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Journal of Virology, June 2005, p. 7629-7640, Vol. 79, No. 12
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.12.7629-7640.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Murine Coronavirus Evolution In Vivo: Functional Compensation of a Detrimental Amino Acid Substitution in the Receptor Binding Domain of the Spike Glycoprotein
Sonia Navas-Martin,*
Susan T. Hingley,
and
Susan R. Weiss
Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
Received 29 November 2004/
Accepted 7 February 2005
Murine coronavirus A59 strain causes mild to moderate hepatitis in mice. We have previously shown that mutants of A59, unable to induce hepatitis, may be selected by persistent infection of primary glial cells in vitro. These in vitro isolated mutants encoded two amino acids substitutions in the spike (S) gene: Q159L lies in the putative receptor binding domain of S, and H716D, within the cleavage signal of S. Here, we show that hepatotropic revertant variants may be selected from these in vitro isolated mutants (Q159L-H716D) by multiple passages in the mouse liver. One of these mutants, hr2, was chosen for more in-depth study based on a more hepatovirulent phenotype. The S gene of hr2 (Q159L-R654H-H716D-E1035D) differed from the in vitro isolates (Q159L-H716D) in only 2 amino acids (R654H and E1035D). Using targeted RNA recombination, we have constructed isogenic recombinant MHV-A59 viruses differing only in these specific amino acids in S (Q159L-R654H-H716D-E1035D). We demonstrate that specific amino acid substitutions within the spike gene of the hr2 isolate determine the ability of the virus to cause lethal hepatitis and replicate to significantly higher titers in the liver compared to wild-type A59. Our results provide compelling evidence of the ability of coronaviruses to rapidly evolve in vivo to highly virulent phenotypes by functional compensation of a detrimental amino acid substitution in the receptor binding domain of the spike glycoprotein.
* Corresponding author. Mailing address: Department of Microbiology, University of Pennsylvania, School of Medicine, 36th Street and Hamilton Walk, Philadelphia, PA 19104-6076. Phone: 215-898-4672. Fax: 215-573-4858 E-mail: snavas{at}mail.med.upenn.edu.
Present address: Department of Pathology, Microbiology and Immunology, Philadelphia College of Osteopathic Medicine, Philadelphia, Pa.
Journal of Virology, June 2005, p. 7629-7640, Vol. 79, No. 12
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.12.7629-7640.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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Copyright © 2005 by the American Society for Microbiology. All rights reserved.