title: A 12-amino acid stretch in the hypervariable region of the spike protein S1 subunit is critical for cell fusion activity of mouse hepatitis virus.
abstract: The spike (S) glycoprotein of mouse hepatitis virus (MHV) plays a major role in the viral pathogenesis. It is often processed into the N-terminal S1 and the C-terminal S2 subunits that were evidently important for binding to cell receptor and inducing cell-cell fusion, respectively. As a consequence of cell-cell fusion, most of the naturally occurring infections of MHV are associated with syncytia formation. So far, only MHV-2 was identified to be fusion-negative. In this study, the S gene of MHV-2 was molecularly cloned, and the nucleotide sequence was determined. The MHV-2 S protein lacks a 12-amino acid stretch in the S1 hypervariable region from amino acid residue 446 to 457 when compared with the fusion-positive strain MHV-JHM. In addition, there are three amino acid substitutions in the S2 subunit, Tyr-1144 to Asp, Glu-1165 to Asp, and Arg-1209 to Lys. The cloned MHV-2 S protein exhibited the fusion-negative property in DBT cells as the intrinsic viral protein. Furthermore, similar to the fusion-positive MHV-JHM strain, proteolytic cleavage activity was detected both in DBT cells infected with the fusion-negative MHV-2 and in the transfected cells that expressed the cloned MHV-2 S protein. Domain swapping experiments demonstrated that the 12-amino acid stretch missing in the MHV-2 S1 subunit, but not the proteolytic cleavage site, was critical for the cell-fusion activity of MHV.
authors.affiliation: Institute of Biochemistry, College of Medicine, National Taiwan University, Taipei 100, Taiwan.
authors.forename: C W
authors.initials: CW
authors.lastname: Tsai
authors.forename: S C
authors.initials: SC
authors.lastname: Chang
authors.forename: M F
authors.initials: MF
authors.lastname: Chang
mesh_terms: D000818:Animals; D001483:Base Sequence; D002459:Cell Fusion / Q000502:physiology*; D002460:Cell Line; D003001:Cloning, Molecular; D017931:DNA Primers; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D006517:Murine hepatitis virus / Q000235:genetics / Q000502:physiology*; D017384:Sequence Deletion; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: D017931:DNA Primers; D008562:Membrane Glycoproteins; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus