scholarly journals Engineered Disulfide Bonds in Herpes Simplex Virus Type 1 gD Separate Receptor Binding from Fusion Initiation and Viral Entry

2007 ◽  
Vol 82 (2) ◽  
pp. 700-709 ◽  
Author(s):  
Eric Lazear ◽  
Andrea Carfi ◽  
J. Charles Whitbeck ◽  
Tina M. Cairns ◽  
Claude Krummenacher ◽  
...  
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Cell Fusion ◽  
Receptor Binding ◽  
Disulfide Bond ◽  
Viral Entry ◽  
Disulfide Bonds ◽  
C Terminus ◽  
Simplex Virus ◽  
Cell Cell

ABSTRACT Glycoprotein D (gD) is the receptor binding protein of herpes simplex virus (HSV) and binds to at least two distinct protein receptors, herpesvirus entry mediator (HVEM) and nectin-1. While both receptor binding regions are found within the first 234 amino acids, a crystal structure shows that the C terminus of the gD ectodomain normally occludes the receptor binding sites. Receptor binding must therefore displace the C terminus, and this conformational change is postulated to be required for inducing fusion via gB and gH/gL. When cysteine residues are introduced at positions 37 and 302 of gD, a disulfide bond is formed that stabilizes the C terminus and prevents binding to either receptor. We speculated that if disulfide bonds were engineered further upstream, receptor binding might be separated from the induction of fusion. To test this, we made five additional double cysteine mutants, each potentially introducing a disulfide bond between the ectodomain C terminus and the core of the gD ectodomain. The two mutants predicted to impose the greatest constraint were unable to bind receptors or mediate cell-cell fusion. However, the three mutants with the most flexible C terminus bound well to both HVEM and nectin-1. Two of these mutants were impaired in cell-cell fusion and null-virus complementation. Importantly, a third mutant in this group was nonfunctional in both assays. This mutant clearly separates the role of gD in triggering fusion from its role in receptor binding. Based upon the properties of the panel of mutants we conclude that fusion requires greater flexibility of the gD ectodomain C terminus than does receptor binding.

scholarly journals Displacement of the C Terminus of Herpes Simplex Virus gD Is Sufficient To Expose the Fusion-Activating Interfaces on gD

2013 ◽  
Vol 87 (23) ◽  
pp. 12656-12666 ◽  
Author(s):  
John R. Gallagher ◽  
Wan Ting Saw ◽  
Doina Atanasiu ◽  
Huan Lou ◽  
Roselyn J. Eisenberg ◽  
...  
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Membrane Fusion ◽  
Receptor Binding ◽  
Viral Entry ◽  
Tertiary Structure ◽  
Host Cells ◽  
Binding Interface ◽  
C Terminus ◽  
Simplex Virus

Viral entry by herpes simplex virus (HSV) is executed and tightly regulated by four glycoproteins. While several viral glycoproteins can mediate viral adhesion to host cells, only binding of gD to cellular receptor can activate core fusion proteins gB and gH/gL to execute membrane fusion and viral entry. Atomic structures of gD bound to receptor indicate that the C terminus of the gD ectodomain must be displaced before receptor can bind to gD, but it is unclear which conformational changes in gD activate membrane fusion. We rationally designed mutations in gD to displace the C terminus and observe if fusion could be activated without receptor binding. Using a cell-based fusion assay, we found that gD V231W induced cell-cell fusion in the absence of receptor. Using recombinant gD V231W protein, we observed binding to conformationally sensitive antibodies or HSV receptor and concluded that there were changes proximal to the receptor binding interface, while the tertiary structure of gD V231W was similar to that of wild-type gD. We used a biosensor to analyze the kinetics of receptor binding and the extent to which the C terminus blocks binding to receptor. We found that the C terminus of gD V231W was enriched in the open or displaced conformation, indicating a mechanism for its function. We conclude that gD V231W triggers fusion through displacement of its C terminus and that this motion is indicative of how gD links receptor binding to exposure of interfaces on gD that activate fusion via gH/gL and gB.

scholarly journals HveA (Herpesvirus Entry Mediator A), a Coreceptor for Herpes Simplex Virus Entry, also Participates in Virus-Induced Cell Fusion

1998 ◽  
Vol 72 (7) ◽  
pp. 5802-5810 ◽  
Author(s):  
Tracy Terry-Allison ◽  
Rebecca I. Montgomery ◽  
J. Charles Whitbeck ◽  
Ruliang Xu ◽  
Gary H. Cohen ◽  
...  
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Cell Fusion ◽  
Viral Entry ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Simplex Virus ◽  
Herpesvirus Entry Mediator ◽  
Hsv 1 ◽  
Cell Cell

