first and essential step of successful virus infection and can be divided into two ongoing steps: cell binding and membrane fusion. Over the past two decades, stimulated by the global outbreak of SARS-CoV and pandemic of SARS-CoV-2, numerous efforts have been made in the CoV research. As a result, significant progress has been achieved in our understanding of the cell entry process. Here, we review the current knowledge of this essential process, including the viral and host components involved in cell binding and membrane fusion, molecular mechanisms of their interactions, and the sites of virus entry. We highlight the recent findings of host restriction factors that inhibit CoVs entry. This knowledge not only enhances our understanding of the cell entry process, pathogenesis, tissue tropism, host range, and interspecies-transmission of CoVs but also provides a theoretical basis to design effective preventive and therapeutic strategies to control CoVs infection.
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10
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Stout AE, Millet JK, Stanhope MJ, Whittaker GR. Furin cleavage sites in the spike proteins of bat and rodent coronaviruses: Implications for virus evolution and zoonotic transfer from rodent species. One Health 2021; 13:100282. [PMID: 34179330 PMCID: PMC8216856 DOI: 10.1016/j.onehlt.2021.100282] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 06/16/2021] [Indexed: 12/02/2022] Open
Abstract
Bats and rodents comprise two of the world's largest orders of mammals and the order Chiroptera (bats) has been implicated as a major reservoir of coronaviruses in nature and a source of zoonotic transfer to humans. However, the order Rodentia (rodents) also harbors coronaviruses, with two human coronaviruses (HCoV-OC43 and HCoV-HKU1) considered to have rodent origins. The coronavirus spike protein mediates viral entry and is a major determinant of viral tropism; importantly, the spike protein is activated by host cell proteases at two distinct sites, designated as S1/S2 and S2’. SARS-CoV-2, which is considered to be of bat origin, contains a cleavage site for the protease furin at S1/S2, absent from the rest of the currently known betacoronavirus lineage 2b coronaviruses (Sarbecoviruses). This cleavage site is thought to be critical to its replication and pathogenesis, with a notable link to virus transmission. Here, we examine the spike protein across coronaviruses identified in both bat and rodent species and address the role of furin as an activating protease. Utilizing two publicly available furin prediction algorithms (ProP and PiTou) and based on spike sequences reported in GenBank, we show that the S1/S2 furin cleavage site is typically not present in bat virus spike proteins but is common in rodent-associated sequences, and suggest this may have implications for zoonotic transfer. We provide a phylogenetic history of the Embecoviruses (betacoronavirus lineage 2a), including context for the use of furin as an activating protease for the viral spike protein. From a One Health perspective, continued rodent surveillance should be an important consideration in uncovering novel circulating coronaviruses.
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Affiliation(s)
- Alison E Stout
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY, USA
| | - Jean K Millet
- Université Paris-Saclay, INRAE, UVSQ, Virologie et Immunologie Moléculaires, 78352, Jouy-en-Josas, France
| | - Michael J Stanhope
- Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Gary R Whittaker
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY, USA.,Master of Public Health Program, Cornell University, Ithaca, NY, USA
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11
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Yan W, Qiu R, Wang F, Fu X, Li H, Cui P, Zhai Y, Li C, Zhang L, Gu K, Zuo L, Lei C, Wang H, Yang X. Genetic and pathogenic characterization of a novel recombinant avian infectious bronchitis virus derived from GI-1, GI-13, GI-28, and GI-19 strains in Southwestern China. Poult Sci 2021; 100:101210. [PMID: 34116353 PMCID: PMC8192866 DOI: 10.1016/j.psj.2021.101210] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 04/08/2021] [Accepted: 04/09/2021] [Indexed: 11/19/2022] Open
Abstract
Avian infectious bronchitis (IB), caused by avian infectious bronchitis virus (IBV), is an acute and highly contagious disease that is extremely harmful to the poultry industry throughout the world. The cross-using of different attenuated live vaccine strains has led to the occurrence of diverse IBV serotypes. In this study, we isolated an IBV strain from a chicken farm in southwest China and designated it CK/CH/SCMY/160315. Construction of a phylogenetic tree based on full S1 gene sequence analysis suggested that CK/CH/SCMY/160315 bears similarity to GI-28, and further comparison of S1 amino acid residues revealed that CK/CH/SCMY/160315 showed mutations and deletions in many key positions between LDT3-A and other GI-28 reference strains. Importantly, CK/CH/SCMY/160315 was identified as a novel recombinant virus derived from live attenuated vaccine strains H120 (GI-1), 4/91 (GI-13), LDT3-A (GI-28), and the field strain LJL/08-1 (GI-19), identifying at least 5 recombination sites in both structural and accessory genes. Pathogenicity analysis indicated that CK/CH/SCMY/160315 caused listlessness, sneezing, huddling, head shaking, and increased antibody levels in the inoculated chickens. To further describe pathogenicity of this novel strain, we assessed viral load in different tissues and conducted hematoxylin and eosin (HE) staining of the trachea, lungs and kidneys. Our results provide evidence for the continuing evolution of IBV field strains via genetic recombination and mutation, leading to outbreaks in the vaccinated chicken populations in China.
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Affiliation(s)
- Wenjun Yan
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Rongbin Qiu
- College of Life Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China
| | - Fuyan Wang
- Sichuan Sundaily Farm Ecological Food Co., Ltd., Mianyang 621010, China
| | - Xue Fu
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Hao Li
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Pengfei Cui
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Yaru Zhai
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Chun Li
- Sichuan Animal Disease Control Center, Chengdu, 610041, China
| | - Lan Zhang
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Kui Gu
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Lei Zuo
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Changwei Lei
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Hongning Wang
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China
| | - Xin Yang
- Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province; Key Laboratory of Bio-Resources and Eco-Environment, Ministry of Education, College of Life Science Sichuan University, Chengdu 610064, China.
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12
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Potential differences in cleavage of the S protein and type-1 interferon together control human coronavirus infection, propagation, and neuropathology within the central nervous system. J Virol 2021; 95:JVI.00140-21. [PMID: 33627397 PMCID: PMC8139659 DOI: 10.1128/jvi.00140-21] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Human coronaviruses (HCoV) are respiratory pathogens which have been known since the 1960's. In December 2019, a new betacoronavirus, SARS-CoV-2, was reported and is responsible for one of the biggest pandemics of the last two centuries. Similar to the HCoV-OC43 strain, available evidence suggests SARS-CoV-2 neuroinvasion associated with potential neurological disorders. Coronavirus infection of the central nervous system (CNS) is largely controlled by a viral factor, the spike glycoprotein (S) and a host factor, innate immunity. However, the interaction between these two factors remains elusive. Proteolytic cleavage of the S protein can occur at the interface between receptor binding (S1) and fusion (S2) domains (S1/S2), as well as in a position adjacent to a fusion peptide within S2 (S2'). Herein, using HCoV-OC43 as a surrogate for SARS-CoV-2, we report that both S protein sites are involved in neurovirulence and are required for optimal CNS infection. Whereas efficient cleavage at S1/S2 is associated with decreased virulence, the potentially cleavable putative S2' site is essential for efficient viral infection. Furthermore, type 1 interferon (IFN 1)-related innate immunity also plays an important role in the control of viral spread towards the spinal cord, by preventing infection of ependymal cells. Our results underline the link between the differential S cleavage and IFN 1 in the prevention of viral spread, to control the severity of infection and pathology in both immunocompetent and immunodeficient mice. Taken together, these results point towards two potential therapeutic anti-viral targets: cleavage of the S protein in conjunction with efficient IFN 1-related innate immunity to prevent or at least reduce neuroinvasion, neural spread, and potential associated neurovirulence of human coronaviruses.ImportanceHuman coronaviruses (HCoV) are recognized respiratory pathogens. The emergence of the novel pathogenic member of this family in December 2019 (SARS-CoV-2, which causes COVID-19) poses a global health emergency. As with other coronaviruses reported previously, invasion of the human central nervous system (CNS), associated with diverse neurological disorders, was suggested for SARS-CoV-2. Herein, using the related HCoV-OC43 strain, we show that the viral spike protein constitutes a major neurovirulence factor and that type 1 interferon (IFN 1), in conjunction with cleavage of S protein by host proteases, represent important host factors that participate in the control of CNS infection.To our knowledge, this is the first demonstration of a direct link between cleavage of the S protein, innate immunity and neurovirulence. Understanding mechanisms of viral infection and spread in neuronal cells is essential to better design therapeutic strategies, and to prevent infection by human coronaviruses such as SARS-CoV-2 in human CNS especially in the vulnerable populations such as the elderly and immune-compromised individuals.
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13
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SARS-CoV-2 induces double-stranded RNA-mediated innate immune responses in respiratory epithelial-derived cells and cardiomyocytes. Proc Natl Acad Sci U S A 2021; 118:2022643118. [PMID: 33811184 PMCID: PMC8072330 DOI: 10.1073/pnas.2022643118] [Citation(s) in RCA: 130] [Impact Index Per Article: 43.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
SARS-CoV-2 emergence in late 2019 led to the COVID-19 pandemic that has had devastating effects on human health and the economy. While early innate immune responses are essential for protection against virus invasion and inadequate responses are associated with severe COVID-19 disease, gaps remain in our knowledge about the interaction of SARS-CoV-2 with host antiviral pathways. We characterized the innate immune response to SARS-CoV-2 in relevant respiratory tract-derived cells and cardiomyocytes and found that SARS-CoV-2 activates two antiviral pathways, oligoadenylate synthetase–ribonuclease L and protein kinase R, while inducing minimal levels of interferon. This is in contrast to Middle East respiratory syndrome-CoV, which inhibits all three pathways. Activation of these pathways may contribute to the distinctive pathogenesis of SARS-CoV-2. Coronaviruses are adept at evading host antiviral pathways induced by viral double-stranded RNA, including interferon (IFN) signaling, oligoadenylate synthetase–ribonuclease L (OAS-RNase L), and protein kinase R (PKR). While dysregulated or inadequate IFN responses have been associated with severe coronavirus infection, the extent to which the recently emerged SARS-CoV-2 activates or antagonizes these pathways is relatively unknown. We found that SARS-CoV-2 infects patient-derived nasal epithelial cells, present at the initial site of infection; induced pluripotent stem cell-derived alveolar type 2 cells (iAT2), the major cell type infected in the lung; and cardiomyocytes (iCM), consistent with cardiovascular consequences of COVID-19 disease. Robust activation of IFN or OAS-RNase L is not observed in these cell types, whereas PKR activation is evident in iAT2 and iCM. In SARS-CoV-2–infected Calu-3 and A549ACE2 lung-derived cell lines, IFN induction remains relatively weak; however, activation of OAS-RNase L and PKR is observed. This is in contrast to Middle East respiratory syndrome (MERS)-CoV, which effectively inhibits IFN signaling and OAS-RNase L and PKR pathways, but is similar to mutant MERS-CoV lacking innate immune antagonists. Remarkably, OAS-RNase L and PKR are activated in MAVS knockout A549ACE2 cells, demonstrating that SARS-CoV-2 can induce these host antiviral pathways despite minimal IFN production. Moreover, increased replication and cytopathic effect in RNASEL knockout A549ACE2 cells implicates OAS-RNase L in restricting SARS-CoV-2. Finally, while SARS-CoV-2 fails to antagonize these host defense pathways, which contrasts with other coronaviruses, the IFN signaling response is generally weak. These host–virus interactions may contribute to the unique pathogenesis of SARS-CoV-2.
