The
BNoV RdRp gene contains highly conserved regions. VP1 is
the major structural component of caliciviruses and is involved in
receptor recognition, host specificity, strain antigenic diversity, and
immunogenicity (Chen et al., 2004). VP2 is highly variable and
can contain different types of mutations (Bok et al., 2009;
Seah,Gunesekere,Marshall, & Wright, 1999). VP2 interacts withVP1 and, in turn, enhances the expression of capsid proteins
(Vongpunsawad,Venkataram, & Estes, 2013). Due to the slightly different
topologies between ORF2 and ORF3, different BNoV VP2 gene may have
resulted from distinct evolutionary strategies (Kamel et al., 2009).
Phylogenetic trees were constructed based on the BNoV VP1 andRdRp genes (Figure 2). The strain isolated in the present study
and CH-HNSC-2018 were clustered in one branch, while strains isolated
from Sichuan, southern China, were clustered in another branch,
indicating that the BNoV strains in China are diverse. Different strains
with different genotypes exist in China, making the prevention and
control of viral spread difficult (Figure 2a). The sequence and
phylogenetic analyses showed that Bo/CH/HB/BD/2019 belongs to GIII.2
BNoV (Figure 2b).
The VP1 protein includes a shell (S) domain, which is highly
conserved among different NoVs, and a protruding (P) domain, with
N-terminal P1 and C-terminal P1 and P2 parts (Chen et al., 2013). The
highly variable region of the sequence (residues 279–406) forms the
externally located P2 subdomain, whereas the central subdomain P1
(residues 226–278 and the C-terminal 124 residues) is located between
the S and P2 domains (Venkataram,Hardy, & Estes, 2000). Comparing with
previous studies, in both China and other countries, we found four new
aa substitutions in VP1 , i.e., 225C, 246T, 624T, and 945T. The
225C residue is located in the conserved region and 246T is located in
the P1 subdomain in the highly variable region. This may be an
adaptation that is unique to BNoV circulating in cattle farms in Hebei,
China. Whether these mutations in Bo/CH/HB/BD/2019 lead to changes in
virulence, pathogenicity, and antigenicity remains to be explored.
In conclusion, in this study we isolated the Bo/CH/HB/BD/2019 strain
from Hebei, sequenced its genome, and identified its genes. We analyzed
its sequence homology with other BNoV strains and constructed
phylogenetic trees to analyze its genetic evolution. Our results provide
a reference for the development of a BNoV vaccine to prevent and control
viral spread. Nevertheless, more data are still required, so in the
future it will be necessary to further monitor and research BNoV and its
subtypes.