ABSTRACT The purpose of this study was to determine whether a cell surface protein that can serve as coreceptor for herpes simplex virus type 1 (HSV-1) entry, herpesvirus entry mediator (previously designated HVEM but renamed HveA), also mediates HSV-1-induced cell-cell fusion. We found that transfection of DNA from KOS-804, a previously described HSV-1 syncytial (Syn) strain whose Syn mutation was mapped to an amino acid substitution in gK, induced numerous large syncytia on HveA-expressing Chinese hamster ovary cells (CHO-HVEM12) but not on control cells (CHO-C8). Antibodies specific for gD as well as for HveA were effective inhibitors of KOS-804-induced fusion, consistent with previously described direct interactions between gD and HveA. Since mutations in gD determine the ability of HSV-1 to utilize HveA for entry, we examined whether the form of virally expressed gD also influenced the ability of HveA to mediate fusion. We produced a recombinant virus carrying the KOS-804 Syn mutation and the KOS-Rid1 gD mutation, which significantly reduces viral entry via HveA, and designated it KOS-SR1. KOS-SR1 DNA had a markedly reduced ability to induce syncytia on CHO-HVEM12 cells and a somewhat enhanced ability to induce syncytia on CHO-C8 cells. These results support previous findings concerning the relative abilities of KOS and KOS-Rid1 to infect CHO-HVEM12 and CHO-C8 cells. Thus, HveA mediates cell-cell fusion as well as viral entry and both activities of HveA are contingent upon the form of gD expressed by the virus.

scholarly journals Cascade of Events Governing Cell-Cell Fusion Induced by Herpes Simplex Virus Glycoproteins gD, gH/gL, and gB

2010 ◽  
Vol 84 (23) ◽  
pp. 12292-12299 ◽  
Author(s):  
Doina Atanasiu ◽  
Wan Ting Saw ◽  
Gary H. Cohen ◽  
Roselyn J. Eisenberg
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Fusion Protein ◽  
Cell Fusion ◽  
Receptor Binding ◽  
Conformational Changes ◽  
Structural Level ◽  
Viral Fusion Protein ◽  
Simplex Virus ◽  
Cell Cell

ABSTRACT Herpesviruses minimally require the envelope proteins gB and gH/gL for virus entry and cell-cell fusion; herpes simplex virus (HSV) additionally requires the receptor-binding protein gD. Although gB is a class III fusion protein, gH/gL does not resemble any documented viral fusion protein at a structural level. Based on those data, we proposed that gH/gL does not function as a cofusogen with gB but instead regulates the fusogenic activity of gB. Here, we present data to support that hypothesis. First, receptor-positive B78H1-C10 cells expressing gH/gL fused with receptor-negative B78H1 cells expressing gB and gD (fusion in trans). Second, fusion occurred when gH/gL-expressing C10 cells preexposed to soluble gD were subsequently cocultured with gB-expressing B78 cells. In contrast, prior exposure of gB-expressing C10 cells to soluble gD did not promote subsequent fusion with gH/gL-expressing B78 cells. These data suggest that fusion involves activation of gH/gL by receptor-bound gD. Most importantly, soluble gH/gL triggered a low level of fusion of C10 cells expressing gD and gB; a much higher level was achieved when gB-expressing C10 cells were exposed to a combination of soluble gH/gL and gD. These data clearly show that gB acts as the HSV fusogen following activation by gD and gH/gL. We suggest the following steps leading to fusion: (i) conformational changes to gD upon receptor binding, (ii) alteration of gH/gL by receptor-activated gD, and (iii) upregulation of the fusogenic potential of gB following its interaction with activated gH/gL. The third step may be common to other herpesviruses.

scholarly journals Contribution of Endocytic Motifs in the Cytoplasmic Tail of Herpes Simplex Virus Type 1 Glycoprotein B to Virus Replication and Cell-Cell Fusion

2007 ◽  
Vol 81 (24) ◽  
pp. 13889-13903 ◽  
Author(s):  
Igor Beitia Ortiz de Zarate ◽  
Lilia Cantero-Aguilar ◽  
Magalie Longo ◽  
Clarisse Berlioz-Torrent ◽  
Flore Rozenberg
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Cell Surface ◽  
Cell Fusion ◽  
Virus Replication ◽  
Herpes Simplex Virus Type ◽  
Wild Type ◽  
Simplex Virus ◽  
Cell Cell

