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.

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A C-terminal Hydrophobic Region is Required for Homo-Oligomerization of the Hepatitis E Virus Capsid (ORF2) Protein

Journal of Biomedicine and Biotechnology ◽

10.1155/s1110724301000262 ◽

2001 ◽

Vol 1 (3) ◽

pp. 122-128 ◽

Cited By ~ 11

Author(s):

Li Xiaofang ◽

Mohammad Zafrullah ◽

Faizan Ahmad ◽

Shahid Jameel

Keyword(s):

Amino Acids ◽

Hepatitis E Virus ◽

Hepatitis E ◽

Wild Type ◽

Hydrophobic Region ◽

Reading Frame ◽

Orf2 Protein ◽

Acute Form ◽

Open Reading Frame 2

Hepatitis E virus (HEV) is the causative agent of hepatitis E, an acute form of viral hepatitis. The open reading frame 2 (ORF2) of HEV encodes the viral capsid protein, which can self-oligomerize into virus-like particles. To understand the domains within this protein important for capsid biogenesis, we have carried out in vitro analyses of association and folding patterns of wild type and mutant ORF2 proteins. When expressedin vitroor in transfected cells, the ORF2 protein assembled as dimers, trimers and higher order forms. While N-terminal deletions upto 111 amino acids had no effect, the deletion of amino acids 585–610 led to reduced homo-oligomerization. This deletion also resulted in aberrant folding of the protein, as determined by its sensitivity to trypsin. This study suggests that a C-terminal hydrophobic region encompassing amino acids 585–610 of the ORF2 protein might be critical for capsid biogenesis.

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Antigenic Domains of the Open Reading Frame 2-Encoded Protein of Hepatitis E Virus

Journal of Clinical Microbiology ◽

10.1128/jcm.37.9.2863-2871.1999 ◽

1999 ◽

Vol 37 (9) ◽

pp. 2863-2871 ◽

Cited By ~ 38

Author(s):

Yury E. Khudyakov ◽

Elena N. Lopareva ◽

Danny L. Jue ◽

Tamara K. Crews ◽

S. P. Thyagarajan ◽

...

Keyword(s):

Synthetic Peptides ◽

Hepatitis E Virus ◽

Hepatitis E ◽

Open Reading Frame ◽

Reading Frame ◽

Orf2 Protein ◽

Positive Serum ◽

Antigenic Domains ◽

Open Reading Frame 2 ◽

Antigenic Epitopes

The antigenic composition of the hepatitis E virus (HEV) protein encoded by open reading frame 2 (ORF2) was determined by using synthetic peptides. Three sets of overlapping 18-, 25-, and 30-mer peptides, with each set spanning the entire ORF2 protein of the HEV Burma strain, were synthesized. All synthetic peptides were tested by enzyme immunoassay against a panel of 32 anti-HEV-positive serum specimens obtained from acutely HEV-infected persons. Six antigenic domains within the ORF2 protein were identified. Domains 1 and 6 located at the N and C termini of the ORF2 protein, respectively, contain strong immunoglobulin G (IgG) and IgM antigenic epitopes that can be efficiently modeled with peptides of different sizes. In contrast, antigenic epitopes identified within the two central domains (3 and 4) were modeled more efficiently with 30-mer peptides than with either 18- or 25-mers. Domain 2 located at amino acids (aa) 143 to 222 was modeled best with 25-mer peptides. A few 30-mer synthetic peptides derived from domain 5 identified at aa 490 to 579 demonstrated strong IgM antigenic reactivity. Several 30-mer synthetic peptides derived from domains 1, 4, and 6 immunoreacted with IgG or IgM with more than 70% of anti-HEV-positive serum specimens. Thus, the results of this study demonstrate the existence of six diagnostically relevant antigenic domains within the HEV ORF2 protein.

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Cellular Immune Responses in Acute Hepatitis E Virus Infection to The Viral Open Reading Frame 2 Protein

Viral Immunology ◽

10.1089/vim.2006.0053 ◽

2007 ◽

Vol 20 (1) ◽

pp. 56-65 ◽

Cited By ~ 57

Author(s):

Ruchi Srivastava ◽

Rakesh Aggarwal ◽

Shahid Jameel ◽

Pankaj Puri ◽

Vijay K. Gupta ◽

...

