Biology Reference
In-Depth Information
to its receptors on the HeLa cell surface and exposed to a pH 5.3 buffer
at 4
C, is entirely converted to C-antigen. These C-antigenic particles
are then gradually released from the plasma membrane. When cells
were subsequently warmed to 34
°
C after dissipation of the low endo-
somal pH by bafilomycin to inhibit any endosomal uncoating but to
permit virus replication, viral
de novo
synthesis was observed.
91
This
demonstrates that HRV2 uncoating and RNA transfer into the cytosol
can be artificially induced at the plasma membrane by exposure to low
pH. Apparently, the major group virus HRV14 fails to uncoat at the
plasma membrane at neutral pH given the lack of infection of HeLa
cells over-expressing non-functional mutant dynamin.
81
This is in agree-
ment with RNA penetration into the cytosol by rupture of a cellular
(endosomal) membrane, a process deleterious for the host cell when it
occurs at the plasma membrane.
°
Potential Mechanisms of RNA Egress
In cryo-EM pictures taken from HRV3-sICAM-1 complexes formed
at 4
C, the receptor is seen to remain
bound even after RNA egress.
101
The structural data derived from the
image analysis were interpreted as indicating that the breathing cap-
sid was held in an “open conformation” by the receptor acting like
a wedge. This is particularly visible at the star-shaped dome at the
five-fold axes that become enlarged and raise upward, resulting in an
overall increase in diameter of the particle by 4% and a loosening of
the inter-protomer contacts; the density at the pseudo-threefold axes
was interpreted as indicating the externalization of VP4 and of the
N-terminus of VP1 close to the ICAM-1 molecule, which would even
provide a hydrophobic residue for interaction.
The cryo-EM structure of empty HRV14 particles generated in the
absence of a receptor by heating to 55
°
C followed by heating to 37
°
C showed similar rearrange-
ments. However, the density was not increased at the pseudo three-fold
axes but rather at the five-fold axes, thereby suggesting exit of the VP1
N-terminus together with VP4 at this location.
99
The presence of VP4
is in agreement with biochemical data indicating that a large percent-
age of VP4 remained associated with subviral particles.
93
°
In both
