Herpesviruses are ubiquitous, double-stranded DNA, enveloped viruses that establish lifelong infections and cause a range of diseases. Entry into host cells requires binding of the virus to specific receptors, followed by the coordinated action of multiple viral entry glycoproteins to trigger membrane fusion. Although the core fusion machinery is conserved for all herpesviruses, each species uses distinct receptors and receptor-binding glycoproteins. Structural studies of the prototypical herpesviruses herpes simplex virus 1 (HSV-1), HSV-2, human cytomegalovirus (HCMV) and Epstein–Barr virus (EBV) entry glycoproteins have defined the interaction sites for glycoprotein complexes and receptors, and have revealed conformational changes that occur on receptor binding. Recent crystallography and electron microscopy studies have refined our model of herpesvirus entry into cells, clarifying both the conserved features and the unique features. In this Review, we discuss recent insights into herpesvirus entry by analysing the structures of entry glycoproteins, including the diverse receptor-binding glycoproteins (HSV-1 glycoprotein D (gD), EBV glycoprotein 42 (gp42) and HCMV gH–gL–gO trimer and gH–gL–UL128–UL130–UL131A pentamer), as well gH–gL and the fusion protein gB, which are conserved in all herpesviruses.
Subscribe to Journal
Get full journal access for 1 year
only $21.58 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Vallbracht, M., Backovic, M., Klupp, B. G., Rey, F. A. & Mettenleiter, T. C. Common characteristics and unique features: a comparison of the fusion machinery of the alphaherpesviruses Pseudorabies virus and Herpes simplex virus. Adv. Virus Res. 104, 225–281 (2019).
Mohl, B. S., Chen, J. & Longnecker, R. Gammaherpesvirus entry and fusion: a tale how two human pathogenic viruses enter their host cells. Adv. Virus Res. 104, 313–343 (2019).
Nishimura, M. & Mori, Y. Entry of betaherpesviruses. Adv. Virus Res. 104, 283–312 (2019).
Atanasiu, D., Saw, W. T., Cohen, G. H. & Eisenberg, R. J. Cascade of events governing cell-cell fusion induced by herpes simplex virus glycoproteins gD, gH/gL, and gB. J. Virol. 84, 12292–12299 (2010).
Nicola, A. V. Herpesvirus entry into host cells mediated by endosomal low pH. Traffic 17, 965–975 (2016).
Gerna, G., Baldanti, F. & Revello, M. G. Pathogenesis of human cytomegalovirus infection and cellular targets. Hum. Immunol. 65, 381–386 (2004).
Ryckman, B. J., Jarvis, M. A., Drummond, D. D., Nelson, J. A. & Johnson, D. C. Human cytomegalovirus entry into epithelial and endothelial cells depends on genes UL128 to UL150 and occurs by endocytosis and low-pH fusion. J. Virol. 80, 710–722 (2006).
Compton, T., Nepomuceno, R. R. & Nowlin, D. M. Human cytomegalovirus penetrates host cells by pH-independent fusion at the cell surface. Virology 191, 387–395 (1992).
Hutt-Fletcher, L. M. Epstein-Barr virus entry. J. Virol. 81, 7825–7832 (2007).
Miller, N. & Hutt-Fletcher, L. M. Epstein-Barr virus enters B cells and epithelial cells by different routes. J. Virol. 66, 3409–3414 (1992).
Di Giovine, P. et al. Structure of herpes simplex virus glycoprotein D bound to the human receptor nectin-1. PLoS Pathog. 7, e1002277 (2011).
Krummenacher, C. et al. Structure of unliganded HSV gD reveals a mechanism for receptor-mediated activation of virus entry. EMBO J. 24, 4144–4153 (2005). Compares the crystal structure of unbound HSV-1 gD with that of the previously determined gD–HVEM complex, revealing a conformational change that occurs on receptor-binding.
Carfi, A. et al. Herpes simplex virus glycoprotein D bound to the human receptor HveA. Mol. Cell 8, 169–179 (2001).
Mullen, M. M., Haan, K. M., Longnecker, R. & Jardetzky, T. S. Structure of the Epstein-Barr virus gp42 protein bound to the MHC class II receptor HLA-DR1. Mol. Cell 9, 375–385 (2002).
Kirschner, A. N., Sorem, J., Longnecker, R. & Jardetzky, T. S. Structure of Epstein-Barr virus glycoprotein 42 suggests a mechanism for triggering receptor-activated virus entry. Structure 17, 223–233 (2009).
