Biology Reference
In-Depth Information
Fig. 4.
(
a
) Under normal AFM scanning conditions, the center protein on
the PBCV-1 is visible within the 5-protein pentagon. (
b
) With increased tip
pressure, the center protein disappears, while the surrounding pentagon
stays in place. Upon lowering the tip pressure, the center protein reappears
(not shown). (
c
) Icosahedral structure of a wild type Ty3 VLP with icosahe-
dral overlay; pentagonal vertices are shown in grey and hexagonal vertices are
shown in black.
structural information had been reported. Wild-type Ty3 particles
range in diameter from 25 nm to 52 nm. This particle variability
precludes successful structural analyses by cryo-EM, which relies on
molecular averaging. AFM imaging of Ty3 VLPs demonstrates the
spherical shape of a vast majority of the Ty3 particles, as well as cap-
somere arrangements on their surfaces (Fig. 4c). Measurements of the
capsomere center-to-center distances of a large number Ty3 VLPs
yields an average distance of 11.4 nm, consistent with a T
7 icosa-
hedral triangulation number. Additionally, the number of hexameric
capsomeres lying between pentameric capsomeres, as illustrated in
Fig. 4c, is consistent with T
=
7 icosahedra are
non-centrosymmetric they can exist in two enantiomorphs,
d
and
l
.
From the height information preserved in the AFM images, further
analysis allowed assignment of the Ty3 VLPs to the T
=
7 as well. Since T
=
=
7
d
class.
Vaccinia Virus
AFM can provide important high-resolution structural information
on polymorphous asymmetric viruses, which are not amendable to