ABSTRACT The use of endocytic pathways by viral glycoproteins is thought to play various functions during viral infection. We previously showed in transfection assays that herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is transported from the cell surface back to the trans-Golgi network (TGN) and that two motifs of gB cytoplasmic tail, YTQV and LL, function distinctly in this process. To investigate the role of each of these gB trafficking signals in HSV-1 infection, we constructed recombinant viruses in which each motif was rendered nonfunctional by alanine mutagenesis. In infected cells, wild-type gB was internalized from the cell surface and concentrated in the TGN. Disruption of YTQV abolished internalization of gB during infection, whereas disruption of LL induced accumulation of internalized gB in early recycling endosomes and impaired its return to the TGN. The growth of both recombinants was moderately diminished. Moreover, the fusion phenotype of cells infected with the gB recombinants differed from that of cells infected with the wild-type virus. Cells infected with the YTQV-mutated virus displayed reduced cell-cell fusion, whereas giant syncytia were observed in cells infected with the LL-mutated virus. Furthermore, blocking gB internalization or impairing gB recycling to the cell surface, using drugs or a transdominant negative form of Rab11, significantly reduced cell-cell fusion. These results favor a role for endocytosis in virus replication and suggest that gB intracellular trafficking is involved in the regulation of cell-cell fusion.

scholarly journals The Domains of Glycoprotein D Required To Block Apoptosis Induced by Herpes Simplex Virus 1 Are Largely Distinct from Those Involved in Cell-Cell Fusion and Binding to Nectin1

2003 ◽  
Vol 77 (6) ◽  
pp. 3759-3767 ◽  
Author(s):  
Guoying Zhou ◽  
Elisa Avitabile ◽  
Gabriella Campadelli-Fiume ◽  
Bernard Roizman
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Cell Fusion ◽  
Ectopic Expression ◽  
Full Length ◽  
Glycoprotein D ◽  
Herpes Simplex Virus 1 ◽  
Mannose 6 Phosphate ◽  
Simplex Virus ◽  
Cell Cell

ABSTRACT Glycoprotein D (gD) interacts with two alternative protein receptors, nectin1 and HveA, to mediate herpes simplex virus (HSV) entry into cells. Fusion of the envelope with the plasma membrane requires, in addition to gD, glycoproteins gB, gH, and gL. Coexpression of the four glycoproteins (gD, gB, gH, and gL) promotes cell-cell fusion. gD delivered in trans is also capable of blocking the apoptosis induced by gD deletion viruses grown either in noncomplementing cells (gD−/−) or in complementing cells (gD−/+). While ectopic expression of cation-independent mannose-6 phosphate receptor blocks apoptosis induced by both stocks, other requirements differ. Thus, apoptosis induced by gD−/− virus is blocked by full-length gD (or two gD fragments reconstituting a full-length molecule), whereas ectopic expression of the gD ectodomain is sufficient to block apoptosis induced by gD−/+ virus. In this report we took advantage of a set of gD insertion-deletion mutants to map the domains of gD required to block apoptosis by gD−/− and gD−/+ viruses and those involved in cell-cell fusion. The mutations that resulted in failure to block apoptosis were the same for gD−/− and gD−/+ viruses and were located in three sites, one within the immunoglobulin-type core region (residues 125, 126, and 151), one in the upstream connector region (residues 34 and 43), and one in the C-terminal portion of the ectodomain (residue 277). A mutant that carried amino acid substitutions at the three glycosylation sites failed to block apoptosis but behaved like wild-type gD in all other assays. The mutations that inhibited polykaryocyte formation were located in the upstream connector region (residues 34 and 43), at the α1 helix (residue 77), in the immunoglobulin core and downstream regions (residue 151 and 187), and at the α3 helix (residues 243 and 246). Binding of soluble nectin1-Fc to cells expressing the mutant gDs was generally affected by the same mutations that affected fusion, with one notable exception (Δ277-310), which affected fusion without hampering nectin1 binding. This deletion likely identifies a region of gD involved in fusion activity at a post-nectin1-binding step. We conclude that whereas mutations that affected all functions (e.g., upstream connector region and residue 151) may be detrimental to overall gD structure, the mutations that affect specific activities identify domains of gD involved in the interactions with entry receptors and fusogenic glycoproteins and with cellular proteins required to block apoptosis. The evidence that glycosylation of gD is required for blocking apoptosis supports the conclusion that the interacting protein is the mannose-6 phosphate receptor.

scholarly journals Insertional Mutations in Herpes Simplex Virus Type 1 gL Identify Functional Domains for Association with gH and for Membrane Fusion

