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Regulation of herpes simplex virus gB-induced cell-cell fusion by mutant forms of gH/gL in the absence of gD and cellular receptors.

Atanasiu D, Cairns TM, Whitbeck JC, Saw WT, Rao S, Eisenberg RJ, Cohen GH - MBio (2013)

Bottom Line: Unexplainably, monoclonal antibodies (MAbs) with virus-neutralizing activity map to these residues.The absence of any of these proteins abolishes the entry process.Our study supports the concept that gB is the HSV fusogen and its activity is regulated by gH/gL.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

ABSTRACT

Unlabelled: Herpesvirus entry requires the viral glycoprotein triad of gB and gH/gL to carry out fusion between the virion envelope and a cellular membrane in order to release the nucleocapsid into the target cell. Herpes simplex virus (HSV) also requires glycoprotein gD to initiate the fusion cascade by binding a cell receptor such as nectin 1 or herpesvirus entry mediator (HVEM). While the structure of gB is that of a class III fusion protein, gH/gL has no features that resemble other viral fusion proteins. Instead, it is suggested that gH/gL acts as a regulator of gB. The crystal structure of HSV-2 gH/gL was obtained with a functional protein that had a deletion of 28 residues at the gH N terminus (gHΔ48/gL). Unexplainably, monoclonal antibodies (MAbs) with virus-neutralizing activity map to these residues. To reconcile these two disparate observations, we studied the ability of gHΔ48/gL to regulate fusion. Here, we show that the protein induces low (constitutive) levels of fusion by gB in the absence of gD and/or receptor. However, when gD and receptor are present, this mutant functions as well as does wild-type (wt) gH/gL for fusion. We propose that gHΔ48/gL has an intermediate structure on the pathway leading to full regulatory activation. We suggest that a key step in the pathway of fusion is the conversion of gH/gL to an activated state by receptor-bound gD; this activated gH/gL resembles gHΔ48/gL.

Importance: Herpes simplex viruses (HSVs) cause many human diseases, from mild cold sores to lethal neonatal herpes. As an enveloped virus, HSV must fuse its membrane with a host membrane in order for replication to take place. The virus uses four glycoproteins for this process, gD, gB, and gH/gL, and either of two cell receptors, herpesvirus entry mediator (HVEM) and nectin 1. Although the virus can enter the cell by direct fusion at the plasma membrane or via endocytosis, the same four glycoproteins are involved. The absence of any of these proteins abolishes the entry process. Here, we show that a mutant form of gH/gL, gHΔ48/gL, can induce fusion of gB-expressing cells in the absence of gD and a gD receptor. Our study supports the concept that gB is the HSV fusogen and its activity is regulated by gH/gL.

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Crystal structure and diagrams of constructs used. (A) Crystal structure of gHΔ48/gL. Domain organization as published. Residues 19 to 47 of gH, which are missing from gHΔ48/gL, and the unresolved gL residues 204 to 224 are shown as dashed lines (green and aqua, respectively). (B) Diagrams of gH and gL constructs used in this study. The epitopes of monoclonal antibodies used are indicated in the same color scheme as in panel A. For gH, CHL2 (white; MAR 116), CHL25 (pink; 73 to 92), 52S (dark blue; MAR 536), and LP11 (red; MARs 86, 168, and 329). For gL, CHL34 (purple; 146 to 165), CΔ48L3 (black; 173 to 183), CHL26 (brown; 195 to 208), and CHL18 (aqua; 209 to 219).
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fig1: Crystal structure and diagrams of constructs used. (A) Crystal structure of gHΔ48/gL. Domain organization as published. Residues 19 to 47 of gH, which are missing from gHΔ48/gL, and the unresolved gL residues 204 to 224 are shown as dashed lines (green and aqua, respectively). (B) Diagrams of gH and gL constructs used in this study. The epitopes of monoclonal antibodies used are indicated in the same color scheme as in panel A. For gH, CHL2 (white; MAR 116), CHL25 (pink; 73 to 92), 52S (dark blue; MAR 536), and LP11 (red; MARs 86, 168, and 329). For gL, CHL34 (purple; 146 to 165), CΔ48L3 (black; 173 to 183), CHL26 (brown; 195 to 208), and CHL18 (aqua; 209 to 219).

Mentions: This report describes newly discovered properties of two previously derived type 2 gH mutants (gH2Δ29 and gH2Δ48) and a type 1 gH deletion, gH1Δ48 (Fig 1) (23). All mutants retain the gH signal sequence and lack either the first 10 amino acids (residues 19 to 28 for gH2Δ29) or the first 29 amino acids (residues 19 to 47 for gH1Δ48 and gH2Δ48) of mature gH (Fig. 1). However, the ability of these mutants to promote cell-cell fusion or virus entry (23) contrasted with the fact that epitopes of two virus-neutralizing gH2-specific monoclonal antibodies (MAbs), CHL17 and CHL32, map within the deleted residues of the gH2 N terminus (24). This apparent disparity warranted a closer look at the gH2 N terminus and its role in gH2/gL2 function.


