Proteolytic cleavage of the murine coronavirus surface glycoprotein is not required for fusion activity.
A cDNA copy of the murine coronavirus [otherwise known as murine hepatitis virus (MHV)] surface (S) glycoprotein gene was isolated and expressed in DBT cells by using a recombinant vaccinia virus system. The expressed S protein induced extensive syncytium formation at neutral pH. Oligonucleotide mutagenesis was used to engineer an S protein gene in which codons for the proteolytic cleavage site, Arg-Arg-Ala-Arg-Arg, were replaced with an equal number of codons for amino acids with aliphatic or aliphatic hydroxyl side-chains. The mutated S protein was stably expressed in DBT cells and, in contrast to the wild-type protein, was not proteolytically cleaved. Nevertheless, the non-cleaved protein induced extensive syncytium formation. These results clearly indicate that the non-cleaved form of the MHV S protein is able to mediate cell membrane fusion. Thus proteolytic cleavage is not an absolute requirement for fusion activity.
Stauber
R
R
Institute of Virology, University of Würzburg, Germany.
Pfleiderera
M
M
Siddell
S
S
D000595:Amino Acid Sequence; D001483:Base Sequence; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008969:Molecular Sequence Data; D006517:Murine hepatitis virus / Q000235:genetics / Q000378:metabolism*; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; D014760:Viral Fusion Proteins / Q000378:metabolism*; D014763:Viral Matrix Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
D008562:Membrane Glycoproteins; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; D014760:Viral Fusion Proteins; D014763:Viral Matrix Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus