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Vallbracht M, Schnell M, Seyfarth A, Fuchs W, Küchler R, Mettenleiter TC, Klupp BG. A Single Amino Acid Substitution in the Transmembrane Domain of Glycoprotein H Functionally Compensates for the Absence of gL in Pseudorabies Virus. Viruses 2023; 16:26. [PMID: 38257727 PMCID: PMC10819001 DOI: 10.3390/v16010026] [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: 11/01/2023] [Revised: 12/12/2023] [Accepted: 12/20/2023] [Indexed: 01/24/2024] Open
Abstract
Herpesvirus entry requires the coordinated action of at least four viral glycoproteins. Virus-specific binding to a cellular receptor triggers a membrane fusion cascade involving the conserved gH/gL complex and gB. Although gB is the genuine herpesvirus fusogen, it requires gH/gL for fusion, but how activation occurs is still unclear. To study the underlying mechanism, we used a gL-deleted pseudorabies virus (PrV) mutant characterized by its limited capability to directly infect neighboring cells that was exploited for several independent serial passages in cell culture. Unlike previous revertants that acquired mutations in the gL-binding N-terminus of gH, we obtained a variant, PrV-ΔgLPassV99, that unexpectedly contained two amino acid substitutions in the gH transmembrane domain (TMD). One of these mutations, I662S, was sufficient to compensate for gL function in virus entry and in in vitro cell-cell fusion assays in presence of wild type gB, but barely for cell-to-cell spread. Additional expression of receptor-binding PrV gD, which is dispensable for cell-cell fusion mediated by native gB, gH and gL, resulted in hyperfusion in combination with gH V99. Overall, our results uncover a yet-underestimated role of the gH TMD in fusion regulation, further shedding light on the complexity of herpesvirus fusion involving all structural domains of the conserved entry glycoproteins.
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Affiliation(s)
- Melina Vallbracht
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (M.V.); (R.K.)
- Schaller Research Groups, Department of Infectious Diseases, Virology, Heidelberg University Hospital, 69120 Heidelberg, Germany
| | - Marina Schnell
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (M.V.); (R.K.)
| | - Annemarie Seyfarth
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (M.V.); (R.K.)
- Department of Hematology, Oncology and Tumor Immunology, CBF, Charité—Universitätsmedizin, Corporate Member of Freie Universität Berlin und Humboldt—Universität zu Berlin, 12200 Berlin, Germany
| | - Walter Fuchs
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (M.V.); (R.K.)
| | - Richard Küchler
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (M.V.); (R.K.)
| | - Thomas C. Mettenleiter
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (M.V.); (R.K.)
| | - Barbara G. Klupp
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany; (M.V.); (R.K.)
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2
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Wu H, Qi H, Wang B, Li M, Qu L, Li S, Luo Y, Li LF, Zheng GL, Qiu HJ, Sun Y. The mutations on the envelope glycoprotein D contribute to the enhanced neurotropism of the pseudorabies virus variant. J Biol Chem 2023; 299:105347. [PMID: 37838171 PMCID: PMC10652121 DOI: 10.1016/j.jbc.2023.105347] [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] [Received: 04/19/2023] [Revised: 09/17/2023] [Accepted: 10/03/2023] [Indexed: 10/16/2023] Open
Abstract
The pseudorabies virus (PRV) TJ strain, a variant of PRV, induces more severe neurological symptoms and higher mortality in piglets and mice than the PRV SC strain isolated in 1980. However, the mechanism underlying responsible for the discrepancy in virulence between these strains remains unclear. Our study investigated the differences in neurotropism between PRV TJ and PRV SC using both in vitro and in vivo models. We discovered that PRV TJ enters neural cells more efficiently than PRV SC. Furthermore, we found that PRV TJ has indistinguishable genomic DNA replication capability and axonal retrograde transport dynamics compared to the PRV SC. To gain deeper insights into the mechanisms underlying these differences, we constructed gene-interchanged chimeric virus constructs and assessed the affinity between envelope glycoprotein B, C, and D (gD) and corresponding receptors. Our findings confirmed that mutations in these envelope proteins, particularly gD, significantly contributed to the heightened attachment and penetration capabilities of PRV TJ. Our study revealed the critical importance of the gDΔR278/P279 and gDV338A in facilitating viral invasion. Furthermore, our observations indicated that mutations in envelope proteins have a more significant impact on viral invasion than on virulence in the mouse model. Our findings provide valuable insights into the roles of natural mutations on the PRV envelope glycoproteins in cell tropism, which sheds light on the relationship between cell tropism and clinical symptoms and offers clues about viral evolution.
