Heat shock protein 70 in lung and kidney of specific-pathogen-free chickens is a receptor-associated protein that interacts with the binding domain of the spike protein of infectious bronchitis virus.

Avian infectious bronchitis virus (IBV) is a member of the family Coronaviridae. A binding domain that mediates the attachment of the virus to its receptor has been identified in the S1 protein of prototype IBV strain M41. In this study, we identified this binding domain in a different strain, as well as the cellular proteins that interact with it. First, we expressed the S1 proteins (residues 19-270) of M41 and another isolate, SCZJ3, and compared the binding capacities of recombinant S1-M41 and S1-SCZJ3 to host tissues. Protein histochemistry showed that both S1-M41 and S1-SCZJ3 could bind to lung and kidney, and that recombinant S1-SCZJ3 displayed a distinctive staining pattern in the proventriculus. Recombinant S1-SCZJ3 was then employed to purify binding-associated proteins in lung, kidney, and proventriculus. Using an affinity chromatography assay, two common bands of about 60 kDa and 70 kDa were obtained from the total tissue proteins. These protein bands were identified by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) as protein disulfide isomerase (PDI) and heat shock protein 70 (HSP70). Finally, infection of chicken embryo kidney (CEK) cells by SCZJ3 was found to be inhibited by anti-HSP70 but not anti-PDI polyclonal antibody. These data indicate that HSP70 is part of the receptor complex of IBV and might help to understand the mechanism of S-mediated cell entry of IBV.