Biology Reference
In-Depth Information
S1
S2
SS
HR2
TM
HR1
S1N330
1-330
ca.160 aa
MHV
FP
SARS-
CoV
318-510
1-250
400-550
TGEV
receptor-binding site
SS: signal sequence
FP: fusion peptide
hypervariable region
TM: transmembrane domain
Fig. 1.
Structural comparison of different coronavirus S proteins. Coronavirus
S protein is a class I fusion protein, which is similar to the influenza HA and HIV
gp 160 envelope protein. The MHV S protein is cleaved in the middle of the
molecule, resulting in N terminal S1 and C terminal S2 subunits, while the
SARS-CoV S protein is not cleaved. The N terminal region of S1, consisting of
330 residues (S1N330), is a receptor-binding site for MHV, whereas the inter-
nal region from residues 318 to 510 is responsible for receptor binding of SARS-
CoV S protein. Downstream from the S1N330 exists a hypervariable region
consisting of ~160 residues, whereas various deletions exist in N terminal region
consisting of ca. 250 residues of porcine transmissible gastroenteritis virus
(TGEV) S protein. In S2, there are two heptad repeats, HR1 and HR2, that play
critical roles in viral envelope-cell membrane fusion. Fusion peptide is located
close upstream of HR1 in SARS-CoV S protein; however, the MHV S protein
fusion peptide is located elsewhere in an internal, as yet unidentified, region of
S2. The S protein of SARS-CoV is more similar to the TGEV S protein than to
MHV S in terms of the cleavability and localization of the receptor-binding site.
when comparison is made among the various MHV strains. The cleav-
age site consists of a basic amino acid cluster, which is recognized by cel-
lular proteases such as furin. The S1 fragment is believed to construct the
globular part of the spike and the S2 fragment its stem-like portion.
13
SARS-CoV S protein, however, is not cleaved (Fig. 1).
6,7
This feature of
uncleavability is similar to that of the S protein of the coronaviruses clas-
sified into group 1, such as porcine transmissible gastroenteritis virus
(TGEV) and feline infectious peritonitis virus (FIPV).
2
In the middle of
the SARS-CoV S protein, there are regions containing two basic amino