Keyword(s):

Virus Infection ◽

Immune Responses ◽

Hepatitis E Virus ◽

Hepatitis E ◽

Open Reading Frame ◽

Reading Frame ◽

Cellular Immune Responses ◽

Acute Hepatitis E ◽

Cellular Immune ◽

Open Reading Frame 2

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Antigenic Characterization of ORF2 and ORF3 Proteins of Hepatitis E Virus (HEV)

Viruses ◽

10.3390/v13071385 ◽

2021 ◽

Vol 13 (7) ◽

pp. 1385

Author(s):

Giulia Pezzoni ◽

Lidia Stercoli ◽

Eleonora Pegoiani ◽

Emiliana Brocchi

Keyword(s):

Hepatitis E Virus ◽

Hepatitis E ◽

Recombinant Antigen ◽

Open Reading Frame ◽

Reading Frame ◽

E Coli ◽

Antigenic Characterization ◽

Antigenic Properties ◽

Open Reading Frame 2

To evaluate the antigenic properties of Hepatitis E Virus (HEV) Open Reading Frame 2 and 3 (ORF2 and ORF3) codified proteins, we expressed different portions of ORF2 and the entire ORF3 in E. coli, a truncated ORF2, was also expressed in baculovirus. A panel of 37 monoclonal antibodies (MAbs) was raised against ORF2 (1–660 amino acids) and MAbs were mapped and characterized using the ORF2 expressed portions. Selected HEV positive and negative swine sera were used to evaluate ORF2 and ORF3 antigens’ immunogenicity. The MAbs were clustered in six groups identifying six antigenic regions along the ORF2. Only MAbs binding to the sixth ORF2 antigenic region (394–608 aa) were found to compete with HEV positive sera and efficiently catch the recombinant antigen expressed in baculovirus. The ORF2 portion from 394–608 aa demonstrated to include most immunogenic epitopes with 85% of HEV positive swine sera reacting against the region from 461–544 aa. Only 5% of the selected HEV sera reacted against the ORF3 antigen.

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Mapping of linear B cell epitopes on open reading frames 2- and 3-encoded proteins of hepatitis E virus using synthetic peptides

FEMS Microbiology Letters ◽

10.1111/j.1574-6968.1993.tb06176.x ◽

1993 ◽

Vol 109 (2-3) ◽

pp. 251-255 ◽

Cited By ~ 20

Author(s):

Pierre Coursaget ◽

Yves Buisson ◽

Nathalie Depril ◽

Pierre Cann ◽

Martine Chabaud ◽

...

Keyword(s):

B Cell ◽

Synthetic Peptides ◽

Hepatitis E Virus ◽

Hepatitis E ◽

Open Reading Frames ◽

B Cell Epitopes ◽

Encoded Proteins ◽

Reading Frames ◽

Linear B

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Hepatitis E Virus (HEV) Open Reading Frame 2 Antigen Kinetics in Human-Liver Chimeric Mice and Its Impact on HEV Diagnosis

The Journal of Infectious Diseases ◽

10.1093/infdis/jiz171 ◽

2019 ◽

Vol 220 (5) ◽

pp. 811-819 ◽

Cited By ~ 8

Author(s):

Ibrahim M Sayed ◽

Lieven Verhoye ◽

Claire Montpellier ◽

Florence Abravanel ◽

Jacques Izopet ◽

...

Keyword(s):

Density Gradient ◽

Hepatitis E Virus ◽

Gradient Analysis ◽

Hepatitis E ◽

Open Reading Frame ◽

Viral Rna ◽

Humanized Mice ◽

Molecular Diagnostic ◽

Reading Frame ◽

Open Reading Frame 2

Abstract Background Hepatitis E virus infection (HEV) is an emerging problem in developed countries. Diagnosis of HEV infection is based on the detection of HEV-specific antibodies, viral RNA, and/or antigen (Ag). Humanized mice were previously reported as a model for the study of HEV infection, but published data were focused on the quantification of viral RNA. However, the kinetics of HEV Ag expression during infection remains poorly understood. Methods Plasma specimens and suspensions of fecal specimens from HEV-infected and ribavirin-treated humanized mice were analyzed using HEV antigen–specific enzyme-linked immunosorbent assay, reverse transcription–quantitative polymerase chain reaction analysis, density gradient analysis, and Western blotting. Result Open reading frame 2 (ORF2) Ag was detected in both plasma and stool from HEV-infected mice, and levels increased over time. Contrary to HEV RNA, ORF2 Ag levels were higher in mouse plasma than in stool. Interestingly, ORF2 was detected in plasma from mice that tested negative for HEV RNA in plasma but positive for HEV RNA in stool and was detected after viral clearance in mice that were treated with ribavirin. Plasma density gradient analysis revealed the presence of the noninfectious glycosylated form of ORF2. Conclusion ORF2 Ag can be used as a marker of active HEV infection and for assessment of the effect of antiviral therapy, especially when fecal samples are not available or molecular diagnostic tests are not accessible.

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