Amino-terminal epitopes are exposed when full-length open reading frame 2 of hepatitis E virus is expressed in Escherichia coli, but carboxy-terminal epitopes are masked.

Abstract

We constructed a panel of overlapping and non-overlapping fragments of cDNA derived from open reading frame 2 (ORF2) of hepatitis E virus (HEV) and fused to the gene encoding glutathione S-transferase (GST), from which proteins were expressed in Escherichia coli. IgG-specific immunoreactivity against each protein was measured by Western immunoblotting using sera from experimentally infected Rhesus macaques (Macaca mulatta) or from HEV-infected patients. Under these conditions, full-length ORF2 protein (GST-ORF2) was strongly reactive with acute-phase sera from either macaques or patients, but was poorly reactive with convalescent sera. Recombinant protein GST-ORF2.3, representing amino acids 1-110 of the 660 encoded by ORF2, demonstrated a pattern of reactivity largely indistinguishable from the full-length protein. Conversely, GST-ORF2.1, representing amino acids 394-660 of the ORF2 protein was strongly reactive with both acute- and convalescent-phase sera. Extension of GST-ORF2.1 towards the N-terminus led to a progressive loss of convalescent-phase reactivity, apparent with as few as 20 additional HEV-specific amino acids. Deletion of 40 or more amino acids from the N-terminus of ORF2.1 also led to reduced convalescent-phase reactivity, however a protein representing this "reactive" region, containing amino acids 394-473, was poorly reactive, suggesting that the convalescent-reactive epitopes are conformational. Expression of full-length ORF2 protein in E. coli therefore masks the convalescent-reactive epitopes within the C-terminal part of the protein, without affecting N-terminal, acute-reactive epitopes.