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14
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Chen C, Chou Y, Hsueh Y. SARS-CoV-2 D614 and G614 spike variants impair neuronal synapses and exhibit differential fusion ability.. [PMID: 0 DOI: 10.1101/2020.12.03.409763] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
AbstractSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes Coronavirus disease 2019 (COVID-19) exhibits two major variants based on mutations of its spike protein, i.e., the D614 prototype and G614 variant. Although neurological symptoms have been frequently reported in patients, it is still unclear whether SARS-CoV-2 impairs neuronal activity or function. Here, we show that expression of both D614 and G614 spike proteins is sufficient to induce phenotypes of impaired neuronal morphology, including defective dendritic spines and shortened dendritic length. Using spike protein-specific monoclonal antibodies, we found that D614 and G614 spike proteins show differential S1/S2 cleavage and cell fusion efficiency. Our findings provide an explanation for higher transmission of the G614 variant and the neurological manifestations observed in COVID-19 patients.
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15
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Schütz D, Ruiz-Blanco YB, Münch J, Kirchhoff F, Sanchez-Garcia E, Müller JA. Peptide and peptide-based inhibitors of SARS-CoV-2 entry. Adv Drug Deliv Rev 2020; 167:47-65. [PMID: 33189768 PMCID: PMC7665879 DOI: 10.1016/j.addr.2020.11.007] [Citation(s) in RCA: 112] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 11/08/2020] [Accepted: 11/10/2020] [Indexed: 12/18/2022]
Abstract
To date, no effective vaccines or therapies are available against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative pandemic agent of the coronavirus disease 2019 (COVID-19). Due to their safety, efficacy and specificity, peptide inhibitors hold great promise for the treatment of newly emerging viral pathogens. Based on the known structures of viral proteins and their cellular targets, antiviral peptides can be rationally designed and optimized. The resulting peptides may be highly specific for their respective targets and particular viral pathogens or exert broad antiviral activity. Here, we summarize the current status of peptides inhibiting SARS-CoV-2 entry and outline the strategies used to design peptides targeting the ACE2 receptor or the viral spike protein and its activating proteases furin, transmembrane serine protease 2 (TMPRSS2), or cathepsin L. In addition, we present approaches used against related viruses such as SARS-CoV-1 that might be implemented for inhibition of SARS-CoV-2 infection.
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Affiliation(s)
- Desiree Schütz
- Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany
| | - Yasser B Ruiz-Blanco
- Computational Biochemistry, Center of Medical Biotechnology, University of Duisburg-Essen, 45117 Essen, Germany
| | - Jan Münch
- Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany
| | - Frank Kirchhoff
- Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany
| | - Elsa Sanchez-Garcia
- Computational Biochemistry, Center of Medical Biotechnology, University of Duisburg-Essen, 45117 Essen, Germany.
| | - Janis A Müller
- Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany.
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16
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Milewska A, Falkowski K, Kulczycka M, Bielecka E, Naskalska A, Mak P, Lesner A, Ochman M, Urlik M, Diamandis E, Prassas I, Potempa J, Kantyka T, Pyrc K. Kallikrein 13 serves as a priming protease during infection by the human coronavirus HKU1. Sci Signal 2020; 13:13/659/eaba9902. [PMID: 33234691 PMCID: PMC7857416 DOI: 10.1126/scisignal.aba9902] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Unlike SARS-CoV-2, the human coronavirus HKU1 normally causes relatively mild respiratory tract infections; however, it shares with SARS-CoV-2 the mechanism of using its surface spike (S) protein to enter target cells. Because the host receptor for HCoV-HKU1 is unknown, efforts to study the virus in cell culture systems have proved difficult. Milewska et al. found that knockout of the protease kallikrein 13 (KLK13) in human airway epithelial cells blocked their infection by HCoV-HKU1, that overexpression of KLK13 in nonpermissive cells enabled their infection by the virus, and that KLK13 cleaved the viral S protein. Together, these findings suggest that KLK13 is a priming enzyme for viral entry and may help to establish cell lines that can facilitate further investigation of the mechanism of viral pathogenesis. Human coronavirus HKU1 (HCoV-HKU1) is associated with respiratory disease and is prevalent worldwide, but an in vitro model for viral replication is lacking. An interaction between the coronaviral spike (S) protein and its receptor is the primary determinant of tissue and host specificity; however, viral entry is a complex process requiring the concerted action of multiple cellular elements. Here, we found that the protease kallikrein 13 (KLK13) was required for the infection of human respiratory epithelial cells and was sufficient to mediate the entry of HCoV-HKU1 into nonpermissive RD cells. We also demonstrated the cleavage of the HCoV-HKU1 S protein by KLK13 in the S1/S2 region, suggesting that KLK13 is the priming enzyme for this virus. Together, these data suggest that protease distribution and specificity determine the tissue and cell specificity of the virus and may also regulate interspecies transmission.
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Affiliation(s)
- Aleksandra Milewska
- Virogenetics Laboratory of Virology, Malopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7a, 30-387 Krakow, Poland.,Microbiology Department, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland
| | - Katherine Falkowski
- Microbiology Department, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland
| | - Magdalena Kulczycka
- Laboratory of Proteolysis and Post-translational Modification of Proteins, Malopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland
| | - Ewa Bielecka
- Laboratory of Proteolysis and Post-translational Modification of Proteins, Malopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland
| | - Antonina Naskalska
- Virogenetics Laboratory of Virology, Malopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7a, 30-387 Krakow, Poland
| | - Pawel Mak
- Department of Analytical Biochemistry, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7 St., 30-387 Krakow, Poland
| | - Adam Lesner
- Faculty of Chemistry, University of Gdansk, Wita Stwosza 63, 80-308 Gdansk, Poland
| | - Marek Ochman
- Department of Cardiac, Vascular and Endovascular Surgery and Transplantology, Medical University of Silesia in Katowice, Silesian Centre for Heart Diseases, Zabrze, Poland
| | - Maciej Urlik
- Department of Cardiac, Vascular and Endovascular Surgery and Transplantology, Medical University of Silesia in Katowice, Silesian Centre for Heart Diseases, Zabrze, Poland
| | - Elftherios Diamandis
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada.,Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada.,Department of Clinical Biochemistry, University Health Network, Toronto, Canada.,Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada
| | - Ioannis Prassas
- Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada.,Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada
| | - Jan Potempa
- Microbiology Department, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland.,Centre for Oral Health and Systemic Diseases, University of Louisville School of Dentistry, Louisville, KY 40202, USA
| | - Tomasz Kantyka
- Laboratory of Proteolysis and Post-translational Modification of Proteins, Malopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland.,Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, 5020 Bergen, Norway
| | - Krzysztof Pyrc
- Virogenetics Laboratory of Virology, Malopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7a, 30-387 Krakow, Poland.
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17
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Li Y, Renner DM, Comar CE, Whelan JN, Reyes HM, Cardenas-Diaz FL, Truitt R, Tan LH, Dong B, Alysandratos KD, Huang J, Palmer JN, Adappa ND, Kohanski MA, Kotton DN, Silverman RH, Yang W, Morrisey E, Cohen NA, Weiss SR. SARS-CoV-2 induces double-stranded RNA-mediated innate immune responses in respiratory epithelial derived cells and cardiomyocytes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2020. [PMID: 32995797 DOI: 10.1101/2020.09.24.312553] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Coronaviruses are adept at evading host antiviral pathways induced by viral double-stranded RNA, including interferon (IFN) signaling, oligoadenylate synthetase-ribonuclease L (OAS-RNase L), and protein kinase R (PKR). While dysregulated or inadequate IFN responses have been associated with severe coronavirus infection, the extent to which the recently emerged SARS-CoV-2 activates or antagonizes these pathways is relatively unknown. We found that SARS-CoV-2 infects patient-derived nasal epithelial cells, present at the initial site of infection, induced pluripotent stem cell-derived alveolar type 2 cells (iAT2), the major cell type infected in the lung, and cardiomyocytes (iCM), consistent with cardiovascular consequences of COVID-19 disease. Robust activation of IFN or OAS-RNase L is not observed in these cell types, while PKR activation is evident in iAT2 and iCM. In SARS-CoV-2 infected Calu-3 and A549 ACE2 lung-derived cell lines, IFN induction remains relatively weak; however activation of OAS-RNase L and PKR is observed. This is in contrast to MERS-CoV, which effectively inhibits IFN signaling as well as OAS-RNase L and PKR pathways, but similar to mutant MERS-CoV lacking innate immune antagonists. Remarkably, both OAS-RNase L and PKR are activated in MAVS knockout A549 ACE2 cells, demonstrating that SARS-CoV-2 can induce these host antiviral pathways despite minimal IFN production. Moreover, increased replication and cytopathic effect in RNASEL knockout A549 ACE2 cells implicates OAS-RNase L in restricting SARS-CoV-2. Finally, while SARS-CoV-2 fails to antagonize these host defense pathways, which contrasts with other coronaviruses, the IFN signaling response is generally weak. These host-virus interactions may contribute to the unique pathogenesis of SARS-CoV-2. Significance SARS-CoV-2 emergence in late 2019 led to the COVID-19 pandemic that has had devastating effects on human health and the economy. Early innate immune responses are essential for protection against virus invasion. While inadequate innate immune responses are associated with severe COVID-19 diseases, understanding of the interaction of SARS-CoV-2 with host antiviral pathways is minimal. We have characterized the innate immune response to SARS-CoV-2 infections in relevant respiratory tract derived cells and cardiomyocytes and found that SARS-CoV-2 activates two antiviral pathways, oligoadenylate synthetase-ribonuclease L (OAS-RNase L), and protein kinase R (PKR), while inducing minimal levels of interferon. This in contrast to MERS-CoV which inhibits all three pathways. Activation of these pathways may contribute to the distinctive pathogenesis of SARS-CoV-2.
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18
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The Amino Acid at Position 8 of the Proteolytic Cleavage Site of the Mumps Virus Fusion Protein Affects Viral Proteolysis and Fusogenicity. J Virol 2020; 94:JVI.01732-20. [PMID: 32907974 DOI: 10.1128/jvi.01732-20] [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: 09/01/2020] [Accepted: 09/02/2020] [Indexed: 11/20/2022] Open
Abstract
The mumps virus (MuV) fusion protein (F) plays a crucial role for the entry process and spread of infection by mediating fusion between viral and cellular membranes as well as between infected and neighboring cells, respectively. The fusogenicity of MuV differs depending on the strain and might correlate with the virulence; however, it is unclear which mechanisms contribute to the differentiated fusogenicity. The cleavage motif of MuV F is highly conserved among all strains, except the amino acid residue at position 8 (P8) that shows a certain variability with a total of four amino acid variants (leucine [L], proline [P], serine [S], and threonine [T]). We demonstrate that P8 affects the proteolytic processing and the fusogenicity of MuV F. The presence of L or S at P8 resulted in a slower proteolysis of MuV F by furin and a reduced ability to mediate cell-cell fusion. However, virus-cell fusion was more efficient for F proteins harboring L or S at P8, suggesting that P8 contributes to the mechanism of viral spread: P and T enable a rapid spread of infection by cell-to-cell fusion, whereas viruses harboring L or S at P8 spread preferentially by the release of infectious viral particles. Our study provides novel insights into the fusogenicity of MuV and its influence on the mechanisms of virus spread within infected tissues. Assuming a correlation between MuV fusogenicity and virulence, sequence information on the amino acid residue at P8 might be helpful to estimate the virulence of circulating and emerging strains.IMPORTANCE Mumps virus (MuV) is the causative agent of the highly infectious disease mumps. Mumps is mainly associated with mild symptoms, but severe complications such as encephalitis, meningitis, or orchitis can also occur. There is evidence that the virulence of different MuV strains and variants might correlate with the ability of the fusion protein (F) to mediate cell-to-cell fusion. However, the relation between virulence and fusogenicity or the mechanisms responsible for the varied fusogenicity of different MuV strains are incompletely understood. Here, we focused on the amino acid residue at position 8 (P8) of the proteolytic cleavage site of MuV F, because this amino acid residue shows a striking variability depending on the genotype of MuV. The P8 residue has a significant effect on the proteolytic processing and fusogenicity of MuV F and might thereby determine the route of viral spread within infected tissues.
