An amino acid in the heptad repeat 1 domain is important for the haemagglutinin-neuraminidase-independent fusing activity of simian virus 5 fusion protein
M. Ito et al., An amino acid in the heptad repeat 1 domain is important for the haemagglutinin-neuraminidase-independent fusing activity of simian virus 5 fusion protein, J GEN VIROL, 81, 2000, pp. 719-727
A canine isolate (strain T1) of simian virus 5 (SV-5) performed multiple re
plication in BHK cells but did not induce cell fusion for up to 3 days. In
contrast, a prototype strain (WR) provoked extensive cell fusion within 2 d
ays during the course of its replication. Accordingly, the fusion (F) prote
in of the T1 strain did not cause cell fusion even when co-expressed with t
he SV-5 haemagglutinin-neuraminidase (HN) protein, whereas the WR F protein
induced cell fusion in the presence of the HN protein. Differences in the
predicted amino acid sequences of the T1 and WR F proteins were found at 12
positions and it was proved that the T1 F protein had a longer cytoplasmic
tail than the WR F protein. By reducing the length of the cytoplasmic tail
or by replacing the tail with the WR F counterpart, the T1 F protein partl
y restored its HN-dependent fusing activity. Chimeric and mutational analys
es between the T1 F protein and the mutant F protein (L22P) suggested that
Glu-1 32 in the heptad repeat 1 domain was involved in the HN-independent f
using activity in addition to the previously identified Pro-22 at the F-2 N
terminus. It was also shown that Ala-290 in the heptad repeat 3 domain con
tributed to the HN-independent fusing activity to some extent.