The Capsid (ORF2) Protein of Hepatitis E Virus in Feces Is C-Terminally Truncated

The hepatitis E virus (HEV) is a causative agent of hepatitis E. HEV virions in circulating blood and culture media are quasi-enveloped, while those in feces are nonenveloped. The capsid (ORF2) protein associated with an enveloped HEV virion is reported to comprise the translation product of leucine 14/methionine 16 to 660 (C-terminal end). However, the nature of the ORF2 protein associated with fecal HEV remains unclear. In the present study, we compared the molecular size of the ORF2 protein among fecal HEV, cell-culture-generated HEV (HEVcc), and detergent-treated protease-digested HEVcc. The ORF2 proteins associated with fecal HEV were C-terminally truncated and showed the same size as those of the detergent-treated protease-digested HEVcc virions (60 kDa), in contrast to those of the HEVcc (68 kDa). The structure prediction of the ORF2 protein (in line with previous studies) demonstrated that the C-terminal region (54 amino acids) of an ORF2 protein is in flux, suggesting that proteases target this region. The nonenveloped nondigested HEV structure prediction indicates that the C-terminal region of the ORF2 protein moves to the surface of the virion and is unnecessary for HEV infection. Our findings clarify the maturation of nonenveloped HEV and will be useful for studies on the HEV lifecycle.

The Hepatitis E Virus Open Reading Frame 2 Protein: Beyond Viral Capsid

Hepatitis E virus (HEV) is a zoonotic pathogen causing hepatitis in both human and animal hosts, which is responsible for acute hepatitis E outbreaks worldwide. The 7.2 kb genome of the HEV encodes three well-defined open reading frames (ORFs), where the ORF2 translation product acts as the major virion component to form the viral capsid. In recent years, besides forming the capsid, more functions have been revealed for the HEV-ORF2 protein, and it appears that HEV-ORF2 plays multiple functions in both viral replication and pathogenesis. In this review, we systematically summarize the recent research advances regarding the function of the HEV-ORF2 protein such as application in the development of a vaccine, regulation of the innate immune response and cellular signaling, involvement in host tropism and participation in HEV pathogenesis as a novel secretory factor. Progress in understanding more of the function of HEV-ORF2 protein beyond the capsid protein would contribute to improved control and treatment of HEV infection.

The fate of Hepatitis E virus capsid protein is regulated by an Arginine-Rich Motif

Producing multifunctional proteins is one of the major strategies developed by viruses to condense their genetic information. Here, we investigated the molecular determinants of the multifunctionality of hepatitis E virus (HEV) ORF2 capsid protein. We previously identified 3 isoforms of ORF2 which are partitioned in different subcellular compartments to perform distinct functions. Notably, the infectious ORF2 (ORF2i) protein is the structural component of the virion, whereas the genome-free secreted and glycosylated ORF2 proteins likely act as a humoral immune decoy. We identified a 5 amino acid Arginine-Rich Motif (ARM) located in the ORF2 N-terminal region as a central regulator of the subcellular localizations and functions of ORF2 isoforms. We showed that the ARM controls ORF2 nuclear translocation, promoting regulation of host antiviral responses. This motif also regulates the dual topology and functionality of ORF2 signal peptide, leading to the production of either cytosolic infectious ORF2i or reticular non-infectious glycosylated ORF2 forms. Furthermore, the ARM likely serves as a cleavage site of the glycosylated ORF2 protein. Finally, it promotes ORF2 membrane association that is likely essential for particle assembly. In conclusion, our observations highlight ORF2 ARM as a unique central regulator of ORF2 addressing that finely controls the HEV lifecycle.

