Biology Reference
In-Depth Information
Mixing of a virus solution with detergent (0.2% Triton X-100) results
in the removal of the lipid envelope from intact virions, which then
renders the underlying tegument and capsomere structure visible
(Fig. 5d). On the upper part of the capsid the underlying, highly reg-
ular capsomere packing can be recognized, while its lower part is
covered with an irregular coating of particles of up to 10 nm. This
~10 nm size corresponds well with an MW of 336 kDa of the largest
protein VP 1-3 present in the tegument. More vigorous treatment
of virions with detergent results in the loss of all envelope and tegu-
ment, revealing the complete icosahedral capsid structure as seen in
Figs. 3a and 3b.
AFM can probe not only the structures of large macromolecular
assemblies, but also their dynamic processes. For example, the disassem-
bly of virions and the release of HSV DNA were observed as illustrated
in Fig. 5e. Here, the treatment of HSV-1 virions with 0.5% sodium
dodecyl sulfate resulted in the emergence of DNA in the form of bun-
dles of many intertwined DNA chains. Individual DNA fibers were
found to have diameters of 1.5-3 nm, which corresponds well to the
2.5 nm diameter of a double-stranded DNA double helix. In the inset of
Fig. 5e entire capsomeres are seen to be lost from the capsid surface, and
an individual double-stranded DNA chain emerges from the capsid.
Vaccinia Virus
In the case of vaccinia virus the internal virion structures were revealed
through the subsequent treatment of virions with sets of chemicals
and/or enzymes.
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Consecutive subviral structures including core
envelopes, viral cores, and nucleoprotein filaments, as well as viral DNA,
were visualized (Fig. 6). Note that the “studs” seen in Fig. 6a on the
enveloping membrane surface have the same size as the protru-
sions on the surfaces of untreated IMV (Fig. 1d). Membrane patches
varied in thickness from 25 nm to 35 nm and were ~700
×
900 nm in
surface area.
The heights of the viral cores seen in Fig. 6b are in the range of
170-220 nm, which is roughly the height of the intact IMV virion
