Structure and Genome of Hepatitis E Virus

Structure and Genome of Hepatitis E Virus

Hepatitis E virus, discovered in 1983 by immune electron microscopy and first cloned in 1990.

Structure of Hepatitis E Virus

  • HEV is classified in the Calciviridae family because of its structural similarity to other calciviruses; however, it is now the sole member of the Hepeviridae family.
  • The virus is non enveloped (naked) with icosahedral symmetry measuring 27-30 nm diameter.
  • The genome is single stranded RNA genome with positive polarity and measure about 7.2 kb in length.

Structure of Hepatitis E Virus

  • Both immune and negative stain electron microscopy of human stool specimens have showed that the diameter of HEV is about 32 nm.
  • The surface of the virion has obvious spikes that are slightly less pronounced than those of Norovirus, but is clearly distinct from the smooth, featureless surface of the hepatitis A virus.
  • Based on genome sequences, five major genotypes have been identified.
  • The circulation of genotypes 1 and 2 viruses is maintained among only humans, while those of genotypes 3 and 4 are found in human as well as animals.
  • The viruses of genotype 5 are of avian origin, thought to be noninfectious to humans.
  • Although four of the five genotypes infect human ,only one HEV serotype has been found in human.

Genome of Hepatitis E Virus

  • The HEV genome is a single-stranded, positive-sense RNA molecule and 7.2 kb in size.
Genome of Hepatitis E Virus
Source: Vijay Kumar, Virology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
  • Genomic RNA is polyadenylated and contains 3 ORFs.
  • ORF1 encodes the nonstructural proteins, ORF2 encodes the capsid protein, and ORF3 encodes a small multifunctional protein.
  • The ORF2 and ORF3 proteins are translated from a single, bicistronic mRNA.
  • Located near the 5′-end, ORF1 encodes a non-structural polyprotein with multiple functional domains, including those for methyltransferase, protease, helicase, and polymerase.
  • The viral capsid protein (CP) is encoded by ORF2 near the 3′-end.
  • ORF3, which partially overlaps with the other 2 ORFs, codes for an immunogenic protein of unknown function.
  • ORF3 encodes a 113 or 114 aa phosphoprotein, depending upon the genotype.
  • The ORF2 capsid protein, HEV-CP, contains a total of 660 amino acid residues.
  • At the HEV-CP N terminus is a signal peptide followed by an arginine-rich domain that potentially play a role in viral RNA encapsidation during assembly.
  • HEV-CP is a key antigen that stimulates the host immune response, and 6 antigenic domains have been identified.
  • One neutralization site has been mapped to the polypeptide region between amino acids 452 and 617.

Structure and Genome of Hepatitis E Virus

Structure and Genome of Hepatitis E Virus

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