Hepatitis E Virus (HEV) is one of the leading causes of acute viral hepatitis, with ~20 million HEV infections worldwide per annum, and mortality rates up to 25% in pregnant women. However, many aspects of the biology of the virus are poorly understood. HEV has a positive-sense single-stranded RNA genome. ORF1 encodes the non-structural polyprotein required for viral RNA replication. This polyprotein (sometimes termed pORF1) is predicted to contain seven domains based on sequence homology to related viruses and it is hypothesised that this polyprotein must undergo proteolysis to generate functional protein units. However, it is unknown if the pORF1 polyprotein undergoes full proteolysis, the potential locations of any cleavage boundaries and whether a viral or host cell protease is responsible.

We have adapted our in vitro-based proteolysis assays to investigate cleavage of HEV pORF1. In comparison to related RNA viruses, our data suggest that pORF1 has no auto-catalytic activity. Previous studies have shown that the liver-produced protease, thrombin, is essential for replication. In the presence of thrombin, we have shown that the ORF1 polyprotein undergoes specific proteolysis to produce eight distinct protein products. Combining bioinformatics with pORF1 truncations/mutagenesis, we have located the position of the pORF1 thrombin cleavage sites. Interestingly, these cleavage sites correspond to the junctions between the predicted pORF1 protein domains. Our data suggests that thrombin is an important cellular protease for controlling pORF1 proteolysis. Work is ongoing to understand the importance of each thrombin cleavage site in viral replication.

  • This is an open-access article distributed under the terms of the Creative Commons Attribution License.

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