Sathiyamoorthy, K. et al. Structural basis for Epstein-Barr virus host cell tropism mediated by gp42 and gHgL entry glycoproteins. Nat. Commun. 7, 13557 (2016). Reports the crystal structure of the EBV gp42–gH–gL complex, demonstrating that the N terminus of gp42 spans the length of gH.
Chandramouli, S. et al. Structural basis for potent antibody-mediated neutralization of human cytomegalovirus. Sci. Immunol. https://doi.org/10.1126/sciimmunol.aan1457 (2017). Reports the crystal structure of the HCMV pentamer, demonstrating that HCMV gH–gL folds similarly to EBV gH–gL and UL128–UL130–UL131A binds to an extension in gL.
Ciferri, C. et al. Structural and biochemical studies of HCMV gH/gL/gO and Pentamer reveal mutually exclusive cell entry complexes. Proc. Natl Acad. Sci. USA 112, 1767–1772 (2015). EM reconstructions of the HCMV trimer and pentamer complexes demonstrate that both gO and UL128–UL130–UL131A dock at the tip of gH–gL.
Martinez-Martin, N. et al. An unbiased screen for human cytomegalovirus identifies neuropilin-2 as a central viral receptor. Cell 174, 1158–1171 e1119 (2018). Identifies NRP2 as an HCMV receptor and shows that this receptor binds to the distal end of the pentamer by EM reconstruction.
Kabanova, A. et al. Platelet-derived growth factor-alpha receptor is the cellular receptor for human cytomegalovirus gHgLgO trimer. Nat. Microbiol. 1, 16082 (2016). Identifies PDGFRα as an HCMV receptor and shows that this receptor binds to the distal end of the trimer by EM.
Szakonyi, G. et al. Structure of the Epstein-Barr virus major envelope glycoprotein. Nat. Struct. Mol. Biol. 13, 996–1001 (2006).
Oliver, S. L., Yang, E. & Arvin, A. M. Varicella-zoster virus glycoproteins: entry, replication, and pathogenesis. Curr. Clin. Microbiol. Rep. 3, 204–215 (2016).
Geraghty, R. J., Krummenacher, C., Cohen, G. H., Eisenberg, R. J. & Spear, P. G. Entry of alphaherpesviruses mediated by poliovirus receptor-related protein 1 and poliovirus receptor. Science 280, 1618–1620 (1998).
Krummenacher, C. et al. Comparative usage of herpesvirus entry mediator A and nectin-1 by laboratory strains and clinical isolates of herpes simplex virus. Virology 322, 286–299 (2004).
Warner, M. S. et al. A cell surface protein with herpesvirus entry activity (HveB) confers susceptibility to infection by mutants of herpes simplex virus type 1, herpes simplex virus type 2, and pseudorabies virus. Virology 246, 179–189 (1998).
Montgomery, R. I., Warner, M. S., Lum, B. J. & Spear, P. G. Herpes simplex virus-1 entry into cells mediated by a novel member of the TNF/NGF receptor family. Cell 87, 427–436 (1996).
Shukla, D. et al. A novel role for 3-O-sulfated heparan sulfate in herpes simplex virus 1 entry. Cell 99, 13–22 (1999).
Lee, C. C. et al. Structural basis for the antibody neutralization of herpes simplex virus. Acta Crystallogr. D Biol. Crystallogr. 69, 1935–1945 (2013).
Li, A. et al. Structural basis of nectin-1 recognition by pseudorabies virus glycoprotein D. PLoS Pathog. 13, e1006314 (2017).
Lu, G. et al. Crystal structure of herpes simplex virus 2 gD bound to nectin-1 reveals a conserved mode of receptor recognition. J. Virol. 88, 13678–13688 (2014).
Connolly, S. A. et al. Glycoprotein D homologs in herpes simplex virus type 1, pseudorabies virus, and bovine herpes virus type 1 bind directly to human HveC (nectin-1) with different affinities. Virology 280, 7–18 (2001).
Krummenacher, C. et al. Herpes simplex virus glycoprotein D can bind to poliovirus receptor-related protein 1 or herpesvirus entry mediator, two structurally unrelated mediators of virus entry. J. Virol. 72, 7064–7074 (1998).