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Affiliation(s)
- Hongxia Wu
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Hansong Qi
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Bing Wang
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Mingzhi Li
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Liang Qu
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Su Li
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Yuzi Luo
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Lian-Feng Li
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Guang-Lai Zheng
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China
| | - Hua-Ji Qiu
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China.
| | - Yuan Sun
- State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China.
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3
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Ruan P, Wang M, Cheng A, Zhao X, Yang Q, Wu Y, Zhang S, Tian B, Huang J, Ou X, Gao Q, Sun D, He Y, Wu Z, Zhu D, Jia R, Chen S, Liu M. Mechanism of herpesvirus UL24 protein regulating viral immune escape and virulence. Front Microbiol 2023; 14:1268429. [PMID: 37808279 PMCID: PMC10559885 DOI: 10.3389/fmicb.2023.1268429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 09/08/2023] [Indexed: 10/10/2023] Open
Abstract
Herpesviruses have evolved a series of abilities involved in the process of host infection that are conducive to virus survival and adaptation to the host, such as immune escape, latent infection, and induction of programmed cell death for sustainable infection. The herpesvirus gene UL24 encodes a highly conserved core protein that plays an important role in effective viral infection. The UL24 protein can inhibit the innate immune response of the host by acting on multiple immune signaling pathways during virus infection, and it also plays a key role in the proliferation and pathogenicity of the virus in the later stage of infection. This article reviews the mechanism by which the UL24 protein mediates herpesvirus immune escape and its effects on viral proliferation and virulence by influencing syncytial formation, DNA damage and the cell cycle. Reviewing these studies will enhance our understanding of the pathogenesis of herpesvirus infection and provide evidence for new strategies to combat against viral infection.
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Affiliation(s)
- Peilin Ruan
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Mingshu Wang
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Anchun Cheng
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Xinxin Zhao
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Qiao Yang
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Ying Wu
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Shaqiu Zhang
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Bin Tian
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Juan Huang
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Xumin Ou
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Qun Gao
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Di Sun
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Yu He
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Zhen Wu
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Dekang Zhu
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Renyong Jia
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Shun Chen
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
| | - Mafeng Liu
- Engineering Research Center of Southwest Animal Disease Prevention and Control Technology, Ministry of Education of the People's Republic of China, Chengdu, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Chengdu, China
- International Joint Research Center for Animal Disease Prevention and Control of Sichuan Province, Chengdu, China
- Institute of Veterinary Medicine and Immunology, Sichuan Agricultural University, Chengdu, China
- Research Center of Avian Disease, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu, China
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Ye N, Feng W, Fu T, Tang D, Zeng Z, Wang B. Membrane fusion, potential threats, and natural antiviral drugs of pseudorabies virus. Vet Res 2023; 54:39. [PMID: 37131259 PMCID: PMC10152797 DOI: 10.1186/s13567-023-01171-z] [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: 11/09/2022] [Accepted: 04/04/2023] [Indexed: 05/04/2023] Open
Abstract
Pseudorabies virus (PrV) can infect several animals and causes severe economic losses in the swine industry. Recently, human encephalitis or endophthalmitis caused by PrV infection has been frequently reported in China. Thus, PrV can infect animals and is becoming a potential threat to human health. Although vaccines and drugs are the main strategies to prevent and treat PrV outbreaks, there is no specific drug, and the emergence of new PrV variants has reduced the effectiveness of classical vaccines. Therefore, it is challenging to eradicate PrV. In the present review, the membrane fusion process of PrV entering target cells, which is conducive to revealing new therapeutic and vaccine strategies for PrV, is presented and discussed. The current and potential PrV pathways of infection in humans are analyzed, and it is hypothesized that PrV may become a zoonotic agent. The efficacy of chemically synthesized drugs for treating PrV infections in animals and humans is unsatisfactory. In contrast, multiple extracts of traditional Chinese medicine (TCM) have shown anti-PRV activity, exerting its effects in different phases of the PrV life-cycle and suggesting that TCM compounds may have great potential against PrV. Overall, this review provides insights into developing effective anti-PrV drugs and emphasizes that human PrV infection should receive more attention.
