Biology Reference
In-Depth Information
VP2 and VP3
The highly basic VP2 may serve a function similar to the basic N ter-
minus of plant virus capsid proteins, which are involved in RNA bind-
ing, since the N terminus of NoV VP1 is acidic and is not thought to
interact directly with the viral genome.
6
However, VP2 is not essen-
tial for the expression of VLPs,
35
but may serve a regulatory function.
This is thought to confer stability to the capsid protein.
6
This protein
is believed to be associated with encapsulation of the genomic RNA.
The function(s) of the VP3 is unknown and is only found in SaV GI,
GIV, and GV strains.
Antigenicity
Expression of VP1 results in the formation of VLPs that are morpho-
logically and antigenically similar to native viruses.
11
At least two kinds
of assays have been used to examine the cross-reactivities among these
VLPs, an antibody enzyme-linked immunosorbent assay (ELISA) and
an antigen ELISA.
9,36-39
The antibody ELISA is broadly reactive,
whereas the antigen ELISA is specific, only detecting strains that are
closely related (>95% identity in the RNA polymerase region). For
example, in an antibody ELISA, NoV GI/11 antiserum showed broad-
range cross-reactivities, detecting 2 NoV GI and 10 GII genotypes.
35
Likewise, NoV GII/1, GII/10, and GII/12 antisera also showed
broad-range cross-reactivities in a antibody ELISA, detecting several
other distinct NoV GII genotypes.
35
Amino acid alignment of NoV
VP1 suggested that these broad-range cross-reactivities were due to
conserved amino acid residues located within the shell and/or P1-1
domains. On the other hand, unusual cross-reactivities among different
GII/3 antisera were observed in an antibody ELISA. The four kinds of
GII/3 antisera (strains 809, Sh5, 18-3, and 336) cross-reacted moder-
ately to weakly against GII/3 1152 VLPs (i.e. up to eight-fold lower
than homologous VLP titer). Amino acid alignments of these five
GII/3 sequences revealed 1152 had three unique amino acid residues
compared to the other four GII/3 sequences (amino acid positions
Thr-285, Ile-372, and Ser-508), two of which were located within the
P2 domain (Thr-285 and Ile-372). Amino acid secondary structure