Regulation of herpes simplex virus gB-induced cell-cell fusion by mutant forms of gH/gL in the absence of gD and cellular receptors.

Atanasiu D, Cairns TM, Whitbeck JC, Saw WT, Rao S, Eisenberg RJ, Cohen GH - MBio (2013)

Crystal structure and diagrams of constructs used. (A) Crystal structure of gHΔ48/gL. Domain organization as published. Residues 19 to 47 of gH, which are missing from gHΔ48/gL, and the unresolved gL residues 204 to 224 are shown as dashed lines (green and aqua, respectively). (B) Diagrams of gH and gL constructs used in this study. The epitopes of monoclonal antibodies used are indicated in the same color scheme as in panel A. For gH, CHL2 (white; MAR 116), CHL25 (pink; 73 to 92), 52S (dark blue; MAR 536), and LP11 (red; MARs 86, 168, and 329). For gL, CHL34 (purple; 146 to 165), CΔ48L3 (black; 173 to 183), CHL26 (brown; 195 to 208), and CHL18 (aqua; 209 to 219).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585445&req=5

fig1: Crystal structure and diagrams of constructs used. (A) Crystal structure of gHΔ48/gL. Domain organization as published. Residues 19 to 47 of gH, which are missing from gHΔ48/gL, and the unresolved gL residues 204 to 224 are shown as dashed lines (green and aqua, respectively). (B) Diagrams of gH and gL constructs used in this study. The epitopes of monoclonal antibodies used are indicated in the same color scheme as in panel A. For gH, CHL2 (white; MAR 116), CHL25 (pink; 73 to 92), 52S (dark blue; MAR 536), and LP11 (red; MARs 86, 168, and 329). For gL, CHL34 (purple; 146 to 165), CΔ48L3 (black; 173 to 183), CHL26 (brown; 195 to 208), and CHL18 (aqua; 209 to 219).
Mentions: This report describes newly discovered properties of two previously derived type 2 gH mutants (gH2Δ29 and gH2Δ48) and a type 1 gH deletion, gH1Δ48 (Fig 1) (23). All mutants retain the gH signal sequence and lack either the first 10 amino acids (residues 19 to 28 for gH2Δ29) or the first 29 amino acids (residues 19 to 47 for gH1Δ48 and gH2Δ48) of mature gH (Fig. 1). However, the ability of these mutants to promote cell-cell fusion or virus entry (23) contrasted with the fact that epitopes of two virus-neutralizing gH2-specific monoclonal antibodies (MAbs), CHL17 and CHL32, map within the deleted residues of the gH2 N terminus (24). This apparent disparity warranted a closer look at the gH2 N terminus and its role in gH2/gL2 function.

Bottom Line: Unexplainably, monoclonal antibodies (MAbs) with virus-neutralizing activity map to these residues.The absence of any of these proteins abolishes the entry process.Our study supports the concept that gB is the HSV fusogen and its activity is regulated by gH/gL.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

ABSTRACT

Unlabelled: Herpesvirus entry requires the viral glycoprotein triad of gB and gH/gL to carry out fusion between the virion envelope and a cellular membrane in order to release the nucleocapsid into the target cell. Herpes simplex virus (HSV) also requires glycoprotein gD to initiate the fusion cascade by binding a cell receptor such as nectin 1 or herpesvirus entry mediator (HVEM). While the structure of gB is that of a class III fusion protein, gH/gL has no features that resemble other viral fusion proteins. Instead, it is suggested that gH/gL acts as a regulator of gB. The crystal structure of HSV-2 gH/gL was obtained with a functional protein that had a deletion of 28 residues at the gH N terminus (gHΔ48/gL). Unexplainably, monoclonal antibodies (MAbs) with virus-neutralizing activity map to these residues. To reconcile these two disparate observations, we studied the ability of gHΔ48/gL to regulate fusion. Here, we show that the protein induces low (constitutive) levels of fusion by gB in the absence of gD and/or receptor. However, when gD and receptor are present, this mutant functions as well as does wild-type (wt) gH/gL for fusion. We propose that gHΔ48/gL has an intermediate structure on the pathway leading to full regulatory activation. We suggest that a key step in the pathway of fusion is the conversion of gH/gL to an activated state by receptor-bound gD; this activated gH/gL resembles gHΔ48/gL.

Importance: Herpes simplex viruses (HSVs) cause many human diseases, from mild cold sores to lethal neonatal herpes. As an enveloped virus, HSV must fuse its membrane with a host membrane in order for replication to take place. The virus uses four glycoproteins for this process, gD, gB, and gH/gL, and either of two cell receptors, herpesvirus entry mediator (HVEM) and nectin 1. Although the virus can enter the cell by direct fusion at the plasma membrane or via endocytosis, the same four glycoproteins are involved. The absence of any of these proteins abolishes the entry process. Here, we show that a mutant form of gH/gL, gHΔ48/gL, can induce fusion of gB-expressing cells in the absence of gD and a gD receptor. Our study supports the concept that gB is the HSV fusogen and its activity is regulated by gH/gL.

Show MeSH
Related in: MedlinePlus