Whitbeck, J. C. et al. The major neutralizing antigenic site on herpes simplex virus glycoprotein D overlaps a receptor-binding domain. J. Virol. 73, 9879–9890 (1999).
Yoon, M., Zago, A., Shukla, D. & Spear, P. G. Mutations in the N termini of herpes simplex virus type 1 and 2 gDs alter functional interactions with the entry/fusion receptors HVEM, nectin-2, and 3-O-sulfated heparan sulfate but not with nectin-1. J. Virol. 77, 9221–9231 (2003).
Willis, S. H. et al. Examination of the kinetics of herpes simplex virus glycoprotein D binding to the herpesvirus entry mediator, using surface plasmon resonance. J. Virol. 72, 5937–5947 (1998).
Krummenacher, C. et al. The first immunoglobulin-like domain of HveC is sufficient to bind herpes simplex virus gD with full affinity, while the third domain is involved in oligomerization of HveC. J. Virol. 73, 8127–8137 (1999).
Lazear, E. et al. Engineered disulfide bonds in herpes simplex virus type 1 gD separate receptor binding from fusion initiation and viral entry. J. Virol. 82, 700–709 (2008).
Sathiyamoorthy, K. et al. Assembly and architecture of the EBV B cell entry triggering complex. PLoS Pathog. 10, e1004309 (2014). EM reconstructions of the gp42–HLA–gH–gL complex reveal open and closed conformations.
Sorem, J., Jardetzky, T. S. & Longnecker, R. Cleavage and secretion of Epstein-Barr virus glycoprotein 42 promote membrane fusion with B lymphocytes. J. Virol. 83, 6664–6672 (2009).
Kirschner, A. N., Lowrey, A. S., Longnecker, R. & Jardetzky, T. S. Binding-site interactions between Epstein-Barr virus fusion proteins gp42 and gH/gL reveal a peptide that inhibits both epithelial and B-cell membrane fusion. J. Virol. 81, 9216–9229 (2007).
Silva, A. L., Omerovic, J., Jardetzky, T. S. & Longnecker, R. Mutational analyses of Epstein-Barr virus glycoprotein 42 reveal functional domains not involved in receptor binding but required for membrane fusion. J. Virol. 78, 5946–5956 (2004).
Zhou, M., Lanchy, J. M. & Ryckman, B. J. Human cytomegalovirus gH/gL/gO promotes the fusion step of entry into all cell types, whereas gH/gL/UL128–131 broadens virus tropism through a distinct mechanism. J. Virol. 89, 8999–9009 (2015).
Wang, D. & Shenk, T. Human cytomegalovirus UL131 open reading frame is required for epithelial cell tropism. J. Virol. 79, 10330–10338 (2005).
Zhou, M., Yu, Q., Wechsler, A. & Ryckman, B. J. Comparative analysis of gO isoforms reveals that strains of human cytomegalovirus differ in the ratio of gH/gL/gO and gH/gL/UL128–131 in the virion envelope. J. Virol. 87, 9680–9690 (2013).
Wu, Y. et al. Human cytomegalovirus glycoprotein complex gH/gL/gO uses PDGFR-alpha as a key for entry. PLoS Pathog. 13, e1006281 (2017).
E, X. et al. OR14I1 is a receptor for the human cytomegalovirus pentameric complex and defines viral epithelial cell tropism. Proc. Natl Acad. Sci. USA 116, 7043–7052 (2019).
Vanarsdall, A. L. et al. CD147 promotes entry of pentamer-expressing human cytomegalovirus into epithelial and endothelial cells. mBio https://doi.org/10.1128/mBio.00781-18 (2018).
Liu, J., Jardetzky, T. S., Chin, A. L., Johnson, D. C. & Vanarsdall, A. L. The human cytomegalovirus trimer and pentamer promote sequential steps in entry into epithelial and endothelial cells at cell surfaces and endosomes. J. Virol. https://doi.org/10.1128/JVI.01336-18 (2018).
Chen, J. et al. Ephrin receptor A2 is a functional entry receptor for Epstein-Barr virus. Nat. Microbiol. 3, 172–180 (2018).
TerBush, A. A., Hafkamp, F., Lee, H. J. & Coscoy, L. A Kaposi’s sarcoma-associated herpesvirus infection mechanism is independent of integrins alpha3beta1, alphaVbeta3, and alphaVbeta5. J. Virol. https://doi.org/10.1128/JVI.00803-18 (2018).
