Abstract
Members of the Herpesviridae, including the medically important alphaherpesvirus varicella-zoster virus (VZV), induce fusion of the virion envelope with cell membranes during entry, and between cells to form polykaryocytes in infected tissues. The conserved glycoproteins, gB, gH and gL, are the core functional proteins of the herpesvirus fusion complex. gB serves as the primary fusogen via its fusion loops, but functions for the remaining gB domains remain unexplained. As a pathway for biological discovery of domain function, our approach used structure-based analysis of the viral fusogen together with a neutralizing antibody. We report here a 2.8 Å cryogenic-electron microscopy structure of native gB recovered from VZV-infected cells, in complex with a human monoclonal antibody, 93k. This high-resolution structure guided targeted mutagenesis at the gB-93k interface, providing compelling evidence that a domain spatially distant from the gB fusion loops is critical for herpesvirus fusion, revealing a potential new target for antiviral therapies.
Highlights
Members of the Herpesviridae, including the medically important alphaherpesvirus varicellazoster virus (VZV), induce fusion of the virion envelope with cell membranes during entry, and between cells to form polykaryocytes in infected tissues
The neutralization of cell-free VZV and the fusion inhibition properties of Monoclonal antibodies (mAbs) 93k and its Fab fragment confirmed that the 93k epitope was exposed in a prefusion conformation of glycoprotein B (gB), indicating that mAb 93k could be used to identify residues involved in fusion initiation
To define the molecular interactions formed between native gB and mAb 93k, a 2.8-Å structure of the gB-93k Fab complex was generated by using single particle cryo-EM, coupled with stringent particle selection and validation of local resolution (ResMap34), and feature resolvability through Q-score assignment (MapQ35) to amino acid side chains (Fig. 2a–d; Supplementary Figs. 1–3; Supplementary Tables 1–4; Supplementary Movie 1 and 2)
Summary
Members of the Herpesviridae, including the medically important alphaherpesvirus varicellazoster virus (VZV), induce fusion of the virion envelope with cell membranes during entry, and between cells to form polykaryocytes in infected tissues. We report here a 2.8 Å cryogenic-electron microscopy structure of native gB recovered from VZV-infected cells, in complex with a human monoclonal antibody, 93k. This high-resolution structure guided targeted mutagenesis at the gB-93k interface, providing compelling evidence that a domain spatially distant from the gB fusion loops is critical for herpesvirus fusion, revealing a potential new target for antiviral therapies. Only lowresolution structures (>24 Å) of herpesvirus gB in a putative prefusion form have been identified on exosomes derived from HSV-1 gB transfected cells and on HCMV particles using cryogenic electron tomography (cryo-ET)[10,13]. Adverse health effects are directly linked to the capability of VZV to overcome the usual constraint against fusion between differentiated host cells, causing fusion of ganglion neurons and satellite cells associated with postherpetic neuralgia (PHN), and fusion of vascular endothelial cells (giant cell arteritis) linked to strokes[27,28,29]
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