Biology Reference
In-Depth Information
Virus-receptor
binding
Removal of S1
Insertion of fusion
peptide
Virus
S2
S1
Receptor
Cell
Conformational changes
of S protein
Fusion
Fig. 3.
Entry mechanism of coronaviruses. The entry mechanism of
MHV is very similar to that of HIV. MHV S protein binds its receptor
CEACAM1, and then S1 is removed from the envelope-anchored S2
subunit. Fusion peptide is inserted into the plasma membrane. These events
trigger conformational changes of the S2 to form 6 helix bundles consist-
ing of trimeric coiled coil HR1, over which 3 copies of HR2 bind. The fuso-
genic activation of SARS-CoV S protein is supposedly conducted by cellular
proteases, most likely cathepsin L, although a detailed mechanism of this
activation is not yet understood. Viral and cell membrane fusion is carried
out in a similar fashion to that of HIV and MHV, since 6 helix bundles were
shown to be formed.
Gallagher and his colleagues as a spread of JHMV infection — from cells
initially infected in a receptor-mediated fashion — to those cells lacking
the MHV receptor CEACAM1.
50
They showed this phenomenon by
overlaying JHMV-infected cells onto a CEACAM1 negative cell mono-
layer. Its S protein is responsible for this infection.
50
The mechanism of
receptor-independent infection is thought to be due to a unique feature
of the JHMV S protein. As described above, the S1 subunit of MHV is
removed from S2 after binding its receptor; S1 and S2 are not cova-
lently linked and thus S1 is physically removed from S2 under certain
