Biology Reference
In-Depth Information
Many viruses have
T
= 3 icosahedral symmetry. These include
Brome
mosaic virus
(BMV),
Cowpea chlorotic mottle virus
(CCMV),
Hibiscus chlorotic
ringspot virus
(HCRSV),
Red clover necrotic mottle virus
(RCNMV),
Turnip
yellow mosaic virus
(TYMV),
Flock House virus
(FHV), MS2, and Q
b
. All of these
particles are formed by 180 identical coat protein subunits (60
subunits).
There is, however, a wide range; the capsid of P22 has icosahedral
T
T
= 4
symmetry, T7 and HK97 have
T
= 7 symmetry, and
Adenovirus
(Ad)
has
T
= 25
symmetry. The enveloped virus
= 4 symmetry.
The largest virus utilized for nanotechnology is the enveloped virus CIV,
and its capsids have
Rubella
has capsids of
T
T
= 147 symmetry. Structural information including
T
values can be found using the databases: VIPER; http://viperdb.scripps.
edu, and ICTV; http://www.ncbi.nlm.nih.gov/ICTVdb. To illustrate the
different symmetries cryo-electron microscopy reconstruction images of
CCMV, HK97, and Ads are given in Fig. 2.5. In theory, any size of icosahedron
can be formed. However, the largest isometric particle formed of a single
subunit type found in nature has
= 7 symmetry. If larger structures are
formed, the capsids appear to require one or more additional structural
scaffolding proteins that control and stabilize the self-assembly process
(Johnson & Speir, 1997). This is certainly the case for Ad
T
= 25), in
which the capsid is formed with 12 additional structural proteins (see
Section 2.2.12) (Rux & Burnett, 2004; San Martin & Burnett, 2003).
(
T
Figure 2.5
Cryo-electron microscopy reconstruction images of the mammalian
virus
Adenovirus
(Ad) (
T
= 25), the bacteriophage HK97 (
T
= 7), and the plant virus
Cowpea chlorotic mottle virus
= 3). The triangular coordinates are shown as black
triangles. Reproduced with permission from Johnson, J., Lin, T., and Lomonossoff, G.
(1997) Presentation of heterologous peptides on plant viruses: genetics, structure,
and function,.
(
T
Annu
.
Rev
.
Phytopathol
.,
35
, 67-86.
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