2009 ◽  
Vol 83 (22) ◽  
pp. 11607-11615 ◽  
Author(s):  
Qing Fan ◽  
Erick Lin ◽  
Patricia G. Spear
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Cell Surface ◽  
Membrane Fusion ◽  
Cell Fusion ◽  
Viral Entry ◽  
Cell Surface Receptor ◽  
Cell Surface Expression ◽  
Conserved Domain ◽  
Simplex Virus

ABSTRACT Glycoprotein L (gL) is one of four glycoproteins required for the entry of herpes simplex virus (HSV) into cells and for virus-induced cell fusion. This glycoprotein oligomerizes with gH to form a membrane-bound heterodimer but can be secreted when expressed without gH. Twelve unique gL linker-insertion mutants were generated to identify regions critical for gH binding and gH/gL processing and regions essential for cell fusion and viral entry. All gL mutants were detected on the cell surface in the absence of gH, suggesting incomplete cleavage of the signal peptide or the presence of a cell surface receptor for secreted gL. Coexpression with gH enhanced the levels of cell surface gL detected by antibodies for all gL mutants except those that were defective in their interactions with gH. Two insertions into a conserved region of gL abrogated the binding of gL to gH and prevented gH expression on the cell surface. Three other insertions reduced the cell surface expression of gH and/or altered the properties of gH/gL heterodimers. Altered or absent interaction of gL with gH was correlated with reduced or absent cell fusion activity and impaired complementation of virion infectivity. These results identify a conserved domain of gL that is critical for its binding to gH and two noncontiguous regions of gL, one of which contains the conserved domain, that are critical for the gH/gL complex to perform its role in membrane fusion.

scholarly journals Using a split luciferase assay (SLA) to measure the kinetics of cell–cell fusion mediated by herpes simplex virus glycoproteins

Methods ◽  
2015 ◽  
Vol 90 ◽  
pp. 68-75 ◽  
Author(s):  
Wan Ting Saw ◽  
Zene Matsuda ◽  
Roselyn J. Eisenberg ◽  
Gary H. Cohen ◽  
Doina Atanasiu
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Cell Fusion ◽  
Luciferase Assay ◽  
Simplex Virus ◽  
Kinetics Of ◽  
Split Luciferase ◽  
Cell Cell

scholarly journals Structure-Function Analysis of Herpes Simplex Virus Type 1 gD and gH-gL: Clues from gDgH Chimeras

2003 ◽  
Vol 77 (12) ◽  
pp. 6731-6742 ◽  
Author(s):  
Tina M. Cairns ◽  
Richard S. B. Milne ◽  
Manuel Ponce-de-Leon ◽  
Deanna K. Tobin ◽  
Gary H. Cohen ◽  
...  
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Cell Surface ◽  
Cell Fusion ◽  
Virus Type ◽  
Herpes Simplex Virus Type ◽  
Simplex Virus ◽  
Hsv 1 ◽  
Cell Cell

ABSTRACT In alphaherpesviruses, glycoprotein B (gB), gD, gH, and gL are essential for virus entry. A replication-competent gL-null pseudorabies virus (PrV) (B. G. Klupp and T. C. Mettenleiter, J. Virol. 73:3014-3022, 1999) was shown to express a gDgH hybrid protein that could replace gD, gH, and gL in cell-cell fusion and null virus complementation assays. To study this phenomenon in herpes simplex virus type 1 (HSV-1), we constructed four gDgH chimeras, joining the first 308 gD amino acids to various gH N-terminal truncations. The chimeras were named for the first amino acid of gH at which each was truncated: 22, 259, 388, and 432. All chimeras were immunoprecipitated with both gD and gH antibodies to conformational epitopes. Normally, transport of gH to the cell surface requires gH-gL complex formation. Chimera 22 contains full-length gH fused to gD308. Unlike PrV gDgH, chimera 22 required gL for transport to the surface of transfected Vero cells. Interestingly, although chimera 259 failed to reach the cell surface, chimeras 388 and 432 exhibited gL-independent transport. To examine gD and gH domain function, each chimera was tested in cell-cell fusion and null virus complementation assays. Unlike PrV gDgH, none of the HSV-1 chimeras substituted for gL for fusion. Only chimera 22 was able to replace gH for fusion and could also replace either gH or gD in the complementation assay. Surprisingly, this chimera performed very poorly as a substitute for gD in the fusion assay despite its ability to complement gD-null virus and bind HSV entry receptors (HveA and nectin-1). Chimeras 388 and 432, which contain the same portion of gD as that in chimera 22, substituted for gD for fusion at 25 to 50% of wild-type levels. However, these chimeras functioned poorly in gD-null virus complementation assays. The results highlight the fact that these two functional assays are measuring two related but distinct processes.

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