Structural study identifies target for broad-spectrum antivirals against herpesviruses

Human herpesviruses comprise the alpha, beta, and gamma subfamilies and are a widely prevalent group of DNA-enveloped viruses, capable of establishing lifelong latent infections in humans and causing various diseases. Among them, herpes simplex virus (HSV) belongs to the alpha herpesvirus group and infects a wide population, causing symptoms like oral or genital herpes. As an enveloped virus, HSV possesses a series of glycoproteins involved in virus recognition, adhesion, and infection processes. Among these, gB serves as the viral fusion protein, mediating the fusion between the virus and host cell membranes, and it is highly conserved across the entire herpesvirus family. Therefore, gB represents an ideal antiviral drug or antibody target. However, the lack of structural information on neutralizing epitopes for HSV has hindered the design of antibody drugs and vaccine targets.

The research team successfully purified the HSV-1 gB/D48 Fab complex using the 293F expression system. They validated through in vitro binding and neutralization assays that the D48 antibody efficiently neutralized HSV-1 virus infection by binding to gB. Subsequently, they resolved the structure of HSV-1 gB bound to D48 at a resolution of 3.04 Å using cryo-electron microscopy. The structure revealed that HSV-1 gB consists of five distinct domains, with D48 Fab primarily binding to the DII structural domain. Specifically, residues R418, D422, N430, H433, and Q438 from the LCDR1, LCDR3, and FR2 of the D48 light chain were found to interact polarly with DII, and alanine mutations at these key residues significantly reduced the interaction between HSV-1 gB and D48.

Upon obtaining high-resolution complex structures of neutralizing antibodies bound to HSV-1 gB, the research team performed a parallel comparison of the neutralizing epitopes of HCMV and EBV gB. They found that the neutralizing antibodies SM5-1 for HCMV and 3A3 for EBV also bind to the DII structural domain of gB. Further, they discovered the cross-herpesvirus conserved nature of these domains. The footprints of the antibodies' binding were not found to overlap with conserved residues, suggesting the likely existence of antibodies with broad-spectrum neutralizing activity against herpesviruses (Fig. 1J). Additionally, the team compared the structures of the DII domains of HSV, HCMV, and EBV gBs in complex with antibodies to their corresponding pre-fusion conformations. This comparison yielded recombinant structures showing that the DII domain in the pre-fusion conformation retains the ability to bind neutralizing antibodies, indicating a conservative antigenic epitope presentation in both pre-fusion and post-fusion states.

In conclusion, this study innovatively proposes that the gB DII domain within the herpesvirus family constitutes a broadly conserved neutralizing epitope structural domain. It highlights the exposure of antigenic epitopes in both pre-fusion and post-fusion conformations, providing crucial insights for the development of broad-spectrum drugs and vaccines against herpesviruses.