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19
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Berrio A, Gartner V, Wray GA. Positive selection within the genomes of SARS-CoV-2 and other Coronaviruses independent of impact on protein function. PeerJ 2020; 8:e10234. [PMID: 33088633 PMCID: PMC7571416 DOI: 10.7717/peerj.10234] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 10/04/2020] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND The emergence of a novel coronavirus (SARS-CoV-2) associated with severe acute respiratory disease (COVID-19) has prompted efforts to understand the genetic basis for its unique characteristics and its jump from non-primate hosts to humans. Tests for positive selection can identify apparently nonrandom patterns of mutation accumulation within genomes, highlighting regions where molecular function may have changed during the origin of a species. Several recent studies of the SARS-CoV-2 genome have identified signals of conservation and positive selection within the gene encoding Spike protein based on the ratio of synonymous to nonsynonymous substitution. Such tests cannot, however, detect changes in the function of RNA molecules. METHODS Here we apply a test for branch-specific oversubstitution of mutations within narrow windows of the genome without reference to the genetic code. RESULTS We recapitulate the finding that the gene encoding Spike protein has been a target of both purifying and positive selection. In addition, we find other likely targets of positive selection within the genome of SARS-CoV-2, specifically within the genes encoding Nsp4 and Nsp16. Homology-directed modeling indicates no change in either Nsp4 or Nsp16 protein structure relative to the most recent common ancestor. These SARS-CoV-2-specific mutations may affect molecular processes mediated by the positive or negative RNA molecules, including transcription, translation, RNA stability, and evasion of the host innate immune system. Our results highlight the importance of considering mutations in viral genomes not only from the perspective of their impact on protein structure, but also how they may impact other molecular processes critical to the viral life cycle.
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Affiliation(s)
| | - Valerie Gartner
- Department of Biology, Duke University, Durham, NC, USA
- University Program in Genetics and Genomics, Duke University, Durham, NC, USA
| | - Gregory A. Wray
- Department of Biology, Duke University, Durham, NC, USA
- Center for Genomic and Computational Biology, Duke University, Durham, NC, USA
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20
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Adhikari B, Marasini BP, Rayamajhee B, Bhattarai BR, Lamichhane G, Khadayat K, Adhikari A, Khanal S, Parajuli N. Potential roles of medicinal plants for the treatment of viral diseases focusing on COVID-19: A review. Phytother Res 2020; 35:1298-1312. [PMID: 33037698 PMCID: PMC7675695 DOI: 10.1002/ptr.6893] [Citation(s) in RCA: 117] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 07/16/2020] [Accepted: 09/16/2020] [Indexed: 12/18/2022]
Abstract
The whole world is entangled by the coronavirus disease (COVID‐19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), people are dying in thousands each day, and without an actual medication, it seems not possible for the bringing this global health crisis to a stop. Natural products have been in constant use since ancient times and are proven by time to be effective. Crude extract or pure compounds isolated from medicinal plants and/or herbs such as Artemisia annua, Agastache rugosa, Astragalus membranaceus, Cassia alata, Ecklonia cava, Gymnema sylvestre, Glycyrrhizae uralensis, Houttuynia cordata, Lindera aggregata, Lycoris radiata, Mollugo cerviana, Polygonum multiflorum, Pyrrosia lingua, Saposhnikoviae divaricate, Tinospora cordifolia etc. have shown promising inhibitory effect against coronavirus. Several molecules, including acacetin, amentoflavone, allicin, blancoxanthone, curcumin, daidzein, diosmin, epigallocatechin‐gallate, emodin, hesperidin, herbacetin, hirsutenone, iguesterin, jubanine G, kaempferol, lycorine, pectolinarin, phloroeckol, silvestrol, tanshinone I, taxifolin, rhoifolin, xanthoangelol E, zingerol etc. isolated from plants could also be potential drug candidates against COVID‐19. Moreover, these could also show promising inhibitory effects against influenza‐parainfluenza viruses, respiratory syncytial virus, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome coronavirus (MERS‐CoV). Here, we have reported 93 antiviral drug candidates which could be a potential area of research in drug discovery.
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Affiliation(s)
- Bikash Adhikari
- Central Department of Chemistry, Tribhuvan University, Kirtipur, Nepal
| | - Bishnu P Marasini
- Department of Biotechnology, National College, Tribhuvan University, Kirtipur, Nepal
| | - Binod Rayamajhee
- School of Optometry and Vision Science, Faculty of Science, University of New South Wales (UNSW), Sydney, Australia.,Department of Infection and Immunology, Kathmandu Research Institute for Biological Sciences (KRIBS), Lalitpur, Nepal
| | | | - Ganesh Lamichhane
- Central Department of Chemistry, Tribhuvan University, Kirtipur, Nepal
| | - Karan Khadayat
- Central Department of Chemistry, Tribhuvan University, Kirtipur, Nepal.,Department of Biotechnology, National College, Tribhuvan University, Kirtipur, Nepal
| | - Achyut Adhikari
- Central Department of Chemistry, Tribhuvan University, Kirtipur, Nepal
| | - Santosh Khanal
- Department of Biotechnology, National College, Tribhuvan University, Kirtipur, Nepal
| | - Niranjan Parajuli
- Central Department of Chemistry, Tribhuvan University, Kirtipur, Nepal
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21
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Hartenian E, Nandakumar D, Lari A, Ly M, Tucker JM, Glaunsinger BA. The molecular virology of coronaviruses. J Biol Chem 2020; 295:12910-12934. [PMID: 32661197 PMCID: PMC7489918 DOI: 10.1074/jbc.rev120.013930] [Citation(s) in RCA: 302] [Impact Index Per Article: 75.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 07/13/2020] [Indexed: 12/14/2022] Open
Abstract
Few human pathogens have been the focus of as much concentrated worldwide attention as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of COVID-19. Its emergence into the human population and ensuing pandemic came on the heels of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), two other highly pathogenic coronavirus spillovers, which collectively have reshaped our view of a virus family previously associated primarily with the common cold. It has placed intense pressure on the collective scientific community to develop therapeutics and vaccines, whose engineering relies on a detailed understanding of coronavirus biology. Here, we present the molecular virology of coronavirus infection, including its entry into cells, its remarkably sophisticated gene expression and replication mechanisms, its extensive remodeling of the intracellular environment, and its multifaceted immune evasion strategies. We highlight aspects of the viral life cycle that may be amenable to antiviral targeting as well as key features of its biology that await discovery.
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Affiliation(s)
- Ella Hartenian
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| | - Divya Nandakumar
- Department of Plant and Microbial Biology, University of California, Berkeley, California, USA
| | - Azra Lari
- Department of Plant and Microbial Biology, University of California, Berkeley, California, USA
| | - Michael Ly
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
| | - Jessica M Tucker
- Department of Plant and Microbial Biology, University of California, Berkeley, California, USA
| | - Britt A Glaunsinger
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA; Department of Plant and Microbial Biology, University of California, Berkeley, California, USA; Howard Hughes Medical Institute, University of California, Berkeley, California, USA.
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22
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Broad and Differential Animal Angiotensin-Converting Enzyme 2 Receptor Usage by SARS-CoV-2. J Virol 2020; 94:JVI.00940-20. [PMID: 32661139 PMCID: PMC7459545 DOI: 10.1128/jvi.00940-20] [Citation(s) in RCA: 119] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 07/06/2020] [Indexed: 01/16/2023] Open
Abstract
SARS-CoV-2 uses human ACE2 as a primary receptor for host cell entry. Viral entry mediated by the interaction of ACE2 with spike protein largely determines host range and is the major constraint to interspecies transmission. We examined the receptor activity of 14 ACE2 orthologs and found that wild-type and mutant SARS-CoV-2 lacking the furin cleavage site in S protein could utilize ACE2 from a broad range of animal species to enter host cells. These results have important implications in the natural hosts, interspecies transmission, animal models, and molecular basis of receptor binding for SARS-CoV-2. The COVID-19 pandemic has caused an unprecedented global public health and economic crisis. The origin and emergence of its causal agent, SARS-CoV-2, in the human population remains mysterious, although bat and pangolin were proposed to be the natural reservoirs. Strikingly, unlike the SARS-CoV-2-like coronaviruses (CoVs) identified in bats and pangolins, SARS-CoV-2 harbors a polybasic furin cleavage site in its spike (S) glycoprotein. SARS-CoV-2 uses human angiotensin-converting enzyme 2 (ACE2) as its receptor to infect cells. Receptor recognition by the S protein is the major determinant of host range, tissue tropism, and pathogenesis of coronaviruses. In an effort to search for the potential intermediate or amplifying animal hosts of SARS-CoV-2, we examined receptor activity of ACE2 from 14 mammal species and found that ACE2s from multiple species can support the infectious entry of lentiviral particles pseudotyped with the wild-type or furin cleavage site-deficient S protein of SARS-CoV-2. ACE2 of human/rhesus monkey and rat/mouse exhibited the highest and lowest receptor activities, respectively. Among the remaining species, ACE2s from rabbit and pangolin strongly bound to the S1 subunit of SARS-CoV-2 S protein and efficiently supported the pseudotyped virus infection. These findings have important implications for understanding potential natural reservoirs, zoonotic transmission, human-to-animal transmission, and use of animal models. IMPORTANCE SARS-CoV-2 uses human ACE2 as a primary receptor for host cell entry. Viral entry mediated by the interaction of ACE2 with spike protein largely determines host range and is the major constraint to interspecies transmission. We examined the receptor activity of 14 ACE2 orthologs and found that wild-type and mutant SARS-CoV-2 lacking the furin cleavage site in S protein could utilize ACE2 from a broad range of animal species to enter host cells. These results have important implications in the natural hosts, interspecies transmission, animal models, and molecular basis of receptor binding for SARS-CoV-2.
