Biology Reference
In-Depth Information
Bromovirus
family, Fig. 2b) shows them to be strikingly different. In
BMV the capsomeres are wide and have crown-like structures, while
those in TYMV are close and dense. Further inspection indicates ~25 Å
holes at the centers of BMV capsomeres (Fig. 2b) consistent with the
structure of BMV based on X-ray diffraction analysis.
10
This demon-
strates that imaging at a lateral resolution of ~20 Å is possible on
viruses,
in vitro
.
Herpes Simplex Virus-1
The clarity with which structural detail can be recorded on the
surfaces of small T
3 plant viruses suggested that AFM may be even
more broadly useful as an analytical tool for macromolecular struc-
tural investigations and may provide important topographical infor-
mation on large animal and human viruses. Thus the capabilities of
AFM in structural studies of human viruses may be illustrated by
our work
5
on the visualization of the icosahedral capsid of herpes
simplex virus-1 (HSV-1). The structure of the icosahedral capsid of
HSV-1, which was deduced by cryo-EM to 8.5 Å,
11
provides a
standard against which the AFM images can be compared. The main
components of the 125 nm T
=
16 icosahedral HSV-1 virion are
12 pentameric capsomeres and 150 hexameric capsomeres. These cap-
someres are interconnected by 320 smaller protein complexes known
as triplexes.
11
As illustrated in Fig. 3a, the capsomere structure of the HSV-1
capsid could be visualized by AFM even at relatively low magnifica-
tion, with the capsomere size of ~15 nm being accurately reflected. At
higher resolution, the protein clusters that link adjacent capsomeres
and the substructure of individual capsomeres could be further visu-
alized (Fig. 3b). The 4-5 nm clusters between capsomeres correspond
to triplexes that are a characteristic feature of the capsid. Furthermore,
many capsomeres show a ~35 Å hole in their center, which is consis-
tent with the cryo-EM reconstruction model of the HSV-1 capsid.
Furthermore, while the overall structure of capsids seen in AFM
images resembles the cryo-EM reconstruction model, natural varia-
tions of the mean structure were observed as well. AFM images of
=
