Biology Reference
In-Depth Information
proteins of vaccinia virus are all considerably less,
23
the subunits prob-
ably represent oligomers.
AFM allows direct visualization of the structural dynamics of
viruses in response to changes in their environment. In this particular
case, AFM allows imaging of IMV particles in both water and air.
Thus, as illustrated in Fig. 5b, upon dehydration air-dried vaccinia viri-
ons assumed more rectilinear shapes with relatively uniform dimen-
sions of 300-360
120-130 nm (height),
representing a reversible 2.2-2.5-fold shrinkage. This shrinkage is
accompanied by topological and topographical changes resulting in
“brick-shaped” morphologies similar to those observed in EM images.
The dried virions have a pronounced, raised area in their center, which
extends approximately 30 nm above the virion surface. Thus, AFM
observations directly demonstrate that conventional EM images
shown in literature that purported to show native vaccinia virion struc-
ture were fraught with drying artifacts. AFM also demonstrates the
remarkably deformable, fluid nature of the virion structure, which
allows a ~2.5-fold collapse along the vertical dimension upon drying.
×
240-280 nm (lateral)
×
Visualization of Subviral Structures
In the previous sections we described applications of AFM for probing
the high-resolution structures of the virions' outer surfaces. In addi-
tion, AFM can be utilized to probe their internal structural features.
This can be accomplished through a controlled dissection of viruses
with chemical agents or enzymes, resulting in the sequential peeling
away of layers of structure. Newly revealed/exposed structural layers
can then be imaged by AFM.
Herpes Virus
The ability to utilize AFM for imaging of subviral structures was first
demonstrated in the visualization of herpes simplex virus-1.
5
The
outer layer of the HSV-1 virus is formed by an oversized lipid enve-
lope (Fig. 5c). Inside is the actual capsid, as well as the tegument, a
varied collection of proteins present between envelope and capsid.
