PURIFIED, SOLUBLE RECOMBINANT MOUSE HEPATITIS-VIRUS RECEPTOR, BGP1(B), AND BGP2 MURINE CORONAVIRUS RECEPTORS DIFFER IN MOUSE HEPATITIS-VIRUS BINDING AND NEUTRALIZING ACTIVITIES

Mouse hepatitis virus receptor (MHVR) is a murine biliary glycoprotein (Bgp1(a)). Purified, soluble MHVR expressed from a recombinant vaccin ia virus neutralized the infectivity of the A59 strain of mouse hepati tis virus (MHV A59) in a concentration dependent manner. Several ancho red murine Bgps in addition to MHVR can also function as MHV-A59 recep tors when expressed at high levels in nonmurine cells. To investigate the interactions of these alternative MHVR glycoproteins with MHV, we expressed and purified to apparent homogeneity the extracellular domai ns of several murine Bgps as soluble, six-histidine-tagged glycoprotei ns, using a baculovirus expression system. These include MHVR isoforms containing four or two extracellular domains and the corresponding Bg p1(b) glycoproteins from MHV-resistant SJL/J mice, as well as Bgp2 and truncation mutants of MHVR and Bgp1(b) comprised of the first two imm unoglobulin-like domains. The soluble four-domain MHVR glycoprotein (s MHVR[1-4]) had fourfold more MHV-A59 neutralizing activity than the co rresponding soluble Bgp1(b) (sBgp1(b)) glycoprotein and at least 1,000 -fold more neutralizing activity than sBgp2. Although virus binds to t he N-terminal domain (domain 1), soluble truncation mutants of MHVR an d Bgp1(b) containing only domains 1 and 2 bound virus poorly and had 1 0- and 300-fold less MHV-A59 neutralizing activity than the correspond ing four-domain glycoproteins. In contrast, the soluble MHVR glycoprot ein containing domains 1 and 4 (sMHVR[1,4]) had as much neutralizing a ctivity as the four-domain glycoprotein, sMHVR[1-4]. Thus, the virus n eutralizing activity of MHVR domain 1 appears to be enhanced by domain 4. The sBgp1(b)[1-4] glycoprotein had 500-fold less neutralizing acti vity for MHV-JHM than for MHV-A59. Thus, MHV strains with differences in S-glycoprotein sequence, tissue tropism, and virulence can differ i n the ability to utilize the various murine Bgps as receptors.