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Adeoye AO, Oso BJ, Olaoye IF, Tijjani H, Adebayo AI. Repurposing of chloroquine and some clinically approved antiviral drugs as effective therapeutics to prevent cellular entry and replication of coronavirus. J Biomol Struct Dyn 2020; 39:3469-3479. [PMID: 32375574 PMCID: PMC7232887 DOI: 10.1080/07391102.2020.1765876] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The reemergence of coronavirus prompts the need for the development of effective therapeutics to prevent the cellular entry and replication of coronavirus. This study demonstrated the putative inhibitory potential of lopinavir, remdesivir, oseltamir, azithromycin, ribavirin, and chloroquine towards V-ATPase, protein kinase A, SARS-CoV spike glycoprotein/ACE-2 complex and viral proteases. The pharmacodynamic and pharmacokinetic properties were predicted through the pkCSM server while the corresponding binding affinity of the selected drugs towards the proteins was computed using AutodockVina Screening tool. The ADMET properties revealed all the drugs possess drug-like properties. Lopinavir has the highest binding affinities to the pocket site of SARS-CoV spike glycoprotein/ACE-2 complex, cyclic AMP-dependent protein kinase A and 3-Chymotrypsin like protease while redemsivir has the highest binding affinities for vacuolar proton-translocating ATPase (V-ATPase) and papain-like proteins. The amino acids Asp269, Leu370, His374, and His345 were predicted as the key residues for lopinavir binding to human SARS-CoV spike glycoprotein/ACE-2 complex while His378, Tyr515, Leu73, Leu100, Phe32 and Phe40 for remdesivir and Tyr510, Phe504, Met62, Tyr50, and His378 were predicted for azithromycin as the key residues for binding to SARS-CoV spike glycoprotein/ACE-2 complex. Moreover, it was also observed that chloroquine has appreciable binding affinities for 3-Chymotrpsin- like protease and cyclic AMP-dependent protein kinase A when compared to Oseltamivir and ribavirin. The study provided evidence suggesting putative repurposing of the selected drugs for the development of valuable drugs for the prevention of cellular entry and replication of coronavirus. Communicated by Ramaswamy H. Sarma
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Affiliation(s)
- Akinwunmi O Adeoye
- Department of Biochemistry, Federal University Oye-Ekiti, Oye-Ekiti, Nigeria
| | | | - Ige Francis Olaoye
- Department of Biochemistry, McPherson University, Seriki Sotayo, Nigeria
| | - Habibu Tijjani
- Department of Biochemistry, Natural Product Research Laboratory, Bauchi State University, Gadau, Nigeria
| | - Ahmed I Adebayo
- Department of Biochemistry, University of Ilorin, Ilorin, Nigeria
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Takano T, Wakayama Y, Doki T. Endocytic Pathway of Feline Coronavirus for Cell Entry: Differences in Serotype-Dependent Viral Entry Pathway. Pathogens 2019; 8:pathogens8040300. [PMID: 31888266 PMCID: PMC6963708 DOI: 10.3390/pathogens8040300] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Revised: 12/15/2019] [Accepted: 12/15/2019] [Indexed: 12/30/2022] Open
Abstract
Feline coronavirus (FCoV) is a pathogen causing a lethal infectious disease in cats, feline infectious peritonitis. It has two serotypes (type I FCoV and type II FCoV). According to our previous study, type I FCoV infection is inhibited by compounds inducing intracellular cholesterol accumulation, whereas type II FCoV infection is not inhibited. Intracellular cholesterol accumulation was reported to disrupt late endosome function. Based on these findings, types I and II FCoV are considered to enter the cytosol through late and early endosomes, respectively. We investigated whether the antiviral activities of a late endosome trafficking inhibitor and cholesterol-accumulating agents are different between the FCoV serotypes. The late endosome trafficking inhibitor did not inhibit type II FCoV infection, but it inhibited type I FCoV infection. Type I FCoV infection was inhibited by cholesterol-accumulating triazoles, but not by non-cholesterol-accumulating triazoles. These phenomena were observed in both feline cell lines and feline primary macrophages. This study provides additional information on the differences in intracellular reproductive cycle between type I and type II FCoV.
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Han Z, Liwen X, Ren M, Sheng J, Ma T, Sun J, Zhao Y, Liu S. Genetic, antigenic and pathogenic characterization of avian coronaviruses isolated from pheasants (Phasianus colchicus) in China. Vet Microbiol 2019; 240:108513. [PMID: 31902509 PMCID: PMC7117390 DOI: 10.1016/j.vetmic.2019.108513] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2019] [Revised: 11/15/2019] [Accepted: 11/19/2019] [Indexed: 02/07/2023]
Abstract
Two pheasant coronaviruses (PhCoVs) were isolated in 2017 in China. The two PhCoVs were genetically similar to IBV. Pathogenicity, replication, and shedding of PhCoV were obvious different when infected chickens and pheasants. PhCoVs isolated from different outbreaks may have evolved independently from IBVs by adaption in pheasants.
Two viruses were isolated in 2017 from commercial pheasants with severe clinical signs and mortality in Shandong and Anhui provinces, China, respectively. We examined the pathogenic effects of the viruses in chicken embryos and the size and morphology of the virus particles, performed phylogenetic analysis based on the S1 gene and complete genomic sequences, and examined the antibody responses against infectious bronchitis virus (IBV). The results suggested that the viruses I0623/17 and I0710/17 were avian coronaviruses and were identified as pheasant coronaviruses (PhCoV), with greatest similarity to IBV. Further investigations of the antigenicity, complete genome organization, substitutions in multiple genes, and viral pathogenicity, replication, and shedding in chickens and pheasants showed obvious differences between PhCoV and IBV in terms of antigenicity, and viral pathogenicity, replication, and shedding in chickens and pheasants. The close genetic relationship, but obvious differences between PhCoVs and IBVs suggested the IBVs could be the ancestors of PhCoVs, and that PhCoVs isolated from different outbreaks may have evolved independently from IBVs circulating in the specific region by adaption in pheasants. This hypothesis was supported by analysis of the S1 gene fragments of the two PhCoVs isolated in the current study, as well as PhCoVs isolated in the UK and selected IBV strains. Such analyses indicated different evolution patterns and different tissue tropisms between PhCoVs isolated in different outbreaks. Further studies are needed to confirm this hypothesis by studying the complete genomic sequences of PhCoVs from different outbreaks and the pathogenicity of IBVs in pheasants to compare and clarify the relationships between PhCoVs and IBVs.
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Affiliation(s)
- Zongxi Han
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
| | - Xu Liwen
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
| | - Mengting Ren
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
| | - Jie Sheng
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
| | - Tianxin Ma
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
| | - Junfeng Sun
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
| | - Yan Zhao
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
| | - Shengwang Liu
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, the Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China.
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Biochemical Analysis of Coronavirus Spike Glycoprotein Conformational Intermediates during Membrane Fusion. J Virol 2019; 93:JVI.00785-19. [PMID: 31315988 PMCID: PMC6744234 DOI: 10.1128/jvi.00785-19] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 07/05/2019] [Indexed: 11/20/2022] Open
Abstract
A fusion protein expressed on the surface of enveloped viruses mediates fusion of the viral and cellular membranes to facilitate virus infection. Pre- and postfusion structures of viral fusion proteins have been characterized, but conformational changes between them remain poorly understood. Here, we examined the intermediate conformation of the murine coronavirus fusion protein, called the spike protein, which must be cleaved by a cellular protease following receptor binding. Western blot analysis of protease digestion products revealed that two subunits (67 and 69 kDa) are produced from a single spike protein (180 kDa). These two subunits were considered to be by-products derived from conformational changes and were useful for probing the intermediate conformation of the spike protein. Interaction with a heptad repeat (HR) peptide revealed that these subunits adopt packed and unpacked conformations, respectively, and two-dimensional electrophoresis revealed a trimeric assembly. Based on biochemical observations, we propose an asymmetric trimer model for the intermediate structure of the spike protein. Receptor binding induces the membrane-binding potential of the trimer, in which at least one HR motif forms a packed-hairpin structure, while membrane fusion subunits are covered by the receptor-binding subunit, thereby preventing the spike protein from forming the typical homotrimeric prehairpin structure predicted by the current model of class I viral fusion protein. Subsequent proteolysis induces simultaneous packing of the remaining unpacked HRs upon assembly of three HRs at the central axis to generate a six-helix bundle. Our model proposes a key mechanism for membrane fusion of enveloped viruses.IMPORTANCE Recent studies using single-particle cryo-electron microscopy (cryoEM) revealed the mechanism underlying activation of viral fusion protein at the priming stage. However, characterizing the subsequent triggering stage underpinning transition from pre- to postfusion structures is difficult because single-particle cryoEM excludes unstable structures that appear as heterogeneous shapes. Therefore, population-based biochemical analysis is needed to capture features of unstable proteins. Here, we analyzed protease digestion products of a coronavirus fusion protein during activation; their sizes appear to be affected directly by the conformational state. We propose a model for the viral fusion protein in the intermediate state, which involves a compact structure and conformational changes that overcome steric hindrance within the three fusion protein subunits.
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Braun E, Sauter D. Furin-mediated protein processing in infectious diseases and cancer. Clin Transl Immunology 2019; 8:e1073. [PMID: 31406574 PMCID: PMC6682551 DOI: 10.1002/cti2.1073] [Citation(s) in RCA: 195] [Impact Index Per Article: 39.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 07/10/2019] [Accepted: 07/13/2019] [Indexed: 12/17/2022] Open
Abstract
Proteolytic cleavage regulates numerous processes in health and disease. One key player is the ubiquitously expressed serine protease furin, which cleaves a plethora of proteins at polybasic recognition motifs. Mammalian substrates of furin include cytokines, hormones, growth factors and receptors. Thus, it is not surprising that aberrant furin activity is associated with a variety of disorders including cancer. Furthermore, the enzymatic activity of furin is exploited by numerous viral and bacterial pathogens, thereby enhancing their virulence and spread. In this review, we describe the physiological and pathophysiological substrates of furin and discuss how dysregulation of a simple proteolytic cleavage event may promote infectious diseases and cancer. One major focus is the role of furin in viral glycoprotein maturation and pathogenicity. We also outline cellular mechanisms regulating the expression and activation of furin and summarise current approaches that target this protease for therapeutic intervention.
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Affiliation(s)
- Elisabeth Braun
- Institute of Molecular VirologyUlm University Medical CenterUlmGermany
| | - Daniel Sauter
- Institute of Molecular VirologyUlm University Medical CenterUlmGermany
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Zhang J, Chen J, Shi D, Shi H, Zhang X, Liu J, Cao L, Zhu X, Liu Y, Wang X, Ji Z, Feng L. Porcine deltacoronavirus enters cells via two pathways: A protease-mediated one at the cell surface and another facilitated by cathepsins in the endosome. J Biol Chem 2019; 294:9830-9843. [PMID: 31068417 PMCID: PMC6597833 DOI: 10.1074/jbc.ra119.007779] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 05/02/2019] [Indexed: 11/06/2022] Open
Abstract
Porcine deltacoronavirus (PDCoV) is a pathogen belonging to the genus Deltacoronavirus that in 2014 caused outbreaks of piglet diarrhea in the United States. To identify suitable therapeutic targets, a more comprehensive understanding of the viral entry pathway is required, particularly of the role of proteases. Here, we identified the proteases that activate the viral spike (S) glycoprotein to initiate cell entry and also pinpointed the host-cellular pathways that PDCoV uses for entry. Our results revealed that cathepsin L (CTSL) and cathepsin B (CTSB) in lysosomes and extracellular trypsin in cell cultures independently activate the S protein for membrane fusion. Pretreating the cells with the lysosomal acidification inhibitor bafilomycin-A1 (Baf-A1) completely inhibited PDCoV entry, and siRNA-mediated ablation of CTSL or CTSB expression significantly reduced viral infection, indicating that PDCoV uses an endosomal pathway for entry. Of note, trypsin treatment of cell cultures also activated PDCoV entry, even when the endosomal pathway was inhibited. This observation indicated that trypsin-induced S protein cleavage and activation in cell cultures enables viral entry directly from the cell surface. Our results provide critical insights into the PDCoV infection mechanism, uncovering two distinct viral entry pathways: one through cathepsin L and cathepsin B in the endosome and another via a protease at the cell surface. Because PDCoV infection sites represent a proteases-rich environment, these findings suggest that endosome inhibitor treatment alone is insufficient to block PDCoV entry into intestinal epithelial cells in vivo Therefore, approaches that inhibit viral entry from the cell membrane should also be considered.