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Affiliation(s)
- Ni Ye
- College of Animal Science, Guizhou University, Guiyang, 550025, China
| | - Wei Feng
- College of Animal Science, Guizhou University, Guiyang, 550025, China
| | - Tiantian Fu
- College of Animal Science, Guizhou University, Guiyang, 550025, China
| | - Deyuan Tang
- College of Animal Science, Guizhou University, Guiyang, 550025, China
| | - Zhiyong Zeng
- College of Animal Science, Guizhou University, Guiyang, 550025, China
| | - Bin Wang
- College of Animal Science, Guizhou University, Guiyang, 550025, China.
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Fan Q, Hippler DP, Yang Y, Longnecker R, Connolly SA. Multiple Sites on Glycoprotein H (gH) Functionally Interact with the gB Fusion Protein to Promote Fusion during Herpes Simplex Virus (HSV) Entry. mBio 2023; 14:e0336822. [PMID: 36629412 PMCID: PMC9973363 DOI: 10.1128/mbio.03368-22] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Accepted: 12/08/2022] [Indexed: 01/12/2023] Open
Abstract
Enveloped virus entry requires fusion of the viral envelope with a host cell membrane. Herpes simplex virus 1 (HSV-1) entry is mediated by a set of glycoproteins that interact to trigger the viral fusion protein glycoprotein B (gB). In the current model, receptor-binding by gD signals a gH/gL heterodimer to trigger a refolding event in gB that fuses the membranes. To explore functional interactions between gB and gH/gL, we used a bacterial artificial chromosome (BAC) to generate two HSV-1 mutants that show a small plaque phenotype due to changes in gB. We passaged the viruses to select for restoration of plaque size and analyzed second-site mutations that arose in gH. HSV-1 gB was replaced either by gB from saimiriine herpesvirus 1 (SaHV-1) or by a mutant form of HSV-1 gB with three alanine substitutions in domain V (gB3A). To shift the selective pressure away from gB, the gB3A virus was passaged in cells expressing gB3A. Sequencing of passaged viruses identified two interesting mutations in gH, including gH-H789Y in domain IV and gH-S830N in the cytoplasmic tail (CT). Characterization of these gH mutations indicated they are responsible for the enhanced plaque size. Rather than being globally hyperfusogenic, both gH mutations partially rescued function of the specific gB version present during their selection. These sites may represent functional interaction sites on gH/gL for gB. gH-H789 may alter the positioning of a membrane-proximal flap in the gH ectodomain, whereas gH-S830 may contribute to an interaction between the gB and gH CTs. IMPORTANCE Enveloped viruses enter cells by fusing their envelope with the host cell membrane. Herpes simplex virus 1 (HSV-1) entry requires the coordinated interaction of several viral glycoproteins, including gH/gL and gB. gH/gL and gB are essential for virus replication and both proteins are targets of neutralizing antibodies. gB fuses the membranes after being activated by gH/gL, but the details of how gH/gL activates gB are not known. This study examined the gH/gL-gB interaction using HSV-1 mutants that displayed reduced virus entry due to changes in gB. The mutant viruses were grown over time to select for additional mutations that could partially restore entry. Two mutations in gH (H789Y and S830N) were identified. The positions of the mutations in gH/gL may represent sites that contribute to gB activation during virus entry.
