Characterization of a new gene that encodes a functional MHV receptor and progress in the identification of the virus-binding site(s)

Several splice variants of the murine biliary glycoprotein 1 (Bgp 1) gene in the carcinoembryonic antigen gene superfamily serve as cellular receptors for mouse hepatitis virus. RNAPCR and immunoblot analysis of the receptor in inbred mouse strains showed that the glycoproteins expressed in SJL/J mice are encoded by an allelic variant of the Bgp 1 gene, named Bgp 1(b). We recently cloned and characterized a second gene, Bgp 2, that encodes a functional MHV receptor glycoprotein which is not recognized by anti-M HVR MAb-CC1. A third gene related to Bgp 1 was cloned and expressed and shown to encode a soluble protein called Cea-10 that differs significantly in its N- terminal domain from Bgp 1 and Bgp 2. Chimeric proteins constructed between the different murine Bgps and point mutations in the prototype MHV receptor, Bgp 1(a) or MHVR, were analyzed to further characterize the MAb-CC1-binding and virus-binding domains within the N terminal domain of the receptor. Thus, the murine host for MHV expresses multiple splice variants of mRNAs encoded by several different Bgp-related genes which differ in their ability to serve as MHV receptors. The differential expression of these genes in different murine tissues may help to explain the tissue tropism of MHV strains.