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Affiliation(s)
- Jialin Zhang
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Jianfei Chen
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Da Shi
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Hongyan Shi
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Xin Zhang
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Jianbo Liu
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Liyan Cao
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Xiangdong Zhu
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Ye Liu
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Xiaobo Wang
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Zhaoyang Ji
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
| | - Li Feng
- From the State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China
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J Alsaadi EA, Jones IM. Membrane binding proteins of coronaviruses. Future Virol 2019; 14:275-286. [PMID: 32201500 PMCID: PMC7079996 DOI: 10.2217/fvl-2018-0144] [Citation(s) in RCA: 133] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 02/19/2019] [Indexed: 12/12/2022]
Abstract
Coronaviruses (CoVs) infect many species causing a variety of diseases with a range of severities. Their members include zoonotic viruses with pandemic potential where therapeutic options are currently limited. Despite this diversity CoVs share some common features including the production, in infected cells, of elaborate membrane structures. Membranes represent both an obstacle and aid to CoV replication - and in consequence - virus-encoded structural and nonstructural proteins have membrane-binding properties. The structural proteins encounter cellular membranes at both entry and exit of the virus while the nonstructural proteins reorganize cellular membranes to benefit virus replication. Here, the role of each protein in membrane binding is described to provide a comprehensive picture of their role in the CoV replication cycle.
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Affiliation(s)
- Entedar A J Alsaadi
- Biomedical Sciences, School of Biological Sciences, University of Reading, Reading RG6 6AJ, UK.,Department of Microbiology, College of Medicine, Thiqar University, Thiqar, Iraq.,Biomedical Sciences, School of Biological Sciences, University of Reading, Reading RG6 6AJ, UK.,Department of Microbiology, College of Medicine, Thiqar University, Thiqar, Iraq
| | - Ian M Jones
- Biomedical Sciences, School of Biological Sciences, University of Reading, Reading RG6 6AJ, UK.,Biomedical Sciences, School of Biological Sciences, University of Reading, Reading RG6 6AJ, UK
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Tetraspanins: Architects of Viral Entry and Exit Platforms. J Virol 2019; 93:JVI.01429-17. [PMID: 30567993 PMCID: PMC6401424 DOI: 10.1128/jvi.01429-17] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 12/11/2018] [Indexed: 01/09/2023] Open
Abstract
Host factors render cells susceptible to viral infection. One family of susceptibility factors, the tetraspanin proteins, facilitate enveloped virus entry by promoting virus-cell membrane fusion. Host factors render cells susceptible to viral infection. One family of susceptibility factors, the tetraspanin proteins, facilitate enveloped virus entry by promoting virus-cell membrane fusion. They also facilitate viral egress from infected cells. In this Gem, we discuss recent insights into how tetraspanins assemble viral entry and exit platforms on cell membranes, and we speculate that tetraspanins contribute to nonviral membrane fusions by similar mechanisms.
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Bickerton E, Maier HJ, Stevenson-Leggett P, Armesto M, Britton P. The S2 Subunit of Infectious Bronchitis Virus Beaudette Is a Determinant of Cellular Tropism. J Virol 2018; 92:e01044-18. [PMID: 30021894 PMCID: PMC6146808 DOI: 10.1128/jvi.01044-18] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 07/10/2018] [Indexed: 12/17/2022] Open
Abstract
The spike (S) glycoprotein of the avian gammacoronavirus infectious bronchitis virus (IBV) is comprised of two subunits (S1 and S2), has a role in virulence in vivo, and is responsible for cellular tropism in vitro We have previously demonstrated that replacement of the S glycoprotein ectodomain from the avirulent Beaudette strain of IBV with the corresponding region from the virulent M41-CK strain resulted in a recombinant virus, BeauR-M41(S), with the in vitro cell tropism of M41-CK. The IBV Beaudette strain is able to replicate in both primary chick kidney cells and Vero cells, whereas the IBV M41-CK strain replicates in primary cells only. In order to investigate the region of the IBV S responsible for growth in Vero cells, we generated a series of recombinant IBVs expressing chimeric S glycoproteins, consisting of regions from the Beaudette and M41-CK S gene sequences, within the genomic background of Beaudette. The S2, but not the S1, subunit of the Beaudette S was found to confer the ability to grow in Vero cells. Various combinations of Beaudette-specific amino acids were introduced into the S2 subunit of M41 to determine the minimum requirement to confer tropism for growth in Vero cells. The ability of IBV to grow and produce infectious progeny virus in Vero cells was subsequently narrowed down to just 3 amino acids surrounding the S2' cleavage site. Conversely, swapping of the 3 Beaudette-associated amino acids with the corresponding ones from M41 was sufficient to abolish Beaudette growth in Vero cells.IMPORTANCE Infectious bronchitis remains a major problem in the global poultry industry, despite the existence of many different vaccines. IBV vaccines, both live attenuated and inactivated, are currently grown on embryonated hen's eggs, a cumbersome and expensive process due to the fact that most IBV strains do not grow in cultured cells. The reverse genetics system for IBV creates the opportunity for generating rationally designed and more effective vaccines. The observation that IBV Beaudette has the additional tropism for growth on Vero cells also invokes the possibility of generating IBV vaccines produced from cultured cells rather than by the use of embryonated eggs. The regions of the IBV Beaudette S glycoprotein involved in the determination of extended cellular tropism were identified in this study. This information will enable the rational design of a future generation of IBV vaccines that may be grown on Vero cells.
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Middle East Respiratory Syndrome Coronavirus Spike Protein Is Not Activated Directly by Cellular Furin during Viral Entry into Target Cells. J Virol 2018; 92:JVI.00683-18. [PMID: 30021905 DOI: 10.1128/jvi.00683-18] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 07/09/2018] [Indexed: 12/19/2022] Open
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) utilizes host cellular proteases to enter cells. A previous report shows that furin, which is distributed mainly in the Golgi apparatus and cycled to the cell surface and endosomes, proteolytically activates the MERS-CoV spike (S) protein following receptor binding to mediate fusion between the viral and cellular membranes. In this study, we reexamined furin usage by MERS-CoV using a real-time PCR-based virus cell entry assay after inhibition of cellular proteases. We found that the furin inhibitor dec-RVKR-CMK blocked entry of MERS-CoV harboring an S protein lacking furin cleavage sites; it even blocked entry into furin-deficient LoVo cells. In addition, dec-RVKR-CMK inhibited not only the enzymatic activity of furin but also those of cathepsin L, cathepsin B, trypsin, papain, and TMPRSS2. Furthermore, a virus cell entry assay and a cell-cell fusion assay provided no evidence that the S protein was activated by exogenous furin. Therefore, we conclude that furin does not play a role in entry of MERS-CoV into cells and that the inhibitory effect of dec-RVKR-CMK is specific for TMPRSS2 and cathepsin L rather than furin.IMPORTANCE Previous studies using the furin inhibitor dec-RVKR-CMK suggest that MERS-CoV utilizes a cellular protease, furin, to activate viral glycoproteins during cell entry. However, we found that dec-RVKR-CMK inhibits not only furin but also other proteases. Furthermore, we found no evidence that MERS-CoV uses furin. These findings suggest that previous studies in the virology field based on dec-RVKR-CMK should be reexamined carefully. Here we describe appropriate experiments that can be used to assess the effect of protease inhibitors on virus cell entry.
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Identification of H209 as Essential for pH 8-Triggered Receptor-Independent Syncytium Formation by S Protein of Mouse Hepatitis Virus A59. J Virol 2018. [PMID: 29514915 DOI: 10.1128/jvi.00209-18] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The spike glycoprotein (S) of murine coronavirus mouse hepatitis virus (MHV) strain A59 uses murine carcinoembryonic antigen-related cell adhesion molecule 1a as its receptor for cell entry, but S protein can also be triggered in the absence of receptor by pH 8.0 alone at 37°C. The mechanism by which conformational changes of this S glycoprotein can be triggered by pH 8.0 has not yet been determined. Here, we show that MHV-A59 S protein is triggered by pH 8.0 at 37°C to induce receptor-independent syncytium (RIS) formation on 293T cells, and that the conformational changes in S proteins triggered by pH 8.0 are very similar to those triggered by receptor binding. We systemically mutated each of 15 histidine residues in S protein and found that H209 is essential for pH 8.0-triggered RIS formation, while H179, H441, H643, and H759 also play important roles in this process. Replacement of H209 with Ala had no effect on receptor binding, but in murine 17Cl.1 cells mutant H209A MHV-A59 showed delayed growth kinetics and was readily outcompeted by wild-type virus when mixed together, indicating that the H209A mutation caused a defect in virus fitness. Finally, the H209A mutation significantly increased the thermostability of S protein in its prefusion conformation, which may raise the energy barrier for conformational change of S protein required for membrane fusion and lead to a decrease in virus fitness in cell culture. Thus, MHV-A59 may have evolved to lower the stability of its S protein in order to increase virus fitness.IMPORTANCE Enveloped viruses enter cells through fusion of viral and cellular membranes, and the process is mediated by interactions between viral envelope proteins and their host receptors. In the prefusion conformation, viral envelope proteins are metastable, and activation to the fusion conformation is tightly regulated, since premature activation would lead to loss of viral infectivity. The stability of viral envelope proteins greatly influences their activation and virus fitness. Here, we report that, similar to the A82V mutation in Ebola glycoprotein, in the S glycoprotein of murine coronavirus MHV-A59, the histidine residue at position of 209 significantly affects the thermal stability of the S protein, determines whether S protein can be activated at 37°C by either pH 8.0 alone or by receptor binding, and affects viral fitness in cell culture. Thus, the spike glycoprotein of MHV-A59 has evolved to retain histidine at position 209 to optimize virus fitness.