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Affiliation(s)
- Qing Fan
- Department of Microbiology-Immunology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Daniel P. Hippler
- Department of Health Sciences, DePaul University, Chicago, Illinois, USA
- Department of Biological Sciences, DePaul University, Chicago, Illinois, USA
| | - Yueqi Yang
- Yuanpei College, Peking University, Beijing, China
| | - Richard Longnecker
- Department of Microbiology-Immunology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Sarah A. Connolly
- Department of Health Sciences, DePaul University, Chicago, Illinois, USA
- Department of Biological Sciences, DePaul University, Chicago, Illinois, USA
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Pataki Z, Sanders EK, Heldwein EE. A surface pocket in the cytoplasmic domain of the herpes simplex virus fusogen gB controls membrane fusion. PLoS Pathog 2022; 18:e1010435. [PMID: 35767585 PMCID: PMC9275723 DOI: 10.1371/journal.ppat.1010435] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2022] [Revised: 07/12/2022] [Accepted: 06/03/2022] [Indexed: 12/27/2022] Open
Abstract
Membrane fusion during the entry of herpesviruses is carried out by the viral fusogen gB that is activated by its partner protein gH in some manner. The fusogenic activity of gB is controlled by its cytoplasmic (or intraviral) domain (gBCTD) and, according to the current model, the gBCTD is a trimeric, inhibitory clamp that restrains gB in the prefusion conformation. But how the gBCTD clamp is released by gH is unclear. Here, we identified two new regulatory elements within gB and gH from the prototypical herpes simplex virus 1: a surface pocket within the gBCTD and residue V831 within the gH cytoplasmic tail. Mutagenesis and structural modeling suggest that gH V831 interacts with the gB pocket. The gB pocket is located above the interface between adjacent protomers, and we hypothesize that insertion of the gH V831 wedge into the pocket serves to push the protomers apart, which releases the inhibitory clamp. In this manner, gH activates the fusogenic activity of gB. Both gB and gH are conserved across all herpesviruses, and this activation mechanism could be used by other gB homologs. Our proposed mechanism emphasizes a central role for the cytoplasmic regions in regulating the activity of a viral fusogen. Herpes simplex virus 1 (HSV-1) establishes lifelong infections in over a half of people and causes diseases ranging from oral or genital sores to blindness and brain inflammation. No vaccines or curative treatments are currently available. To infect cells, HSV-1 must first penetrate them by merging its lipid envelope with the membrane of the target cell. This process requires the collective actions of several viral and cellular proteins, notably, viral glycoproteins B and H (gB and gH). gH is thought to activate the fusogenic function of gB, but how the two proteins interact is unclear. Here, using mutational analysis, we have identified two new functional elements within the cytoplasmic regions of gB and gH: a surface pocket in gB and a single residue in gH, both of which are important for membrane fusion. Based on structural modeling, we propose that the gB pocket is the binding site for the gH residue, and that their interaction activates gB to cause membrane fusion. These findings extend our knowledge of the HSV-1 membrane fusion mechanism. Mechanistic understanding of HSV-1 entry is essential for understanding its pathogenesis and developing new strategies to prevent infections.
