MUTATIONAL ANALYSIS OF THE VIRUS AND MONOCLONAL-ANTIBODY BINDING-SITES IN MHVR, THE CELLULAR RECEPTOR OF THE MURINE CORONAVIRUS MOUSE HEPATITIS-VIRUS STRAIN A59

The primary cellular receptor for mouse hepatitis virus (MHV), a murin e coronavirus, is MHVR (also referred to as Bgp1(a) or C-CAM), a trans membrane glycoprotein with four immunoglobulin-like domains in the mur ine biliary glycoprotein (Bgp) subfamily of the carcinoembryonic antig en (CEA) family. Other murine glycoproteins in the Bgp subfamily, incl uding Bgp1(b) and Bgp2, also can serve as MHV receptors when transfect ed into MHV-resistant cells. Previous studies have shown that the 108- amino-acid N-terminal domain of MHVR is essential for virus receptor a ctivity and is the binding site for monoclonal antibody (MAb) CCl, an antireceptor MAb that blocks MHV infection in vivo and in vitro. To fu rther elucidate the regions of MHVR required for virus receptor activi ty and MAb CCl binding, we constructed chimeras between MHVR and other members of the CEA family and tested them for MHV strain A59 (MHV-A59 ) receptor activity and MAb CCl binding activity. In addition, we used site-directed mutagenesis to introduce selected amino acid changes in to the N-terminal domains of MHV and these chimeras and tested the abi lities of these mutant glycoproteins to bind MAb CCl and to function a s MHV receptors. Several recombinant glycoproteins exhibited virus rec eptor activity but did not bind MAb CCl, indicating that the virus and MAb binding sites on the N-terminal domain of MHVR are not identical. Analysis of the recombinant glycoproteins showed that a short region of MHVR, between amino acids 34 and 52, is critical for MHV-A59 recept or activity. Additional regions of the N-terminal variable domain and the constant domains, however, greatly affected receptor activity. Thu s, the molecular contest in which the amino acids critical for MHV-A59 receptor activity are found profoundly influeuces the virus receptor activity of the glycoprotein.