Chen, J., Zhang, X., Schaller, S., Jardetzky, T. S. & Longnecker, R. Ephrin receptor A4 is a new Kaposi’s sarcoma-associated herpesvirus virus entry receptor. mBio https://doi.org/10.1128/mBio.02892-18 (2019).
Hahn, A. S. et al. The ephrin receptor tyrosine kinase A2 is a cellular receptor for Kaposi’s sarcoma-associated herpesvirus. Nat. Med. 18, 961–966 (2012).
Chesnokova, L. S. & Hutt-Fletcher, L. M. Fusion of Epstein-Barr virus with epithelial cells can be triggered by alphavbeta5 in addition to alphavbeta6 and alphavbeta8, and integrin binding triggers a conformational change in glycoproteins gHgL. J. Virol. 85, 13214–13223 (2011).
Li, Q., Turk, S. M. & Hutt-Fletcher, L. M. The Epstein-Barr virus (EBV) BZLF2 gene product associates with the gH and gL homologs of EBV and carries an epitope critical to infection of B cells but not of epithelial cells. J. Virol. 69, 3987–3994 (1995).
Yang, E., Arvin, A. M. & Oliver, S. L. Role for the alphaV integrin subunit in varicella-zoster virus-mediated fusion and infection. J. Virol. 90, 7567–7578 (2016).
Parry, C., Bell, S., Minson, T. & Browne, H. Herpes simplex virus type 1 glycoprotein H binds to alphavbeta3 integrins. J. Gen. Virol. 86, 7–10 (2005).
Gianni, T., Salvioli, S., Chesnokova, L. S., Hutt-Fletcher, L. M. & Campadelli-Fiume, G. alphavbeta6- and alphavbeta8-integrins serve as interchangeable receptors for HSV gH/gL to promote endocytosis and activation of membrane fusion. PLoS Pathog. 9, e1003806 (2013).
Chowdary, T. K. et al. Crystal structure of the conserved herpesvirus fusion regulator complex gH-gL. Nat. Strut Mol. Biol. 17, 882–888 (2010). Reports the crystal structure of HSV-2 gH–gL, exhibiting extensive interactions between gL and the N-terminal domain of gH.
Xing, Y. et al. A site of varicella-zoster virus vulnerability identified by structural studies of neutralizing antibodies bound to the glycoprotein complex gHgL. Proc. Natl Acad. Sci. USA 112, 6056–6061 (2015).
Backovic, M. et al. Structure of a core fragment of glycoprotein H from pseudorabies virus in complex with antibody. Proc. Natl Acad. Sci. USA 107, 22635–22640 (2010).
Matsuura, H., Kirschner, A. N., Longnecker, R. & Jardetzky, T. S. Crystal structure of the Epstein-Barr virus (EBV) glycoprotein H/glycoprotein L (gH/gL) complex. Proc. Natl Acad. Sci. USA 107, 22641–22646 (2010).
Connolly, S. A., Jackson, J. O., Jardetzky, T. S. & Longnecker, R. Fusing structure and function: a structural view of the herpesvirus entry machinery. Nat. Rev. Microbiol. 9, 369–381 (2011).
Gompels, U. A. et al. Characterization and sequence analyses of antibody-selected antigenic variants of herpes simplex virus show a conformationally complex epitope on glycoprotein H. J. Virol. 65, 2393–2401 (1991).
Ciferri, C. et al. Antigenic characterization of the HCMV gH/gL/gO and pentamer cell entry complexes reveals binding sites for potently neutralizing human antibodies. PLoS Pathog. 11, e1005230 (2015).
Sathiyamoorthy, K. et al. Inhibition of EBV-mediated membrane fusion by anti-gHgL antibodies. Proc. Natl Acad. Sci. USA https://doi.org/10.1073/pnas.1704661114 (2017).
Snijder, J. et al. An antibody targeting the fusion machinery neutralizes dual-tropic infection and defines a site of vulnerability on Epstein-Barr virus. Immunity 48, 799–811 e799 (2018).
Wilson, D. W., Davis-Poynter, N. & Minson, A. C. Mutations in the cytoplasmic tail of herpes simplex virus glycoprotein H suppress cell fusion by a syncytial strain. J. Virol. 68, 6985–6993 (1994).