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Affiliation(s)
- Zemplen Pataki
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts, United States of America.,Graduate Program in Molecular Microbiology, Graduate School of Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
| | - Erin K Sanders
- Graduate Program in Cellular, Molecular, and Developmental Biology, Graduate School of Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
| | - Ekaterina E Heldwein
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts, United States of America.,Graduate Program in Molecular Microbiology, Graduate School of Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America.,Graduate Program in Cellular, Molecular, and Developmental Biology, Graduate School of Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
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Vallbracht M, Klupp BG, Mettenleiter TC. Influence of N-glycosylation on Expression and Function of Pseudorabies Virus Glycoprotein gB. Pathogens 2021; 10:61. [PMID: 33445487 PMCID: PMC7827564 DOI: 10.3390/pathogens10010061] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 01/07/2021] [Accepted: 01/07/2021] [Indexed: 01/13/2023] Open
Abstract
Envelope glycoprotein (g)B is conserved throughout the Herpesviridae and mediates fusion of the viral envelope with cellular membranes for infectious entry and spread. Like all viral envelope fusion proteins, gB is modified by asparagine (N)-linked glycosylation. Glycans can contribute to protein function, intracellular transport, trafficking, structure and immune evasion. gB of the alphaherpesvirus pseudorabies virus (PrV) contains six consensus sites for N-linked glycosylation, but their functional relevance is unknown. Here, we investigated the occupancy and functional relevance of N-glycosylation sites in PrV gB. To this end, all predicted N-glycosylation sites were inactivated either singly or in combination by the introduction of conservative mutations (N➔Q). The resulting proteins were tested for expression, fusion activity in cell-cell fusion assays and complementation of a gB-deficient PrV mutant. Our results indicate that all six sites are indeed modified. However, while glycosylation at most sites was dispensable for gB expression and fusogenicity, inactivation of N154 and N700 affected gB processing by furin cleavage and surface localization. Although all single mutants were functional in cell-cell fusion and viral entry, simultaneous inactivation of all six N-glycosylation sites severely impaired fusion activity and viral entry, suggesting a critical role of N-glycans for maintaining gB structure and function.
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Affiliation(s)
| | | | - Thomas C. Mettenleiter
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany; (M.V.); (B.G.K.)
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Su X, Wang Q, Wen Y, Jiang S, Lu L. Protein- and Peptide-Based Virus Inactivators: Inactivating Viruses Before Their Entry Into Cells. Front Microbiol 2020; 11:1063. [PMID: 32523582 PMCID: PMC7261908 DOI: 10.3389/fmicb.2020.01063] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2019] [Accepted: 04/29/2020] [Indexed: 12/20/2022] Open
Abstract
Infectious diseases caused by human immunodeficiency virus (HIV) and other highly pathogenic enveloped viruses, have threatened the global public health. Most antiviral drugs act as passive defenders to inhibit viral replication inside the cell, while a few of them function as gate keepers to combat viruses outside the cell, including fusion inhibitors, e.g., enfuvirtide, and receptor antagonists, e.g., maraviroc, as well as virus inactivators (including attachment inhibitors). Different from fusion inhibitors and receptor antagonists that must act in the presence of target cells, virus inactivators can actively inactivate cell-free virions in the blood, through interaction with one or more sites in the envelope glycoproteins (Envs) on virions. Notably, a number of protein- and peptide-based virus inactivators (PPVIs) under development are expected to have a better utilization rate than the current antiviral drugs and be safer for in vivo human application than the chemical-based virus inactivators. Here we have highlighted recent progress in developing PPVIs against several important enveloped viruses, including HIV, influenza virus, Zika virus (ZIKV), dengue virus (DENV), and herpes simplex virus (HSV), and the potential use of PPVIs for urgent treatment of infection by newly emerging or re-emerging viruses.