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Böttcher-Friebertshäuser E, Garten W, Klenk HD. Characterization of Proprotein Convertases and Their Involvement in Virus Propagation. ACTIVATION OF VIRUSES BY HOST PROTEASES 2018. [PMCID: PMC7122180 DOI: 10.1007/978-3-319-75474-1_9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
| | - Wolfgang Garten
- Institut für Virologie, Philipps Universität, Marburg, Germany
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Böttcher-Friebertshäuser E, Garten W, Klenk HD. Priming Time: How Cellular Proteases Arm Coronavirus Spike Proteins. ACTIVATION OF VIRUSES BY HOST PROTEASES 2018. [PMCID: PMC7122371 DOI: 10.1007/978-3-319-75474-1_4] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Coronaviruses are enveloped RNA viruses that infect mammals and birds. Infection of humans with globally circulating human coronaviruses is associated with the common cold. In contrast, transmission of animal coronaviruses to humans can result in severe disease: The severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS) are responsible for hundreds of deaths in Asia and the Middle East, respectively, and are both caused by members of the genus Betacoronavirus, SARS-CoV, and MERS-CoV that were zoonotically transmitted from an animal host to humans. At present, neither vaccines nor specific treatment is available to combat coronavirus infection in humans, and novel antiviral strategies are urgently sought. The viral spike protein (S) mediates the first essential step in coronavirus infection, viral entry into target cells. For this, the S protein critically depends on priming by host cell proteases, and the responsible enzymes are potential targets for antiviral intervention. Recent studies revealed that the endosomal cysteine protease cathepsin L and the serine proteases furin and TMPRSS2 prime the S proteins of SARS-CoV and MERS-CoV and provided evidence that successive S protein cleavage at two sites is required for S protein priming. Moreover, mechanisms that control protease choice were unraveled, and insights were obtained into which enzyme promotes viral spread in the host. Here, we will provide basic information on S protein function and proteolytic priming, and we will then discuss recent progress in our understanding of the priming of the S proteins of SARS-CoV and MERS-CoV.
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Affiliation(s)
| | - Wolfgang Garten
- Institut für Virologie, Philipps Universität, Marburg, Germany
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Neurovirulent Murine Coronavirus JHM.SD Uses Cellular Zinc Metalloproteases for Virus Entry and Cell-Cell Fusion. J Virol 2017; 91:JVI.01564-16. [PMID: 28148786 DOI: 10.1128/jvi.01564-16] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 01/24/2017] [Indexed: 12/27/2022] Open
Abstract
The coronavirus (CoV) S protein requires cleavage by host cell proteases to mediate virus-cell and cell-cell fusion. Many strains of the murine coronavirus mouse hepatitis virus (MHV) have distinct, S-dependent organ and tissue tropisms despite using a common receptor, suggesting that they employ different cellular proteases for fusion. In support of this hypothesis, we found that inhibition of endosomal acidification only modestly decreased entry, and overexpression of the cell surface protease TMPRSS2 greatly enhanced entry, of the highly neurovirulent MHV strain JHM.SD relative to their effects on the reference strain, A59. However, TMPRSS2 overexpression decreased MHV structural protein expression, release of infectious particles, and syncytium formation, and endogenous serine protease activity did not contribute greatly to infection. We therefore investigated the importance of other classes of cellular proteases and found that inhibition of matrix metalloproteinase (MMP)- and a disintegrin and metalloprotease (ADAM)-family zinc metalloproteases markedly decreased both entry and cell-cell fusion. Suppression of virus by metalloprotease inhibition varied among tested cell lines and MHV S proteins, suggesting a role for metalloprotease use in strain-dependent tropism. We conclude that zinc metalloproteases must be considered potential contributors to coronavirus fusion.IMPORTANCE The family Coronaviridae includes viruses that cause two emerging diseases of humans, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), as well as a number of important animal pathogens. Because coronaviruses depend on host protease-mediated cleavage of their S proteins for entry, a number of protease inhibitors have been proposed as antiviral agents. However, it is unclear which proteases mediate in vivo infection. For example, SARS-CoV infection of cultured cells depends on endosomal acid pH-dependent proteases rather than on the cell surface acid pH-independent serine protease TMPRSS2, but Zhou et al. (Antiviral Res 116:76-84, 2015, doi:10.1016/j.antiviral.2015.01.011) found that a serine protease inhibitor was more protective than a cathepsin inhibitor in SARS-CoV-infected mice. This paper explores the contributions of endosomal acidification and various proteases to coronavirus infection and identifies an unexpected class of proteases, the matrix metalloproteinase and ADAM families, as potential targets for anticoronavirus therapy.
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Proteolytic processing of Middle East respiratory syndrome coronavirus spikes expands virus tropism. Proc Natl Acad Sci U S A 2016; 113:12262-12267. [PMID: 27791014 DOI: 10.1073/pnas.1608147113] [Citation(s) in RCA: 228] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) infects humans from zoonotic sources and causes severe pulmonary disease. Virions require spike (S) glycoproteins for binding to cell receptors and for catalyzing virus-cell membrane fusion. Fusion occurs only after S proteins are cleaved sequentially, first during their secretion through the exocytic organelles of virus-producing cells, and second after virus binding to target-cell receptors. To more precisely determine how sequential proteolysis contributes to CoV infection, we introduced S mutations obstructing the first cleavages. These mutations severely compromised MERS-CoV infection into human lung-derived cells, but had little effect on infection into several other cell types. These cell type-specific requirements for proteolysis correlated with S conformations during cell entry. Without the first cleavages, S proteins resisted cell receptor-induced conformational changes, which restricted the second, fusion-activating cleavages. Consistent with these findings, precleaved MERS viruses used receptor-proximal, cell-surface proteases to effect the second fusion-activating cleavages during cell entry, whereas the more rigid uncleaved MERS viruses trafficked past these cell-surface proteases and into endosomes. Uncleaved viruses were less infectious to human airway epithelial and Calu3 cell cultures because they lacked sufficient endosomal fusion-activating proteases. Thus, by sensitizing viruses to receptor-induced conformational changes, the first S cleavages expand virus tropism to cell types that are relevant to lung infection, and therefore may be significant determinants of MERS-CoV virulence.
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White JM, Whittaker GR. Fusion of Enveloped Viruses in Endosomes. Traffic 2016; 17:593-614. [PMID: 26935856 PMCID: PMC4866878 DOI: 10.1111/tra.12389] [Citation(s) in RCA: 281] [Impact Index Per Article: 35.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Revised: 02/25/2016] [Accepted: 02/25/2016] [Indexed: 12/12/2022]
Abstract
Ari Helenius launched the field of enveloped virus fusion in endosomes with a seminal paper in the Journal of Cell Biology in 1980. In the intervening years, a great deal has been learned about the structures and mechanisms of viral membrane fusion proteins as well as about the endosomes in which different enveloped viruses fuse and the endosomal cues that trigger fusion. We now recognize three classes of viral membrane fusion proteins based on structural criteria and four mechanisms of fusion triggering. After reviewing general features of viral membrane fusion proteins and viral fusion in endosomes, we delve into three characterized mechanisms for viral fusion triggering in endosomes: by low pH, by receptor binding plus low pH and by receptor binding plus the action of a protease. We end with a discussion of viruses that may employ novel endosomal fusion‐triggering mechanisms. A key take‐home message is that enveloped viruses that enter cells by fusing in endosomes traverse the endocytic pathway until they reach an endosome that has all of the environmental conditions (pH, proteases, ions, intracellular receptors and lipid composition) to (if needed) prime and (in all cases) trigger the fusion protein and to support membrane fusion.
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Affiliation(s)
- Judith M White
- Department of Cell Biology, University of Virginia, Charlottesville, VA, USA
| | - Gary R Whittaker
- Department of Microbiology & Immunology, Cornell University, Ithaca, NY, USA
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Le Coupanec A, Desforges M, Meessen-Pinard M, Dubé M, Day R, Seidah NG, Talbot PJ. Cleavage of a Neuroinvasive Human Respiratory Virus Spike Glycoprotein by Proprotein Convertases Modulates Neurovirulence and Virus Spread within the Central Nervous System. PLoS Pathog 2015; 11:e1005261. [PMID: 26545254 PMCID: PMC4636366 DOI: 10.1371/journal.ppat.1005261] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Accepted: 10/16/2015] [Indexed: 11/24/2022] Open
Abstract
Human coronaviruses (HCoV) are respiratory pathogens that may be associated with the development of neurological diseases, in view of their neuroinvasive and neurotropic properties. The viral spike (S) glycoprotein is a major virulence factor for several coronavirus species, including the OC43 strain of HCoV (HCoV-OC43). In an attempt to study the role of this protein in virus spread within the central nervous system (CNS) and neurovirulence, as well as to identify amino acid residues important for such functions, we compared the sequence of the S gene found in the laboratory reference strain HCoV-OC43 ATCC VR-759 to S sequences of viruses detected in clinical isolates from the human respiratory tract. We identified one predominant mutation at amino acid 758 (from RRSR↓ G758 to RRSR↓R758), which introduces a putative furin-like cleavage (↓) site. Using a molecular cDNA infectious clone to generate a corresponding recombinant virus, we show for the first time that such point mutation in the HCoV-OC43 S glycoprotein creates a functional cleavage site between the S1 and S2 portions of the S protein. While the corresponding recombinant virus retained its neuroinvasive properties, this mutation led to decreased neurovirulence while potentially modifying the mode of virus spread, likely leading to a limited dissemination within the CNS. Taken together, these results are consistent with the adaptation of HCoV-OC43 to the CNS environment, resulting from the selection of quasi-species harboring mutations that lead to amino acid changes in viral genes, like the S gene in HCoV-OC43, which may contribute to a more efficient establishment of a less pathogenic but persistent CNS infection. This adaptative mechanism could potentially be associated with human encephalitis or other neurological degenerative pathologies. Human coronaviruses (HCoV) are respiratory pathogens involved in a sizable proportion of common colds. They have over the years been associated with the development of neurological diseases, given their demonstrated neuroinvasive and neurotropic properties. The viral spike (S) glycoprotein appears to be associated with these neurologic features and is a major factor of virulence for several coronavirus species, including HCoV-OC43. To further characterize the role of this protein in neurovirulence and virus spread within the CNS, we sought to identify amino acid residues that may be important for this function. Our data revealed that one of them, G758R, introduces a functional furin-like cleavage site in the S protein (RRSR↓R758). This change in S protein mostly impacts neurovirulence, which seems associated with a modified viral dissemination, without significantly affecting its neuroinvasive capacity. This mutation, found in all characterized contemporary human clinical respiratory isolates, underlines previous findings that naturally existing field isolates of HCoV-OC43 variants still possess the capacity to invade the CNS where they could eventually adapt and establish a persistent human CNS infection, a mechanism potentially associated with human encephalitis or neurodegenerative pathologies of unknown etiologies.
