Biology Reference
In-Depth Information
Particle production can be achieved in natural hosts, black-eyed peas
(in Latin
), or heterologous expression systems. In the
natural host, high titers of VNPs accumulate and 1-2 g can be isolated from
1 kg of infected leaf material. Heterologous expression systems give rise
to comparably high yields; for example, expression of CCMV VLPs in yeast
(
Vigna unguiculata
Pichia pastoris
) yields up to 0.5 g VLPs per kg wet cell mass(Brumfield
et
al
., 2004). Further coat protein monomers can be expressed in
Escherichia
coli
and then be self-assembled
in vitro
into intact empty CCMV protein cages
(Zhao
., 1995).
The structural transitions of CCMV.
et al
CCMV particles are highly dynamic
platforms. CCMV particles undergo reversible pH- and metal ion-dependent
structural transitions. These structural transitions are described as a
swelling mechanism, which results in an approximately 10% increase in the
particle dimension. The structural transition is a result of an expansion of
the threefold axis of the virus particle, and the swelling is accompanied by
the formation of 60 separate 2-nm-sized openings in the protein shell. Under
swollen condition these openings allow free molecular exchange between the
virus cavity and the surrounding bulk medium (Fig. 2.9) (Liepold
et al
., 2005;
Speir
et al
., 1995).
Figure 2.9
Cryo-electron microscopy and image reconstruction of
Cowpea chlorotic
mottle virus
. “Closed” conformation (pH
6.5, metal ions) (on the left), and “open”
conformation (pH
Reproduced with
permission from Liepold, L. O., Revis, J., Allen, M., Oltrogge, L., Young, M., and Douglas,
T. (2005) Structural transitions in
6.5, no metal ions present)
(on the right) .
Cowpea chlorotic mottle virus
(CCMV),
Phys
.
Biol
.,
2
(4), 166-172.
The dynamics and reversible swelling of the CCMV capsid have been
exploited for nanotechnology and is also referred to as
gating
. In the
 
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