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Affiliation(s)
- Xiaojie Su
- Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Qian Wang
- Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Yumei Wen
- Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Shibo Jiang
- Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences, Fudan University, Shanghai, China.,Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY, United States
| | - Lu Lu
- Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences, Fudan University, Shanghai, China
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Vallbracht M, Backovic M, Klupp BG, Rey FA, Mettenleiter TC. Common characteristics and unique features: A comparison of the fusion machinery of the alphaherpesviruses Pseudorabies virus and Herpes simplex virus. Adv Virus Res 2019; 104:225-281. [PMID: 31439150 DOI: 10.1016/bs.aivir.2019.05.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Membrane fusion is a fundamental biological process that allows different cellular compartments delimited by a lipid membrane to release or exchange their respective contents. Similarly, enveloped viruses such as alphaherpesviruses exploit membrane fusion to enter and infect their host cells. For infectious entry the prototypic human Herpes simplex viruses 1 and 2 (HSV-1 and -2, collectively termed HSVs) and the porcine Pseudorabies virus (PrV) utilize four different essential envelope glycoproteins (g): the bona fide fusion protein gB and the regulatory heterodimeric gH/gL complex that constitute the "core fusion machinery" conserved in all members of the Herpesviridae; and the subfamily specific receptor binding protein gD. These four components mediate attachment and fusion of the virion envelope with the host cell plasma membrane through a tightly regulated sequential activation process. Although PrV and the HSVs are closely related and employ the same set of glycoproteins for entry, they show remarkable differences in the requirements for fusion. Whereas the HSVs strictly require all four components for membrane fusion, PrV can mediate cell-cell fusion without gD. Moreover, in contrast to the HSVs, PrV provides a unique opportunity for reversion analyses of gL-negative mutants by serial cell culture passaging, due to a limited cell-cell spread capacity of gL-negative PrV not observed in the HSVs. This allows a more direct analysis of the function of gH/gL during membrane fusion. Unraveling the molecular mechanism of herpesvirus fusion has been a goal of fundamental research for years, and yet important mechanistic details remain to be uncovered. Nevertheless, the elucidation of the crystal structures of all key players involved in PrV and HSV membrane fusion, coupled with a wealth of functional data, has shed some light on this complex puzzle. In this review, we summarize and discuss the contemporary knowledge on the molecular mechanism of entry and membrane fusion utilized by the alphaherpesvirus PrV, and highlight similarities but also remarkable differences in the requirements for fusion between PrV and the HSVs.
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Affiliation(s)
- Melina Vallbracht
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald - Insel Riems, Germany.
| | - Marija Backovic
- Institut Pasteur, Unité de Virologie Structurale, UMR3569 (CNRS), Paris, France
| | - Barbara G Klupp
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald - Insel Riems, Germany
| | - Felix A Rey
- Institut Pasteur, Unité de Virologie Structurale, UMR3569 (CNRS), Paris, France
| | - Thomas C Mettenleiter
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald - Insel Riems, Germany
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Vallbracht M, Fuchs W, Klupp BG, Mettenleiter TC. Functional Relevance of the Transmembrane Domain and Cytoplasmic Tail of the Pseudorabies Virus Glycoprotein H for Membrane Fusion. J Virol 2018; 92:e00376-18. [PMID: 29618646 PMCID: PMC5974499 DOI: 10.1128/jvi.00376-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 03/29/2018] [Indexed: 12/18/2022] Open
Abstract
Herpesvirus membrane fusion depends on the core fusion machinery, comprised of glycoproteins B (gB) and gH/gL. Although gB structurally resembles autonomous class III fusion proteins, it strictly depends on gH/gL to drive membrane fusion. Whether the gH/gL complex needs to be membrane anchored to fulfill its function and which role the gH cytoplasmic (CD) and transmembrane domains (TMD) play in fusion is unclear. While the gH CD and TMD play an important role during infection, soluble gH/gL of herpes simplex virus 1 (HSV-1) seems to be sufficient to mediate cell-cell fusion in transient assays, arguing against an essential contribution of the CD and TMD. To shed more light on this apparent discrepancy, we investigated the role of the CD and TMD of the related alphaherpesvirus pseudorabies virus (PrV) gH. For this purpose, we expressed C-terminally truncated and soluble gH and replaced the TMD with a glycosylphosphatidylinositol (gpi) anchor. We also generated chimeras containing the TMD and/or CD of PrV gD or HSV-1 gH. Proteins were characterized in cell-based fusion assays and during virus infection. Although truncation of the CD resulted in decreased membrane fusion activity, the mutant proteins still supported replication of gH-negative PrV, indicating that the PrV gH CD is dispensable for viral replication. In contrast, PrV gH lacking the TMD, membrane-anchored via a lipid linker, or comprising the PrV gD TMD were nonfunctional, highlighting the essential role of the gH TMD for function. Interestingly, despite low sequence identity, the HSV-1 gH TMD could substitute for the PrV gH TMD, pointing to functional conservation.IMPORTANCE Enveloped viruses depend on membrane fusion for virus entry. While this process can be mediated by only one or two proteins, herpesviruses depend on the concerted action of at least three different glycoproteins. Although gB has features of bona fide fusion proteins, it depends on gH and its complex partner, gL, for fusion. Whether gH/gL prevents premature fusion or actively triggers gB-mediated fusion is unclear, and there are contradictory results on whether gH/gL function requires stable membrane anchorage or whether the ectodomains alone are sufficient. Our results show that in pseudorabies virus gH, the transmembrane anchor plays an essential role for gB-mediated fusion while the cytoplasmic tail is not strictly required.