Browne, H. M., Bruun, B. C. & Minson, A. C. Characterization of herpes simplex virus type 1 recombinants with mutations in the cytoplasmic tail of glycoprotein H. J. Gen. Virol. 77, 2569–2573 (1996).
Jackson, J. O., Lin, E., Spear, P. G. & Longnecker, R. Insertion mutations in herpes simplex virus 1 glycoprotein H reduce cell surface expression, slow the rate of cell fusion, or abrogate functions in cell fusion and viral entry. J. Virol. 84, 2038–2046 (2010).
Silverman, J. L. & Heldwein, E. E. Mutations in the cytoplasmic tail of herpes simplex virus 1 gH reduce the fusogenicity of gB in transfected cells. J. Virol. 87, 10139–10147 (2013).
Rogalin, H. B. & Heldwein, E. E. Interplay between the herpes simplex virus 1 gB cytodomain and the gH cytotail during cell-cell fusion. J. Virol. 89, 12262–12272 (2015).
Yang, E., Arvin, A. M. & Oliver, S. L. The cytoplasmic domain of varicella-zoster virus glycoprotein H regulates syncytia formation and skin pathogenesis. PLoS Pathog. 10, e1004173 (2014).
Vallbracht, M., Fuchs, W., Klupp, B. G. & Mettenleiter, T. C. Functional relevance of the transmembrane domain and cytoplasmic tail of the pseudorabies virus glycoprotein H for membrane fusion. J. Virol. 92, e00376–18 (2018).
Chen, J., Jardetzky, T. S. & Longnecker, R. The cytoplasmic tail domain of Epstein-Barr virus gH regulates membrane fusion activity through altering gH binding to gp42 and epithelial cell attachment. mBio https://doi.org/10.1128/mBio.01871-16 (2016).
Rowe, C. L., Connolly, S. A., Chen, J., Jardetzky, T. S. & Longnecker, R. A soluble form of Epstein-Barr virus gH/gL inhibits EBV-induced membrane fusion and does not function in fusion. Virology 436, 118–126 (2013).
Jones, N. A. & Geraghty, R. J. Fusion activity of lipid-anchored envelope glycoproteins of herpes simplex virus type 1. Virology 324, 213–228 (2004).
Cooper, R. S., Georgieva, E. R., Borbat, P. P., Freed, J. H. & Heldwein, E. E. Structural basis for membrane anchoring and fusion regulation of the herpes simplex virus fusogen gB. Nat. Struct. Mol. Biol. 25, 416–424 (2018). Reports the crystal structure of full-length HSV-1 gB, including the membrane-proximal, transmembrane, and cytoplasmic tail domains.
White, J. M., Delos, S. E., Brecher, M. & Schornberg, K. Structures and mechanisms of viral membrane fusion proteins: multiple variations on a common theme. Crit. Rev. Biochem. Mol. Bio 43, 189–219 (2008).
Heldwein, E. E. et al. Crystal structure of glycoprotein B from herpes simplex virus 1. Science 313, 217–220 (2006).
Vallbracht, M. et al. Structure-function dissection of the Pseudorabies virus glycoprotein B fusion loops. J. Virol. 92, e01203–01201 (2017).
Li, X. et al. Two classes of protective antibodies against Pseudorabies virus variant glycoprotein B: implications for vaccine design. PLoS Pathog. 13, e1006777 (2017).
Oliver, S. L. et al. A glycoprotein B-neutralizing antibody structure at 2.8 Å uncovers a critical domain for herpesvirus fusion initiation. Nat. Commun. 11, 1–15 (2020).
Chandramouli, S. et al. Structure of HCMV glycoprotein B in the postfusion conformation bound to a neutralizing human antibody. Nat. Commun. 6, 8176 (2015). Reports the crystal structure of the postfusion conformation of HCMV gB bound to a nAb.
Burke, H. G. & Heldwein, E. E. Crystal structure of the human cytomegalovirus glycoprotein B. PLoS Pathog. 11, e1005227 (2015). Reports the crystal structure of the postfusion conformation of HCMV gB.
Backovic, M., Longnecker, R. & Jardetzky, T. S. Structure of a trimeric variant of the Epstein-Barr virus glycoprotein B. Proc. Natl Acad. Sci. USA 106, 2880–2885 (2009).
Roche, S., Bressanelli, S., Rey, F. A. & Gaudin, Y. Crystal structure of the low-pH form of the vesicular stomatitis virus glycoprotein G. Science 313, 187–191 (2006).
