Biology Reference
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icosahedral twofold axes than at quasi-twofold axes in the cryoEM
map. The model suggests that the C terminus of the coat protein
of MGNNV is probably located at the outer surface of the capsid. In
contrast, the X-ray structures of insect nodaviruses showed that the
C-terminal regions are situated inside the capsid. Presumably, residues
around 216 form a polypeptide hinge to connect the two domains.
It is likely that the relative position and orientation of the outer
domain in MGNNV are different from those in TBSV. The protrud-
ing domains in MGNNV are held together around the quasi-threefold
axes to form 60 protrusions, whereas the protruding domains in TBSV
join at the icosahedral and quasi-twofold axes to form 90 protrusions.
VLPs Compete Against Infection by Native DGNNV
The surface properties of VLPs can be characterized by their ability to
compete with infection by the native virus. The first step of infection
is attachment to the cell membrane. CPE is then observed when the
virus multiplies in the host cells. As a viral structure analogue, VLPs
should be able to specifically occupy virus receptor sites and block
entry of the virus into the cell. Therefore, occurrence of CPE and
attachment to the cell surface were employed to test the structural
properties of the DGNNV VLPs. CPE resulting from native virus
infection was characterized by the formation of a vacuole in the cyto-
plasm and the disintegration of cells four days post-infection (p.i.).
6
In the presence of VLPs, cells were protected from invasion by the
virus and retained almost complete integrity at four days p.i. As
observed in a fluorescent microscope, the cell surface did not bind
FITC-labeled virus in the presence of VLPs, while FITC-labeled virus
and VLPs alone attached to the cell surface. These results suggest that
the VLPs formed in
E. coli
can bind to the surface protein of cell
membranes and block early virus-cell recognition and the effective
internalization of the virus. The virus receptor on the cell membrane
can specifically bind both native virus and VLPs. The outer shell of
DGNNV VLPs expressed in
E. coli
is thus structurally indistinguish-
able from native virus. To our knowledge, this is the first report that
the piscine nodavirus capsid protein can form VLPs in
E. coli
. The VLP