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Affiliation(s)
- Melina Vallbracht
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
| | - Walter Fuchs
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
| | - Barbara G Klupp
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
| | - Thomas C Mettenleiter
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
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Azab W, Osterrieder K. Initial Contact: The First Steps in Herpesvirus Entry. ADVANCES IN ANATOMY EMBRYOLOGY AND CELL BIOLOGY 2018; 223:1-27. [PMID: 28528437 DOI: 10.1007/978-3-319-53168-7_1] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The entry process of herpesviruses into host cells is complex and highly variable. It involves a sequence of well-orchestrated events that begin with virus attachment to glycan-containing proteinaceous structures on the cell surface. This initial contact tethers virus particles to the cell surface and results in a cascade of molecular interactions, including the tight interaction of viral envelope glycoproteins to specific cell receptors. These interactions trigger intracellular signaling and finally virus penetration after fusion of the viral envelope with cellular membranes. Based on the engaged cellular receptors and co-receptors, and the subsequent signaling cascades, the entry pathway will be decided on the spot. A number of viral glycoproteins and many cellular receptors and molecules have been identified as players in one or several of these events during virus entry. This chapter will review viral glycoproteins, cellular receptors and signaling cascades associated with the very first interactions of herpesviruses with their target cells.
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Affiliation(s)
- Walid Azab
- Institut für Virologie, Robert von Ostertag-Haus, Zentrum für Infektionsmedizin, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163, Berlin, Germany.
| | - Klaus Osterrieder
- Institut für Virologie, Robert von Ostertag-Haus, Zentrum für Infektionsmedizin, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163, Berlin, Germany
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Vallbracht M, Rehwaldt S, Klupp BG, Mettenleiter TC, Fuchs W. Functional Role of N-Linked Glycosylation in Pseudorabies Virus Glycoprotein gH. J Virol 2018; 92:e00084-18. [PMID: 29437979 PMCID: PMC5899193 DOI: 10.1128/jvi.00084-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 02/02/2018] [Indexed: 12/27/2022] Open
Abstract
Many viral envelope proteins are modified by asparagine (N)-linked glycosylation, which can influence their structure, physicochemical properties, intracellular transport, and function. Here, we systematically analyzed the functional relevance of N-linked glycans in the alphaherpesvirus pseudorabies virus (PrV) glycoprotein H (gH), which is an essential component of the conserved core herpesvirus fusion machinery. Upon gD-mediated receptor binding, the heterodimeric complex of gH and gL activates gB to mediate fusion of the viral envelope with the host cell membrane for viral entry. gH contains five potential N-linked glycosylation sites at positions 77, 162, 542, 604, and 627, which were inactivated by conservative mutations (asparagine to glutamine) singly or in combination. The mutated proteins were tested for correct expression and fusion activity. Additionally, the mutated gH genes were inserted into the PrV genome for analysis of function during virus infection. Our results demonstrate that all five sites are glycosylated. Inactivation of the PrV-specific N77 or the conserved N627 resulted in significantly reduced in vitro fusion activity, delayed penetration kinetics, and smaller virus plaques. Moreover, substitution of N627 greatly affected transport of gH in transfected cells, resulting in endoplasmic reticulum (ER) retention and reduced surface expression. In contrast, mutation of N604, which is conserved in the Varicellovirus genus, resulted in enhanced in vitro fusion activity and viral cell-to-cell spread. These results demonstrate a role of the N-glycans in proper localization and function of PrV gH. However, even simultaneous inactivation of all five N-glycosylation sites of gH did not severely inhibit formation of infectious virus particles.IMPORTANCE Herpesvirus infection requires fusion of the viral envelope with cellular membranes, which involves the conserved fusion machinery consisting of gB and the heterodimeric gH/gL complex. The bona fide fusion protein gB depends on the presence of the gH/gL complex for activation. Viral envelope glycoproteins, such as gH, usually contain N-glycans, which can have a strong impact on their folding, transport, and functions. Here, we systematically analyzed the functional relevance of all five predicted N-linked glycosylation sites in the alphaherpesvirus pseudorabies virus (PrV) gH. Despite the fact that mutation of specific sites affected gH transport, in vitro fusion activity, and cell-to-cell spread and resulted in delayed penetration kinetics, even simultaneous inactivation of all five N-glycosylation sites of gH did not severely inhibit formation of infectious virus particles. Thus, our results demonstrate a modulatory but nonessential role of N-glycans for gH function.
