Structures of Hepatitis B Virus Core- and e-Antigen Immune Complexes Suggest Multi-point Inhibition

Abstract

Hepatitis B virus (HBV) is the leading cause of liver disease worldwide. While an adequate vaccine is available, current treatment options are limited, not highly effective, and associated with adverse effects, encouraging the development of alternative therapeutics. The HBV core gene encodes two different proteins: core, which forms the viral nucleocapsid, and pre-core, which serves as an immune modulator with multiple points of action. The two proteins mostly have the same sequence, although they differ at their N and C termini and in their dimeric arrangements. Previously, we engineered two human-framework antibody fragments (Fab/scFv) with nano- to picomolar affinities for both proteins. Here, by means of X-ray crystallography, analytical ultracentrifugation, and electron microscopy, we demonstrate that the antibodies have non-overlapping epitopes and effectively block biologically important assemblies of both proteins. These properties, together with the anticipated high tolerability and long half-lives of the antibodies, make them promising therapeutics.

Capsids of hepatitis B virus e antigen with authentic C termini are stabilized by electrostatic interactions

“…While this is plausible for most of the mutations, the peripheral location of E113 in the e antigen dimer suggests that there may be a different mechanism for this residue. The e antigen dimer can convert to a core antigen dimer‐like conformation and assemble into core‐like capsids . It may be that the E113Q mutation interferes with the assembly process by reducing the electrostatic interaction with the C termini of the adjacent subunit, much as described here.…”

“…). The in vitro transitions to capsid assembly‐competent conformations are mediated by reduction . The addition of the basic C‐terminal residues in the Cp(‐10)151 and Cp(‐10)154 constructs enhances the extent of this transition, as judged by formation for both constructs of ~ 85% capsids (Fig.…”

“…The authors suggest this is due to drug‐induced aggregation of HBeAg capsids formed from nonsecreted protein. We have shown that antibodies which target HBcAg assembly also block HBeAg capsid assembly . Targeting HBeAg with drugs or antibodies, which may reduce its levels in patients with chronic hepatitis, may be of therapeutic value.…”

Virus Assembly Antagonists from Redesigned Antibodies

“…In HBeAg, the dimer interface is antiparallel, held in place by a disulfide from helix 3 to the propeptide (DiMattia et al, 2013). The HBeAg structure from Eren et al (2018) has a monomer-monomer angle that is substantially different from the angle in the previously determined HBeAg structure (DiMattia et al, 2013) ( Figure 1B). Given the structural changes observed in HBeAg and HBcAg structures and in molecular dynamics simulations Zlotnick, 2016, Hadden et al, 2018), both are flexible proteins and binding to antibodies can alter their conformations and activities.…”

“…In this issue of Structure, Wingfield and colleagues (Eren et al, 2018) present a new approach to fight CHB: targeting HBeAg and dimeric HBcAg. They present three crystal structures of HBeAg and HBcAg dimers in complex with a Fab fragment or an scFV that binds with sub-nanomolar affinity (Zhuang et al, 2017).…”