Spatial Configuration of Hepatitis E Virus Antigenic Domain

Abstract

Hepatitis E virus (HEV) is a human pathogen that causes acute hepatitis. When an HEV capsid protein containing a 52-amino-acid deletion at the C terminus and a 111-amino-acid deletion at the N terminus is expressed in insect cells, the recombinant HEV capsid protein can self-assemble into a T‫1؍‬ virus-like particle (VLP) that retains the antigenicity of the native HEV virion. In this study, we used cryoelectron microscopy and image reconstruction to show that anti-HEV monoclonal antibodies bind to the protruding domain of the capsid protein at the lateral side of the spikes. Molecular docking of the HEV VLP crystal structure revealed that Fab224 covered three surface loops of the recombinant truncated second open reading frame (ORF2) protein (PORF2) at the top part of the spike. We also determined the structure of a chimeric HEV VLP and located the inserted B-cell tag, an epitope of 11 amino acids coupled to the C-terminal end of the recombinant ORF2 protein. The binding site of Fab224 appeared to be distinct from the location of the inserted B-cell tag, suggesting that the chimeric VLP could elicit immunity against both HEV and an inserted foreign epitope. Therefore, the T‫1؍‬ HEV VLP is a novel delivery system for displaying foreign epitopes at the VLP surface in order to induce antibodies against both HEV and the inserted epitope.Hepatitis E virus (HEV) is a causative agent of acute hepatitis in humans and is primarily transmitted via the fecal-oral route. HEV is thus resistant to the low pH and digestive enzymes associated with the stomach and gastrointestinal tract. HEV regularly causes epidemics in many tropical and subtropical countries. In India, 101 outbreaks were confirmed by serological analysis in the state of Maharashtra in the last 5 years (6), and the lifetime risk of HEV infection exceeds 60% (28). Sporadic cases have also been reported in regions where HEV is endemic, as well as in areas where it is not endemic. Although some of these cases were associated with travel, many cases involved patients without a history of travel to regions where HEV is endemic. Accumulating evidence suggests that sporadic infection occurs through a zoonotic route and is not limited to developing countries. Seroprevalence suggests hepatitis E infection may also be prevalent in high-income countries (21), such as the United States (17), the United Kingdom (3), and Japan (18). The overall mortality rate of HEV infection during an outbreak generally ranges from 1 to 15%, and the highest mortality occurs in pregnant women, with fatality rates of up to 30% (19).The HEV virion is composed of a 7.2-kb single-stranded RNA molecule and a 32-to 34-nm icosahedral capsid. The HEV genome contains three open reading frames (ORFs).The capsid protein, encoded by the second open reading frame (ORF2), located at the 3Ј terminus of the genome, comprises 660 amino acids and is responsible for most capsid-related functions, such as assembly, host interaction, and immunogenicity. Recombinant ORF2 proteins can induce antibodies that block...

Structural basis for the neutralization of hepatitis E virus by a cross-genotype antibody

“…Meanwhile, this residue was also reported to be one of the several essential residues for host cell interaction [9]. To have a better spatial view of all the key epitope sites, i.e., the potential receptor binding sites, we mapped all the residues that have been shown to be involved in binding to the host cell ( Figure 7, Table 2 and Supplementary information, Figure S11) on the surface of T = 3 virion-sized particle [31] ( Figure 7A) and T = 1 HEV VLP [9,10,32] (Figure 7B). Interestingly all of these residues within E2 domain are located either in the dimerization region or in the groove region.…”

The Hepatitis E Virus Capsid C-Terminal Region Is Essential for the Viral Life Cycle: Implication for Viral Genome Encapsidation and Particle Stabilization

“…Genetic deletions or cellular processing resulting in the loss of the N-terminal 111 or 13 amino acids (aa) or of the C-terminal 52 aa (C52aa) yielded capsid protein capable of directing the formation of the HEV small (S) or large (L) VLPs (3)(4)(5). Particle formation was required for C52aa abbreviation, limiting the structural analysis of the resulting particles (3,4,(6)(7)(8)(9)(10). However, the contribution of the C52aa-encoding sequence was confirmed by both in vivo (attenuated infectivity of the point mutant virus in nonhuman primates) and in vitro (reduced RNA synthesis by RNA-dependent RNA polymerase [RdRp]) assays (11)(12)(13)(14).…”

Development of Enzyme-Linked Immunosorbent Assays Using 2 Truncated ORF2 Proteins for Detection of IgG Antibodies Against Hepatitis E Virus

“…The infection is lifethreatening during pregnancy, causing fatal and fulminant hepatitis with a high rate of miscarriage and premature birth [7]. Epidemiological studies have reported a mortality rate of up to 30% in pregnant women [7].…”

“…According to the phylogenetic analysis, HEV has 5 genotypes with different geographical distributions and hosts [7]. Humans may cause serious consequences in pregnant women and patients with chronic liver disease [2,7]. The infection is lifethreatening during pregnancy, causing fatal and fulminant hepatitis with a high rate of miscarriage and premature birth [7].…”

“…Its genome consists of a positive single-stranded RNA containing 3 overlapping open reading frames (ORFs), ORF1, ORF2, and ORF3 [5,6]. According to the phylogenetic analysis, HEV has 5 genotypes with different geographical distributions and hosts [7]. Humans may cause serious consequences in pregnant women and patients with chronic liver disease [2,7].…”