Yang, F. et al. Structural analysis of rabies virus glycoprotein reveals pH-dependent conformational changes and interactions with a neutralizing antibody. Cell Host Microbe (2020).
Kadlec, J., Loureiro, S., Abrescia, N. G., Stuart, D. I. & Jones, I. M. The postfusion structure of baculovirus gp64 supports a unified view of viral fusion machines. Nat. Struct. Mol. Biol. 15, 1024–1030 (2008).
Peng, R. et al. Structures of human-infecting Thogotovirus fusogens support a common ancestor with insect baculovirus. Proc. Natl Acad. Sci. USA 114, E8905–E8912 (2017).
Backovic, M. & Jardetzky, T. S. Class III viral membrane fusion proteins. Curr. Opin. Struc Biol. 19, 189–196 (2009).
Bender, F. C. et al. Antigenic and mutational analyses of herpes simplex virus glycoprotein B reveal four functional regions. J. Virol. 81, 3827–3841 (2007).
Bootz, A. et al. Protective capacity of neutralizing and non-neutralizing antibodies against glycoprotein B of cytomegalovirus. PLoS Pathog. 13, e1006601 (2017).
Cairns, T. M. et al. Mechanism of neutralization of herpes simplex virus by antibodies directed at the fusion domain of glycoprotein B. J. Virol. 88, 2677–2689 (2014).
Lin, E. & Spear, P. G. Random linker-insertion mutagenesis to identify functional domains of herpes simplex virus type 1 glycoprotein B. Proc. Natl Acad. Sci. USA 104, 13140–13145 (2007).
Reimer, J. J., Backovic, M., Deshpande, C. G., Jardetzky, T. & Longnecker, R. Analysis of Epstein-Barr virus glycoprotein B functional domains via linker insertion mutagenesis. J. Virol. 83, 734–747 (2009).
Maurer, U. E. et al. The structure of herpesvirus fusion glycoprotein B-bilayer complex reveals the protein-membrane and lateral protein-protein interaction. Structure 21, 1396–1405 (2013).
Satoh, T. et al. PILRalpha is a herpes simplex virus-1 entry coreceptor that associates with glycoprotein B. Cell 132, 935–944 (2008).
Suenaga, T. et al. Myelin-associated glycoprotein mediates membrane fusion and entry of neurotropic herpesviruses. Proc. Natl Acad. Sci. USA 107, 866–871 (2010).
Arii, J. et al. Non-muscle myosin IIA is a functional entry receptor for herpes simplex virus-1. Nature 467, 859–862 (2010).
Roche, S., Rey, F. A., Gaudin, Y. & Bressanelli, S. Structure of the prefusion form of the vesicular stomatitis virus glycoprotein G. Science 315, 843–848 (2007).
Silverman, J. L., Sharma, S., Cairns, T. M. & Heldwein, E. E. Fusion-deficient insertion mutants of herpes simplex virus 1 glycoprotein B adopt the trimeric postfusion conformation. J. Virol. 84, 2001–2012 (2010).
Vitu, E., Sharma, S., Stampfer, S. D. & Heldwein, E. E. Extensive mutagenesis of the HSV-1 gB ectodomain reveals remarkable stability of its postfusion form. J. Mol. Biol. 425, 2056–2071 (2013).
Vollmer, B. et al. The pre-fusion structure of herpes simplex virus glycoprotein B. Sci. Adv. 6, eabc1726 (2020). EM reconstructions of a membrane-anchored HSV-1 gB mutant designed to trap the prefusion form reveal a compact structure at an overall resolution of 9 Å.
Falanga, A. et al. Biophysical characterization and membrane interaction of the two fusion loops of glycoprotein B from herpes simplex type I virus. PLoS ONE 7, e32186 (2012).
Oliver, S. L. et al. Mutagenesis of varicella-zoster virus glycoprotein B: putative fusion loop residues are essential for viral replication, and the furin cleavage motif contributes to pathogenesis in skin tissue in vivo. J. Virol. 83, 7495–7506 (2009).
Backovic, M., Jardetzky, T. S. & Longnecker, R. Hydrophobic residues that form putative fusion loops of Epstein-Barr virus glycoprotein B are critical for fusion activity. J. Virol. 81, 9596–9600 (2007).
