Homology model and potential virus-capsid binding site of a putative HEV receptor Grp78

P239, a truncated construct of the hepatitis E virus (HEV) ORF2 protein, has been proven able to bind with a chaperone, Grp78, in both an in vitro co-immune precipitation test and an in vivo cell model. We previously solved the crystal structure of E2s--the C-terminal domain of p239 involved in host interactions. In the present study, we built a 3D structure of Grp78 using homology modeling methods, and docked this molecule with E2s using the Zdockpro module of the InsightII software package. The modeled Grp78 structure was deemed feasible by profile 3D evaluation and molecular dynamic simulations. The docking result consists of six clusters of distinct complexes and C035 was selected as the most reasonable. The interacting interface of the predicted complex is comprised of the Grp78 linker region and nucleotide binding domain along with the E2s groove region and surrounding loops. Using energy, hydrogen bond and solvent accessible surface analyses, we identified a series of key residues that may be involved in the Grp78:E2s interaction. By comparing with the known structure of the Hsp70:J complex, we further concluded that the interaction of Grp78 and E2s could interrupt binding of Grp78 with the J domain, and in turn diminish or even eliminate the binding ability of the Grp78 substrate binding domain. The predicted series of key residues also provides clues for further research that should improve our understanding of the fundamental molecular mechanisms of HEV infection.