Acquired fusion activity of a murine coronavirus MHV-2 variant with mutations in the proteolytic cleavage site and the signal sequence of the S protein.
The spike (S) protein of a nonfusogenic murine coronavirus, MHV-2, was compared to the S protein of a variant with fusion activity, MHV-2f. Two amino acids differed between the S proteins of these viruses; one was located in the signal sequence and the other was in the putative cleavage site. The amino acid at position 12 in the signal sequence was S in MHV-2 and C in MHV-2f. The amino acid sequence of the cleavage site of MHV-2 was HRARS, while that of MHV-2f was HRARR, showing one amino acid replacement at position 757. In DBT cells infected with MHV-2, the S protein was not cleaved, while the S protein of MHV-2f was cleaved. The S protein of MHV-2f expressed in a transient vaccinia virus expression system was cleaved and was fusogenic in contrast to the nonfusogenic activity of uncleaved MHV-2 S protein. Because the signal sequence is assumed to be removed from the mature S protein soon after synthesis, and because the S protein of MHV-2 was expressed on the cell surface in the same way as the S protein of MHV-2f, the difference in the signal sequence seemed to have had little effect on the transportation and the fusion activity of the S protein. These results showed that MHV-2 does not fuse cells due to the lack of cleavage of its S protein. This conclusion differs from studies on the activity of syncytium formation by the S proteins of fusogenic MHV-JHM and -A59 strains. Possible reasons for these differences in fusion activity are discussed.
Yamada
Y K
YK
Division of Experimental Animal Research, National Institute of Health, 4-7-1 Gakuen, Musashimurayama, Tokyo, Japan. ykyamada@nih.go.jp
Takimoto
K
K
Yabe
M
M
Taguchi
F
F
D001665:Binding Sites; D001692:Biological Transport; D002460:Cell Line; D003588:Cytopathogenic Effect, Viral; D015726:Giant Cells / Q000821:virology; D008561:Membrane Fusion; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008969:Molecular Sequence Data; D006517:Murine hepatitis virus / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D021382:Protein Sorting Signals / Q000235:genetics / Q000378:metabolism*; D064370:Spike Glycoprotein, Coronavirus; D014357:Trypsin / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
D008562:Membrane Glycoproteins; D021382:Protein Sorting Signals; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus; D014357:Trypsin