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Affiliation(s)
- Alain Le Coupanec
- Laboratory of Neuroimmunovirology, INRS-Institut Armand-Frappier, Université du Québec, Laval, Québec, Canada
| | - Marc Desforges
- Laboratory of Neuroimmunovirology, INRS-Institut Armand-Frappier, Université du Québec, Laval, Québec, Canada
- * E-mail: (MDe); (PJT)
| | - Mathieu Meessen-Pinard
- Laboratory of Neuroimmunovirology, INRS-Institut Armand-Frappier, Université du Québec, Laval, Québec, Canada
| | - Mathieu Dubé
- Laboratory of Neuroimmunovirology, INRS-Institut Armand-Frappier, Université du Québec, Laval, Québec, Canada
| | - Robert Day
- Institut de Pharmacologie de Sherbrooke, Faculté de Médecine et Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Nabil G. Seidah
- Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, Montréal, Québec, Canada
| | - Pierre J. Talbot
- Laboratory of Neuroimmunovirology, INRS-Institut Armand-Frappier, Université du Québec, Laval, Québec, Canada
- * E-mail: (MDe); (PJT)
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Abolnik C. Genomic and single nucleotide polymorphism analysis of infectious bronchitis coronavirus. INFECTION, GENETICS AND EVOLUTION : JOURNAL OF MOLECULAR EPIDEMIOLOGY AND EVOLUTIONARY GENETICS IN INFECTIOUS DISEASES 2015; 32:416-24. [PMID: 25843648 PMCID: PMC7106318 DOI: 10.1016/j.meegid.2015.03.033] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/05/2014] [Revised: 03/13/2015] [Accepted: 03/26/2015] [Indexed: 01/03/2023]
Abstract
Infectious bronchitis virus (IBV) is a Gammacoronavirus that causes a highly contagious respiratory disease in chickens. A QX-like strain was analysed by high-throughput Illumina sequencing and genetic variation across the entire viral genome was explored at the sub-consensus level by single nucleotide polymorphism (SNP) analysis. Thirteen open reading frames (ORFs) in the order 5'-UTR-1a-1ab-S-3a-3b-E-M-4b-4c-5a-5b-N-6b-3'UTR were predicted. The relative frequencies of missense: silent SNPs were calculated to obtain a comparative measure of variability in specific genes. The most variable ORFs in descending order were E, 3b, 5'UTR, N, 1a, S, 1ab, M, 4c, 5a, 6b. The E and 3b protein products play key roles in coronavirus virulence, and RNA folding demonstrated that the mutations in the 5'UTR did not alter the predicted secondary structure. The frequency of SNPs in the Spike (S) protein ORF of 0.67% was below the genomic average of 0.76%. Only three SNPS were identified in the S1 subunit, none of which were located in hypervariable region (HVR) 1 or HVR2. The S2 subunit was considerably more variable containing 87% of the polymorphisms detected across the entire S protein. The S2 subunit also contained a previously unreported multi-A insertion site and a stretch of four consecutive mutated amino acids, which mapped to the stalk region of the spike protein. Template-based protein structure modelling produced the first theoretical model of the IBV spike monomer. Given the lack of diversity observed at the sub-consensus level, the tenet that the HVRs in the S1 subunit are very tolerant of amino acid changes produced by genetic drift is questioned.
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Affiliation(s)
- Celia Abolnik
- Poultry Section, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort 0110, South Africa.
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Lewis CS, Porter E, Matthews D, Kipar A, Tasker S, Helps CR, Siddell SG. Genotyping coronaviruses associated with feline infectious peritonitis. J Gen Virol 2015; 96:1358-1368. [PMID: 25667330 PMCID: PMC4635486 DOI: 10.1099/vir.0.000084] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Accepted: 02/03/2015] [Indexed: 12/21/2022] Open
Abstract
Feline coronavirus (FCoV) infections are endemic among cats worldwide. The majority of infections are asymptomatic or result in only mild enteric disease. However, approximately 5 % of cases develop feline infectious peritonitis (FIP), a systemic disease that is a frequent cause of death in young cats. In this study, we report the complete coding genome sequences of six FCoVs: three from faecal samples from healthy cats and three from tissue lesion samples from cats with confirmed FIP. The six samples were obtained over a period of 8 weeks at a single-site cat rescue and rehoming centre in the UK. We found amino acid differences located at 44 positions across an alignment of the six virus translatomes and, at 21 of these positions, the differences fully or partially discriminated between the genomes derived from the faecal samples and the genomes derived from the tissue lesion samples. In this study, two amino acid differences fully discriminated the two classes of genomes: these were both located in the S2 domain of the virus surface glycoprotein gene. We also identified deletions in the 3c protein ORF of genomes from two of the FIP samples. Our results support previous studies that implicate S protein mutations in the pathogenesis of FIP.
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Affiliation(s)
- Catherine S Lewis
- School of Cellular and Molecular Medicine, University of Bristol, Bristol BS8 1TD, UK
| | - Emily Porter
- School of Veterinary Sciences, University of Bristol, Langford, Bristol BS40 5DU, UK
| | - David Matthews
- School of Cellular and Molecular Medicine, University of Bristol, Bristol BS8 1TD, UK
| | - Anja Kipar
- Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Winterthurer Strasse 268, 8057 Zurich, Switzerland
| | - Séverine Tasker
- School of Veterinary Sciences, University of Bristol, Langford, Bristol BS40 5DU, UK
| | - Christopher R Helps
- School of Veterinary Sciences, University of Bristol, Langford, Bristol BS40 5DU, UK
| | - Stuart G Siddell
- School of Cellular and Molecular Medicine, University of Bristol, Bristol BS8 1TD, UK
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Host cell proteases: Critical determinants of coronavirus tropism and pathogenesis. Virus Res 2014; 202:120-34. [PMID: 25445340 PMCID: PMC4465284 DOI: 10.1016/j.virusres.2014.11.021] [Citation(s) in RCA: 611] [Impact Index Per Article: 61.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 11/08/2014] [Accepted: 11/13/2014] [Indexed: 11/25/2022]
Abstract
Coronavirus spike proteins can be cleaved by a multitude of host cell proteases. Proteolytic activation of spike is a crucial step to activate its fusogenicity. The spike protein can be cleaved at multiple sites. Modulation of spike cleavage can have profound effects on tropism and pathogenesis.
Coronaviruses are a large group of enveloped, single-stranded positive-sense RNA viruses that infect a wide range of avian and mammalian species, including humans. The emergence of deadly human coronaviruses, severe acute respiratory syndrome coronavirus (SARS-CoV), and Middle East respiratory syndrome coronavirus (MERS-CoV) have bolstered research in these viral and often zoonotic pathogens. While coronavirus cell and tissue tropism, host range, and pathogenesis are initially controlled by interactions between the spike envelope glycoprotein and host cell receptor, it is becoming increasingly apparent that proteolytic activation of spike by host cell proteases also plays a critical role. Coronavirus spike proteins are the main determinant of entry as they possess both receptor binding and fusion functions. Whereas binding to the host cell receptor is an essential first step in establishing infection, the proteolytic activation step is often critical for the fusion function of spike, as it allows for controlled release of the fusion peptide into target cellular membranes. Coronaviruses have evolved multiple strategies for proteolytic activation of spike, and a large number of host proteases have been shown to proteolytically process the spike protein. These include, but are not limited to, endosomal cathepsins, cell surface transmembrane protease/serine (TMPRSS) proteases, furin, and trypsin. This review focuses on the diversity of strategies coronaviruses have evolved to proteolytically activate their fusion protein during spike protein biosynthesis and the critical entry step of their life cycle, and highlights important findings on how proteolytic activation of coronavirus spike influences tissue and cell tropism, host range and pathogenicity.
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Burkard C, Verheije MH, Wicht O, van Kasteren SI, van Kuppeveld FJ, Haagmans BL, Pelkmans L, Rottier PJM, Bosch BJ, de Haan CAM. Coronavirus cell entry occurs through the endo-/lysosomal pathway in a proteolysis-dependent manner. PLoS Pathog 2014; 10:e1004502. [PMID: 25375324 PMCID: PMC4223067 DOI: 10.1371/journal.ppat.1004502] [Citation(s) in RCA: 280] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Accepted: 10/02/2014] [Indexed: 02/07/2023] Open
Abstract
Enveloped viruses need to fuse with a host cell membrane in order to deliver their genome into the host cell. While some viruses fuse with the plasma membrane, many viruses are endocytosed prior to fusion. Specific cues in the endosomal microenvironment induce conformational changes in the viral fusion proteins leading to viral and host membrane fusion. In the present study we investigated the entry of coronaviruses (CoVs). Using siRNA gene silencing, we found that proteins known to be important for late endosomal maturation and endosome-lysosome fusion profoundly promote infection of cells with mouse hepatitis coronavirus (MHV). Using recombinant MHVs expressing reporter genes as well as a novel, replication-independent fusion assay we confirmed the importance of clathrin-mediated endocytosis and demonstrated that trafficking of MHV to lysosomes is required for fusion and productive entry to occur. Nevertheless, MHV was shown to be less sensitive to perturbation of endosomal pH than vesicular stomatitis virus and influenza A virus, which fuse in early and late endosomes, respectively. Our results indicate that entry of MHV depends on proteolytic processing of its fusion protein S by lysosomal proteases. Fusion of MHV was severely inhibited by a pan-lysosomal protease inhibitor, while trafficking of MHV to lysosomes and processing by lysosomal proteases was no longer required when a furin cleavage site was introduced in the S protein immediately upstream of the fusion peptide. Also entry of feline CoV was shown to depend on trafficking to lysosomes and processing by lysosomal proteases. In contrast, MERS-CoV, which contains a minimal furin cleavage site just upstream of the fusion peptide, was negatively affected by inhibition of furin, but not of lysosomal proteases. We conclude that a proteolytic cleavage site in the CoV S protein directly upstream of the fusion peptide is an essential determinant of the intracellular site of fusion. Enveloped viruses need to fuse with a host cell membrane in order to deliver their genome into the host cell. In the present study we investigated the entry of coronaviruses (CoVs). CoVs are important pathogens of animals and man with high zoonotic potential as demonstrated by the emergence of SARS- and MERS-CoVs. Previous studies resulted in apparently conflicting results with respect to CoV cell entry, particularly regarding the fusion-activating requirements of the CoV S protein. By combining cell-biological, infection, and fusion assays we demonstrated that murine hepatitis virus (MHV), a prototypic member of the CoV family, enters cells via clathrin-mediated endocytosis. Moreover, although MHV does not depend on a low pH for fusion, the virus was shown to rely on trafficking to lysosomes for proteolytic cleavage of its spike (S) protein and membrane fusion to occur. Based on these results we predicted and subsequently demonstrated that MERS- and feline CoV require cleavage by different proteases and escape the endo/lysosomal system from different compartments. In conclusion, we elucidated the MHV entry pathway in detail and demonstrate that a proteolytic cleavage site in the S protein of different CoVs is an essential determinant of the intracellular site of fusion.
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Affiliation(s)
- Christine Burkard
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Monique H. Verheije
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Oliver Wicht
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Sander I. van Kasteren
- Division of Bio-Organic Synthesis, Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands
| | - Frank J. van Kuppeveld
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Bart L. Haagmans
- Department of Viroscience, Erasmus MC, Rotterdam, The Netherlands
| | - Lucas Pelkmans
- Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland
| | - Peter J. M. Rottier
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Berend Jan Bosch
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
| | - Cornelis A. M. de Haan
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
- * E-mail:
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Abstract
Macropinocytosis is exploited by many pathogens for entry into cells. Coronaviruses (CoVs) such as severe acute respiratory syndrome (SARS) CoV and Middle East respiratory syndrome CoV are important human pathogens; however, macropinocytosis during CoV infection has not been investigated. We demonstrate that the CoVs SARS CoV and murine hepatitis virus (MHV) induce macropinocytosis, which occurs late during infection, is continuous, and is not associated with virus entry. MHV-induced macropinocytosis results in vesicle internalization, as well as extended filopodia capable of fusing with distant cells. MHV-induced macropinocytosis requires fusogenic spike protein on the cell surface and is dependent on epidermal growth factor receptor activation. Inhibition of macropinocytosis reduces supernatant viral titers and syncytia but not intracellular virus titers. These results indicate that macropinocytosis likely facilitates CoV infection through enhanced cell-to-cell spreading. Our studies are the first to demonstrate virus use of macropinocytosis for a role other than entry and suggest a much broader potential exploitation of macropinocytosis in virus replication and host interactions. Importance: Coronaviruses (CoVs), including severe acute respiratory syndrome (SARS) CoV and Middle East respiratory syndrome CoV, are critical emerging human pathogens. Macropinocytosis is induced by many pathogens to enter host cells, but other functions for macropinocytosis in virus replication are unknown. In this work, we show that CoVs induce a macropinocytosis late in infection that is continuous, independent from cell entry, and associated with increased virus titers and cell fusion. Murine hepatitis virus macropinocytosis requires a fusogenic virus spike protein and signals through the epidermal growth factor receptor and the classical macropinocytosis pathway. These studies demonstrate CoV induction of macropinocytosis for a purpose other than entry and indicate that viruses likely exploit macropinocytosis at multiple steps in replication and pathogenesis.
