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gold cores resulted in larger structures (Sun
., 2007). Two-dimensional
crystals were grown for single particle analysis using transmission
electron microscopy (TEM) and 3D image reconstruction. VLPs with 6 nm-
sized cores yielded particles with
et al
1 symmetry, VLPs with cores of
9 nm-sized cores gave VLPs resembling
T =
2 symmetry, and the
aforementioned VLPs containing cores with a diameter of 12 nm showed
T =
pseudo
T =
3 symmetry (Fig. 5.9) (Sun
et al
., 2007). Native BMV particles with
T =
1,
pseudo
T
= 2, and
T =
3
symmetry have also been isolated (Krol
et al
., 1999;
Lucas
et al
., 2001).
Figure 5.9
Panel A: Negative-stain electron micrographs, Fourier transforms
(inserts), and corresponding Fourier projection maps. (a) BMV 2D crystal. The
lattice constant is 26 nm (one unit cell is drawn), and the arrangement of the
densities suggests a
= 3 structure. (b) VLPs containing 12 nm-sized gold cores
arranged in a 2D lattice. The lattice constant is 25 nm. Panel B: 3D reconstructions
of BMV and VLP using negative stain data. (a)
T
T =
1, 2, and 3 models of BMV
capsids. The
= 2 structures were obtained from the Virus
Particle ExplorR (VIPER) database. The
T
= 1 and pseudo
T
= 3 structure is the reconstructed image
of BMV in this work (Scale bar, 210 Å.) (b) VLPs containing 6 nm-sized gold cores
are characterized by the absence of electron density at the threefold symmetry axes.
Its structure and diameter bring it close to a
T
= 1 capsid. (c) The VLPs containing
9 nm-sized gold cores are reminiscent of a pseudo
T
= 2. The presence of electron
density at the threefold axes distinguishes it from the VLP structure with 6 nm-
sized cores. (d) The shape of the VLPs containing 12 nm-sized gold cores resembles
more the spherical shape of BMV, although it still lacks clear evidence of hexameric
capsomers. Concentric layering is a characteristic of all VLPs. Reproduced with
permission from Sun, J., DuFort, C., Daniel, M. C., Murali, A., Chen, C., Gopinath, K.,
Stein, B., De, M., Rotello, V. M., Holzenburg, A., Kao, C. C., and Dragnea, B. (2007)
Core-controlled polymorphism in virus-like particles,
T
Proc. Natl. Acad. Sci. USA,
104
(4), 1354-1359.
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