OASL Triggered by Novel Goose Astrovirus via ORF2 Restricts Its Replication

ABSTRACT Although astroviruses causes enteric diseases and encephalitis in humans and nephritis and hepatitis in poultry, astrovirus infection is thought to be self-limiting. However, little is known about its molecular mechanism. In this study, we found that a novel goose astrovirus (GAstV), GAstV-GD, and its open reading frame 2 (ORF2) could efficiently activate the innate immune response and induce a high level of OASL in vitro and in vivo. The truncation assay for ORF2 further revealed that the P2 domain of ORF2 contributed to stimulating OASL, whereas the acidic C terminus of ORF2 attenuated such activation. Moreover, the overexpression and knockdown of OASL could efficiently restrict and promote the viral replication of GAstV-GD, respectively. Our data not only give novel insights for elucidating self-limiting infection by astrovirus but also provide virus and host targets for fighting against astroviruses. IMPORTANCE Astroviruses cause gastroenteritis and encephalitis in human, and nephritis, hepatitis, and gout disease in poultry. However, the host immune response activated by astrovirus is mostly unknown. Here, we found that a novel goose astrovirus, GAstV-GD, and its ORF2 protein could efficiently induce a high level of OASL in vitro and in vivo, which could feed back to restrict the replication of GAstV-GD, revealing novel innate molecules triggered by astroviruses and highlighting that the ORF2 of GAstV-GD and OASL can be potential antiviral targets for astroviruses.

Synthetic Peptides Containing Three Neutralizing Epitopes of Genotype 4 Swine Hepatitis E Virus ORF2 induced Protection against Swine HEV Infection in Rabbit

Genotype 4 hepatitis E virus (HEV) is a zoonotic pathogen transmitted to humans through food and water. Previously, three genotype 4 swine HEV ORF2 peptides (407EPTV410, 410VKLYTS415, and 458PSRPF462) were identified as epitopes of virus-neutralizing monoclonal antibodies that partially blocked rabbit infection with swine HEV. Here, individual and tandem fused peptides were synthesized, conjugated to keyhole limpet hemocyanin (KLH), then evaluated for immunoprotection of rabbits against swine HEV infection. Forty New Zealand White rabbits were randomly assigned to eight groups; groups 1 thru 5 received three immunizations with EPTV-KLH, VKLYTS-KLH, PSRPF-KLH, EPTVKLYTS-KLH, or EPTVKLYTSPSRPF-KLH, respectively; group 6 received truncated swine HEV ORF2 protein (sp239), and group 7 received phosphate-buffered saline. After an intravenous swine HEV challenge, all group 7 rabbits exhibited viremia and fecal virus shedding by 2–4 weeks post challenge (wpc), seroconversion by 4–9 wpc, elevated alanine aminotransferase (ALT) at 2 wpc, and severe liver lymphocytic venous periphlebitis. Only 1–2 rabbits/group in groups 1–4 exhibited delayed viremia, fecal shedding, seroconversion, increased ALT levels, and slight liver lymphocytic venous periphlebitis; groups 5–6 showed no pathogenic effects. Collectively, these results demonstrate that immunization with a polypeptide containing three genotype 4 HEV ORF2 neutralizing epitopes completely protected rabbits against swine HEV infection.

Hepatitis E virus truncated capsid protein as a potential carrier of exogenous antigens for the development of chimeric virus-like particle vaccines

Background: Virus like particle (VLP), a multiprotein structure which is assembled automatically, can stimulate robust immune responses due to an appropriate size, repetitive epitopes, and a structure similar to native virions. Utilizing VLPs as vaccine carriers to present exogenous antigens is a promising and challenging field in vaccine design. Hence, this study aims to investigate the potential of Hepatitis E virus (HEV) truncated capsid protein as a VLP carrier presenting foreign antigens in vaccine design.Results: S and M domains of HEV ORF2 protein (aa112-455) were selected as an optimal carrier (CaSM). The exogenous antigen Seq8 containing three immunogenic domains from three different foot-and-mouth disease virus (FMDV) strains was linked to the C-terminal of CaSM to construct a chimeric VLP vaccine candidate (CaSM-Seq8). Morphological analysis showed that CaSM-Seq8 self-assembled into VLPs with a diameter of approximately 26 nm, similar to the VLPs of CaSM alone but smaller than native HEV virions. Further, the thermal stability and the proteolysis resistance of Seq8 were enhanced when carried by CaSM. The antigenicity analysis revealed a more robust reactivity against anti-FMDV specific antibodies when Seq8 was presented on the CaSM particles. Upon injection into mice, anti-FMDV IgGs induced by CaSM-Seq8 appeared earlier, increased faster, and maintained higher levels for a longer time than those induced by Seq8 antigen alone or a commercial inactivated FMDV vaccine.Conclusions: This study demonstrates the potential of the HEV truncated capsid protein VLPs as a presenting-platform of exogenous antigens in vaccine design and promising preliminary results on chimeric VLP vaccine against foot-and-mouth disease.