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Park JE, Cruz DJM, Shin HJ. Clathrin- and serine proteases-dependent uptake of porcine epidemic diarrhea virus into Vero cells. Virus Res 2014; 191:21-9. [PMID: 25086180 PMCID: PMC7114442 DOI: 10.1016/j.virusres.2014.07.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2014] [Revised: 07/17/2014] [Accepted: 07/21/2014] [Indexed: 01/22/2023]
Abstract
PEDV enters Vero cells via clathrin-mediated endocytosis. PEDV entry in Vero cells is low pH sensitive. PEDV requires serine proteolysis during entry.
Porcine epidemic diarrhea virus (PEDV), a member of the genus Alphacoronavirus, is a causative agent of porcine enteric disease characterized by acute watery diarrhea and dehydration in sucking piglet. Similar to other coronaviruses, PEDV spike protein mediates its cell entry by binding to cellular receptors and inducing membrane fusion between viral envelopes and cellular membranes. However, the entry mechanism of PEDV is not studied. Here, we determined the entry mechanism of PEDV into Vero cells. Our data confirmed that PEDV entry followed clathrin-mediated endocytosis independence of caveolae-coated pit assembly. The internalized PEDV was co-localized with the clathrin-mediated endocytic marker, but not with the caveolae-mediated endocytic marker. In addition, cells treated with lysosomotropic agents and serine protease inhibitors were resistant to PEDV. Our data revealed that PEDV entry followed clathrin-mediated endocytosis and was dependent on a low pH and serine proteolysis for successful entry into cells.
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Affiliation(s)
- Jung-Eun Park
- Laboratory of Infectious Diseases, College of Veterinary Medicine, South Korea
| | - Deu John M Cruz
- Laboratory of Infectious Diseases, College of Veterinary Medicine, South Korea
| | - Hyun-Jin Shin
- Laboratory of Infectious Diseases, College of Veterinary Medicine, South Korea; Research Institute of Veterinary Medicine, Chungnam National University, South Korea.
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Gierer S, Müller MA, Heurich A, Ritz D, Springstein BL, Karsten CB, Schendzielorz A, Gnirß K, Drosten C, Pöhlmann S. Inhibition of proprotein convertases abrogates processing of the middle eastern respiratory syndrome coronavirus spike protein in infected cells but does not reduce viral infectivity. J Infect Dis 2014; 211:889-97. [PMID: 25057042 PMCID: PMC7107327 DOI: 10.1093/infdis/jiu407] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Middle East respiratory syndrome coronavirus (MERS-CoV) infection is associated with a high case-fatality rate, and the potential pandemic spread of the virus is a public health concern. The spike protein of MERS-CoV (MERS-S) facilitates viral entry into host cells, which depends on activation of MERS-S by cellular proteases. Proteolytic activation of MERS-S during viral uptake into target cells has been demonstrated. However, it is unclear whether MERS-S is also cleaved during S protein synthesis in infected cells and whether cleavage is required for MERS-CoV infectivity. Here, we show that MERS-S is processed by proprotein convertases in MERS-S–transfected and MERS-CoV–infected cells and that several RXXR motifs located at the border between the surface and transmembrane subunit of MERS-S are required for efficient proteolysis. However, blockade of proprotein convertases did not impact MERS-S–dependent transduction of target cells expressing high amounts of the viral receptor, DPP4, and did not modulate MERS-CoV infectivity. These results show that MERS-S is a substrate for proprotein convertases and demonstrate that processing by these enzymes is dispensable for S protein activation. Efforts to inhibit MERS-CoV infection by targeting host cell proteases should therefore focus on enzymes that process MERS-S during viral uptake into target cells.
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Affiliation(s)
| | | | | | - Daniel Ritz
- Institute of Virology, University of Bonn Medical Center
| | | | - Christina B Karsten
- Infection Biology Unit, German Primate Center, Göttingen Institute for Cellular Chemistry, Hannover Medical School, Germany
| | | | - Kerstin Gnirß
- Infection Biology Unit, German Primate Center, Göttingen
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Identification of novel functional regions within the spike glycoprotein of MHV-A59 based on a bioinformatics approach. Virus Res 2014; 189:177-88. [PMID: 24910120 PMCID: PMC4134989 DOI: 10.1016/j.virusres.2014.05.023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Revised: 05/25/2014] [Accepted: 05/27/2014] [Indexed: 01/23/2023]
Abstract
Identification of functional regions within MHV-A59 spike (S) protein through analysis of sequence similarities with FcγR. C547 substitution abolishes the recognition of cleaved S by monoclonal antibodies. Substitution of residues 547 and 581–586 in S prevents the recovery of a viable virus. Amino acid replacements at positions 562/589 and 667/687 in S affect viral replication. Replacement of residue 939 in S affects the fusogenic properties of the virus.
Mouse Hepatitis Virus (MHV) is a single-stranded positive sense RNA virus with the ability to promote acute and chronic diseases in mice. The MHV spike protein (S) is a major virulence determinant which in addition to binding to cellular receptors to mediate cell entry and facilitate virus spread to adjacent cells by cell–cell fusion, also is a molecular mimic of the FcγRII receptor. This molecular mimicry of FcγRII by the MHV S protein is also exhibited by other lineage 2a betacoronaviruses, with the exception of the human coronavirus HCoV-OC43. In this work we undertook a mutational analysis to attempt to identify specific amino acid sequences within the spike glycoprotein crucial for molecular mimicry of FcγRII. Although we were unsuccessful in isolating mutant viruses which were specifically defective in that property, we identified several mutations with interesting phenotypes. Mutation of the cysteine in position 547 to alanine and alanine replacements at residues 581–586 was lethal. Replacing proline 939 with the corresponding HCoV-OC43 residue, leucine, decreased the ability MHV to induce cell–cell fusion, providing experimental support for an earlier proposal that residues 929–944 make up the fusion peptide of the MHV S protein.
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Aydin H, Al-Khooly D, Lee JE. Influence of hydrophobic and electrostatic residues on SARS-coronavirus S2 protein stability: insights into mechanisms of general viral fusion and inhibitor design. Protein Sci 2014; 23:603-17. [PMID: 24519901 PMCID: PMC4005712 DOI: 10.1002/pro.2442] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2013] [Revised: 02/09/2014] [Accepted: 02/10/2014] [Indexed: 12/16/2022]
Abstract
Severe acute respiratory syndrome (SARS) is an acute respiratory disease caused by the SARS-coronavirus (SARS-CoV). SARS-CoV entry is facilitated by the spike protein (S), which consists of an N-terminal domain (S1) responsible for cellular attachment and a C-terminal domain (S2) that mediates viral and host cell membrane fusion. The SARS-CoV S2 is a potential drug target, as peptidomimetics against S2 act as potent fusion inhibitors. In this study, site-directed mutagenesis and thermal stability experiments on electrostatic, hydrophobic, and polar residues to dissect their roles in stabilizing the S2 postfusion conformation was performed. It was shown that unlike the pH-independent retroviral fusion proteins, SARS-CoV S2 is stable over a wide pH range, supporting its ability to fuse at both the plasma membrane and endosome. A comprehensive SARS-CoV S2 analysis showed that specific hydrophobic positions at the C-terminal end of the HR2, rather than electrostatics are critical for fusion protein stabilization. Disruption of the conserved C-terminal hydrophobic residues destabilized the fusion core and reduced the melting temperature by 30°C. The importance of the C-terminal hydrophobic residues led us to identify a 42-residue substructure on the central core that is structurally conserved in all existing CoV S2 fusion proteins (root mean squared deviation = 0.4 Å). This is the first study to identify such a conserved substructure and likely represents a common foundation to facilitate viral fusion. We have discussed the role of key residues in the design of fusion inhibitors and the potential of the substructure as a general target for the development of novel therapeutics against CoV infections.
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Affiliation(s)
- Halil Aydin
- Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
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Identification and characterization of a proteolytically primed form of the murine coronavirus spike proteins after fusion with the target cell. J Virol 2014; 88:4943-52. [PMID: 24554652 DOI: 10.1128/jvi.03451-13] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Enveloped viruses carry highly specialized glycoproteins that catalyze membrane fusion under strict spatial and temporal control. To prevent premature activation after biosynthesis, viral class I fusion proteins adopt a locked conformation and require proteolytic cleavage to render them fusion-ready. This priming step may occur during virus exit from the infected cell, in the extracellular milieu or during entry at or in the next target cell. Proteolytic processing of coronavirus spike (S) fusion proteins during virus entry has been suggested but not yet formally demonstrated, while the nature and functionality of the resulting subunit is still unclear. We used a prototype coronavirus--mouse hepatitis virus (MHV)--to develop a conditional biotinylation assay that enables the specific identification and biochemical characterization of viral S proteins on virions that mediated membrane fusion with the target cell. We demonstrate that MHV S proteins are indeed cleaved upon virus endocytosis, and we identify a novel processing product S2* with characteristics of a fusion-active subunit. The precise cleavage site and the enzymes involved remain to be elucidated. IMPORTANCE Virus entry determines the tropism and is a crucial step in the virus life cycle. We developed an approach to characterize structural components of virus particles after entering new target cells. A prototype coronavirus was used to illustrate how the virus fusion machinery can be controlled.
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Promkuntod N, van Eijndhoven REW, de Vrieze G, Gröne A, Verheije MH. Mapping of the receptor-binding domain and amino acids critical for attachment in the spike protein of avian coronavirus infectious bronchitis virus. Virology 2013; 448:26-32. [PMID: 24314633 PMCID: PMC7111965 DOI: 10.1016/j.virol.2013.09.018] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Revised: 08/21/2013] [Accepted: 09/19/2013] [Indexed: 01/03/2023]
Abstract
The infection of the avian coronavirus infectious bronchitis virus (IBV) is initiated by the binding of the spike glycoprotein S to sialic acids on the chicken host cell. In this study we identified the receptor-binding domain (RBD) of the spike of the prototype IBV strain M41. By analyzing the ability of recombinantly expressed chimeric and truncated spike proteins to bind to chicken tissues, we demonstrate that the N-terminal 253 amino acids of the spike are both required and sufficient for binding to chicken respiratory tract in an α-2,3-sialic acid-dependent manner. Critical amino acids for attachment of M41 spike are present within the N-terminal residues 19-69, which overlap with a hypervariable region in the S1 gene. Our results may help to understand the differences between IBV S1 genotypes and the ultimate pathogenesis of IBV in chickens.
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Affiliation(s)
- N Promkuntod
- Pathology Division, Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584CL Utrecht, The Netherlands
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