Hannah, B. P. et al. Herpes simplex virus glycoprotein B associates with target membranes via its fusion loops. J. Virol. 83, 6825–6836 (2009).
Harrison, S. C. Viral membrane fusion. Virology 479–480, 498–507 (2015).
Melikyan, G. B. et al. Evidence that the transition of HIV-1 gp41 into a six-helix bundle, not the bundle configuration, induces membrane fusion. J. Cell Biol. 151, 413–423 (2000).
Connolly, S. A. & Longnecker, R. Residues within the C-terminal arm of the herpes simplex virus 1 glycoprotein B ectodomain contribute to its refolding during the fusion step of virus entry. J. Virol. 86, 6386–6393 (2012).
Fan, Q., Kopp, S. J., Connolly, S. A. & Longnecker, R. Structure-based mutations in the herpes simplex virus 1 glycoprotein b ectodomain arm impart a slow-entry phenotype. mBio https://doi.org/10.1128/mBio.00614-17 (2017).
Waning, D. L., Russell, C. J., Jardetzky, T. S. & Lamb, R. A. Activation of a paramyxovirus fusion protein is modulated by inside-out signaling from the cytoplasmic tail. Proc. Natl Acad. Sci. USA 101, 9217–9222 (2004).
Wyss, S. et al. Regulation of human immunodeficiency virus type 1 envelope glycoprotein fusion by a membrane-interactive domain on the gp41 cytoplasmic tail. J. Virol. 79, 12231–12241 (2005).
Garcia, N. J., Chen, J. & Longnecker, R. Modulation of Epstein-Barr virus glycoprotein B (gB) fusion activity by the gB cytoplasmic tail domain. mBio 4, e00571–12 (2013).
Nixdorf, R., Klupp, B. G., Karger, A. & Mettenleiter, T. C. Effects of truncation of the carboxy terminus of pseudorabies virus glycoprotein B on infectivity. J. Virol. 74, 7137–7145 (2000).
Fan, Z. et al. Truncation of herpes simplex virus type 2 glycoprotein B increases its cell surface expression and activity in cell-cell fusion, but these properties are unrelated. J. Virol. 76, 9271–9283 (2002).
Muggeridge, M. I., Grantham, M. L. & Johnson, F. B. Identification of syncytial mutations in a clinical isolate of herpes simplex virus 2. Virology 328, 244–253 (2004).
Silverman, J. L., Greene, N. G., King, D. S. & Heldwein, E. E. Membrane requirement for folding of the herpes simplex virus 1 gB cytodomain suggests a unique mechanism of fusion regulation. J. Virol. 86, 8171–8184 (2012).
Oliver, S. L. et al. An immunoreceptor tyrosine-based inhibition motif in varicella-zoster virus glycoprotein B regulates cell fusion and skin pathogenesis. Proc. Natl Acad. Sci. USA 110, 1911–1916 (2013).
Cooper, R. S. & Heldwein, E. E. Herpesvirus gB: a finely tuned fusion machine. Viruses 7, 6552–6569 (2015).
Gallagher, J. R. et al. Functional fluorescent protein insertions in herpes simplex virus gB report on gB conformation before and after execution of membrane fusion. PLoS Pathog. 10, e1004373 (2014).
Zeev-Ben-Mordehai, T. et al. Two distinct trimeric conformations of natively membrane-anchored full-length herpes simplex virus 1 glycoprotein B. Proc. Natl Acad. Sci. USA 113, 4176–4181 (2016).
Fontana, J. et al. The fusion loops of the initial prefusion conformation of herpes simplex virus 1 fusion protein point toward the membrane. mBio https://doi.org/10.1128/mBio.01268-17 (2017).
Si, Z. et al. Different functional states of fusion protein gB revealed on human cytomegalovirus by cryo electron tomography with Volta phase plate. PLoS Pathog. 14, e1007452 (2018).
Handler, C. G., Cohen, G. H. & Eisenberg, R. J. Cross-linking of glycoprotein oligomers during herpes simplex virus type 1 entry. J. Virol. 70, 6076–6082 (1996).
Gianni, T., Amasio, M. & Campadelli-Fiume, G. Herpes simplex virus gD forms distinct complexes with fusion executors gB and gH/gL in part through the C-terminal profusion domain. J. Biol. Chem. 284, 17370–17382 (2009).