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Affiliation(s)
- Melina Vallbracht
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
| | - Sascha Rehwaldt
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
| | - Barbara G Klupp
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
| | - Thomas C Mettenleiter
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
| | - Walter Fuchs
- Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
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Functional Relevance of the N-Terminal Domain of Pseudorabies Virus Envelope Glycoprotein H and Its Interaction with Glycoprotein L. J Virol 2017; 91:JVI.00061-17. [PMID: 28228592 DOI: 10.1128/jvi.00061-17] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Accepted: 02/15/2017] [Indexed: 01/17/2023] Open
Abstract
Several envelope glycoproteins are involved in herpesvirus entry into cells, direct cell-to-cell spread, and induction of cell fusion. The membrane fusion protein glycoprotein B (gB) and the presumably gB-activating heterodimer gH/gL are essential for these processes and conserved throughout the Herpesviridae However, after extended cell culture passage of gL-negative mutants of the alphaherpesvirus pseudorabies virus (PrV), phenotypic revertants could be isolated which had acquired spontaneous mutations affecting the gL-interacting N-terminal part of the gH ectodomain (gDH and gHB4.1) (B. G. Klupp and T. C. Mettenleiter, J Virol 73:3014-3022, 1999; C. Schröter, M. Vallbracht, J. Altenschmidt, S. Kargoll, W. Fuchs, B. G. Klupp, and T. C. Mettenleiter, J Virol 90:2264-2272, 2016). To investigate the functional relevance of this part of gH in more detail, we introduced an in-frame deletion of 66 codons at the 5' end of the plasmid-cloned gH gene (gH32/98). The N-terminal signal peptide was retained, and the deletion did not affect expression or processing of gH but abrogated its function in in vitro fusion assays. Insertion of the engineered gH gene into the PrV genome resulted in a defective mutant (pPrV-gH32/98K), which was incapable of entry and spread. Interestingly, in vitro activity of mutated gH32/98 was restored when it was coexpressed with hyperfusogenic gBB4.1, obtained from a passaged gL deletion mutant of PrV. Moreover, the entry and spread defects of pPrV-gH32/98K were compensated by the mutations in gBB4.1 in cis, as well as in trans, independent of gL. Thus, PrV gL and the gL-interacting domain of gH are not strictly required for function.IMPORTANCE Membrane fusion is crucial for infectious entry and spread of enveloped viruses. While many enveloped viruses require only one or two proteins for receptor binding and membrane fusion, herpesvirus infection depends on several envelope glycoproteins. Besides subfamily-specific receptor binding proteins, the core fusion machinery consists of the conserved fusion protein gB and the gH/gL complex. The role of the latter is unclear, but it is hypothesized to interact with gB for fusion activation. Using isogenic virus recombinants, we demonstrate here that gL and the gL-binding domain of PrV gH are not strictly required for membrane fusion during virus entry and spread when concomitantly mutations in gB are present which increase its fusogenicity. Thus, our results strongly support the notion of a functional gB-gH interaction during the fusion process.
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