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The N-Terminal Domain of the Murine Coronavirus Spike Glycoprotein Determines the CEACAM1 Receptor Specificity of the Virus Strain

Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104,¹ Department of Microbiology, University of Colorado Health Sciences Center, Denver, Colorado 80626²

Received 25 June 2002/ Accepted 15 October 2002

Using isogenic recombinant murine coronaviruses expressing wild-type murine hepatitis virus strain 4 (MHV-4) or MHV-A59 spike glycoproteins or chimeric MHV-4/MHV-A59 spike glycoproteins, we have demonstrated the biological functionality of the N-terminus of the spike, encompassing the receptor binding domain (RBD). We have used two assays, one an in vitro liposome binding assay and the other a tissue culture replication assay. The liposome binding assay shows that interaction of the receptor with spikes on virions at 37°C causes a conformational change that makes the virions hydrophobic so that they bind to liposomes (B. D. Zelus, J. H. Schickli, D. M. Blau, S. R. Weiss, and K. V. Holmes, J. Virol. 77: 830-840, 2003). Recombinant viruses with spikes containing the RBD of either MHV-A59 or MHV-4 readily associated with liposomes at 37°C in the presence of soluble mCEACAM1^a, except for S₄R, which expresses the entire wild-type MHV-4 spike and associated only inefficiently with liposomes following incubation with soluble mCEACAM1^a. In contrast, soluble mCEACAM1^b allowed viruses with the MHV-A59 RBD to associate with liposomes more efficiently than did viruses with the MHV-4 RBD. In the second assay, which requires virus entry and replication, all recombinant viruses replicated efficiently in BHK cells expressing mCEACAM1^a. In BHK cells expressing mCEACAM1^b, only viruses expressing chimeric spikes with the MHV-A59 RBD could replicate, while replication of viruses expressing chimeric spikes with the MHV-4 RBD was undetectable. Despite having the MHV-4 RBD, S₄R replicated in BHK cells expressing mCEACAM1^b; this is most probably due to spread via CEACAM1 receptor-independent cell-to-cell fusion, an activity displayed only by S₄R among the recombinant viruses studied here. These data suggest that the RBD domain and the rest of the spike must coevolve to optimize function in viral entry and spread.

This article has been cited by other articles:

• Zelus, B. D., Schickli, J. H., Blau, D. M., Weiss, S. R., Holmes, K. V. (2002). Conformational Changes in the Spike Glycoprotein of Murine Coronavirus Are Induced at 37{degrees}C either by Soluble Murine CEACAM1 Receptors or by pH 8. J. Virol. 77: 830-840 [Abstract] [Full Text]