Perez-Romero, P., Perez, A., Capul, A., Montgomery, R. & Fuller, A. O. Herpes simplex virus entry mediator associates in infected cells in a complex with viral proteins gD and at least gH. J. Virol. 79, 4540–4544 (2005).
Avitabile, E., Forghieri, C. & Campadelli-Fiume, G. Complexes between herpes simplex virus glycoproteins gD, gB, and gH detected in cells by complementation of split enhanced green fluorescent protein. J. Virol. 81, 11532–11537 (2007).
Atanasiu, D. et al. Bimolecular complementation reveals that glycoproteins gB and gH/gL of herpes simplex virus interact with each other during cell fusion. Proc. Natl Acad. Sci. USA 104, 18718–18723 (2007).
Fan, Q., Longnecker, R. & Connolly, S. A. Substitution of herpes simplex virus 1 entry glycoproteins with those of saimiriine herpesvirus 1 reveals a gD-gH/gL functional interaction and a region within the gD profusion domain that is critical for fusion. J. Virol. 88, 6470–6482 (2014).
Fan, Q., Longnecker, R. & Connolly, S. A. A functional interaction between herpes simplex virus 1 glycoprotein gH/gL domains I and II and gD is defined by using alphaherpesvirus gH and gL chimeras. J. Virol. 89, 7159–7169 (2015).
Atanasiu, D. et al. Regulation of herpes simplex virus gB-induced cell-cell fusion by mutant forms of gH/gL in the absence of gD and cellular receptors. mBio https://doi.org/10.1128/mBio.00046-13 (2013).
Cairns, T. M. et al. Surface plasmon resonance reveals direct binding of herpes simplex virus glycoproteins gH/gL to gD and Locates a gH/gL binding site on gD. J. Virol. https://doi.org/10.1128/JVI.00289-19 (2019). Demonstrates direct interaction between purified forms of the HSV-2 gD and gH–gL ectodomains.
Atanasiu, D. et al. Bimolecular complementation defines functional regions of Herpes simplex virus gB that are involved with gH/gL as a necessary step leading to cell fusion. J. Virol. 84, 3825–3834 (2010).
Vanarsdall, A. L., Ryckman, B. J., Chase, M. C. & Johnson, D. C. Human cytomegalovirus glycoproteins gB and gH/gL mediate epithelial cell-cell fusion when expressed in cis or in trans. J. Virol. 82, 11837–11850 (2008).
Oxman, M. N. et al. A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults. N. Engl. J. Med. 352, 2271–2284 (2005).
Cunningham, A. L. et al. Efficacy of the herpes zoster subunit vaccine in adults 70 years of age or older. N. Engl. J. Med. 375, 1019–1032 (2016).
This work was supported by grants AI-137267 and AI-148478 from the US National Institute of Allergy and Infectious Diseases of the National Institutes of Health. All crystal structures in this Review were rendered with MacPyMOL.
The authors declare no competing interests.
Peer review information
Nature Reviews Microbiology thanks A. Carfi, K. Grünewald, A. Nicola, L. Perez, B. Vollmer and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
RCSB Protein Data Bank: https://www.rcsb.org/
- Enveloped viruses
Viruses with an outer layer consisting of a lipid bilayer, in which the viral glycoproteins responsible for mediating virus entry into cells are embedded.
- Conformational changes
Changes in protein structure made possible by the intrinsic flexibility of the protein that can be triggered by environmental factors, such as binding to a receptor or another glycoprotein.
- Entry receptors
Molecules present in host cells that bind directly to viruses and mediate virus entry into the cell.
- Cell tropism
The specific cell types that support the replication of different viruses.
- Crystal structures
Structural models based on X-ray diffraction of a crystal that often permit atomic resolution for protein structures.
- Neutralizing monoclonal antibodies
(nAbs). Antibodies that bind to a virus particle and prevent infection, typically by preventing virus entry into the cell.
- Fusion loops
Short stretches of hydrophobic residues within a fusion protein that insert themselves into the host cell membrane during the fusion event.
- Cryo-electron tomography
(cryo-ET). Method to produce high-resolution 3D models of molecules held at cryogenic temperature by reconstructing a series of 2D electron microscopy images taken from multiple angles.
About this article
Cite this article
Connolly, S.A., Jardetzky, T.S. & Longnecker, R. The structural basis of herpesvirus entry. Nat Rev Microbiol (2020). https://doi.org/10.1038/s41579-020-00448-w