R. Gajardo et al., 2 PROLINE RESIDUES ARE ESSENTIAL IN THE CALCIUM-BINDING ACTIVITY OF ROTAVIRUS VP7 OUTER CAPSID PROTEIN, Journal of virology, 71(3), 1997, pp. 2211-2216
Rotavirus maturation and stability of the outer capsid are calcium-dep
endent processes. It has been shown previously that the concentration
of Ca2+-solubilizing outer capsid proteins from rotavirus particles is
dependent on the virus strain. This property of viral particles has b
een associated with the gene coding for VP7 (gene 9), In this study th
e correlation between VP7 and resistance to low [Ca2+] was confirmed b
y analyzing the origin of gene 9 from reassortant viruses prepared und
er the selective pressure of low [Ca2+]. After chemical mutagenesis, w
e selected mutant viruses of the bovine strain RF that are more resist
ant to low [Ca2+]. The genes coding for the VP7 proteins of these inde
pendent mutants have been sequenced. Sequence analysis confirmed that
these mutants are independent and revealed that an mutant VP7 proteins
have proline 75 changed to leucine and have an outer capsid that solu
bilized at low [Ca2+]. The mutation of proline 279 to serine is found
in all but two mutants, The phenotype of mutants having a single proli
ne change can be distinguished from the phenotype of mutants having tw
o proline changes. Sequence analysis showed that position 75 is in a r
egion (amino acids 65 to 78) of great variability and that proline 75
is present in most of the bovine strains, In contrast proline 279 is i
n a conserved region and is conserved in all the VP7 sequences in data
banks. This region is rich in oxygenated residues that are correctly
allocated in the metal-coordinating positions of the Ca2+-binding EF-h
and structure pattern, suggesting that this region is important in the
Ca2+ binding of VP7.