Human Rhinovirus Cell Entry and Uncoating - Structure-Based Study of Viral Replication - page 21

in the release of some viral proteins from the capsid and, with the aid of
the co-receptor ( β 5 -integrins), in rupture of the endosomal

membrane. However, endosome lysis by adenovirus does not require
low endosomal pH. 113 Upon endosome rupture, modified viral parti-
cles, together with the endosomal content, are delivered into the cyto-
plasm. The modified virions are then transported along microtubules to
the nuclear pore complex, where uncoating takes place and the viral
DNA is imported into the nucleus. The second mechanism (Fig. 6B) is
assumed to account for uncoating and RNA translocation of poliovirus
(Pv), another member of the picornavirus family, based primarily on
in vitro structural and electrophysiological studies. 114-116 Similar to major
group HRV, the Pv receptor (Pvr) catalyzes the structural alteration to
135S particles for infection. Upon interaction of Pv with soluble Pvr,
the N-terminus of VP1 (a predicted amphipathic helix) is externalized.
Thus, five amphipathic N-terminal helices together with five copies of
VP4 might form the hypothetical channel in the target membrane
through which the RNA might be released into the cytoplasm. 117 This
view is supported by the recent cryo-EM image reconstruction of Pv
attached to the membrane via five copies of Pvr showing a perturbation
of the membrane just below the virus. 118 The importance of VP1 and
of distinct amino acid residues in VP4 together with the N-terminal
myristoyl-modification in uncoating was shown in vivo by using Pv
mutants. 114,119,120 Pv with a mutation in VP4 that prevented RNA deliv-
ery into the cytoplasm and thus infection failed to form ion channels in
artificial lipid bilayers. 114 However, the electrophysiological data do not
differentiate whether in vivo Pv RNA is transported through such a
channel across a cell membrane or whether the channel destabilizes the
membrane and results in cytoplasmic delivery of the viral RNA together
with the modified particles. In addition, it should be noted that the cel-
lular site of Pv structural alteration and uncoating is still elusive.

α v β 3 or

Analysis of the Mechanism of Viral Genome
Penetration into the Cytoplasm

We have recently established various assays to analyze and quantify the
mechanism of viral genome penetration into the cytoplasm in vivo as
well as in vitro . 113,121,122 The in vivo assay is based on the properties of