Flock house virus

Fig. 6. The Flock House virus has an icosahedral symmetry with the y-peptide and the C and N termini of the /3-protein lying internally and away from the surface. However, time resolved proteolysis data indicates that the viral capsid is highly mobile and that internal domains are transiently exposed on the surface...

In terms of viral assembly and structure the baculovirus system has been used with tremendous success and some representative examples are discussed in more detail below. Generally speaking, the expressed viral protein (s) can be expected to assemble into particles that are structurally similar if not identical to their native counterparts. This has been shown specifically in the case of the nodavirus Flock House virus, where X-ray analysis of native virions and VLPs showed no differences in the structure of the protein capsid (V. Reddy and J. E. Johnson [The Scripps Research Institute, La JoUa, CA], unpublished data). Similarly, structural investigations at lower resolution, using cryoelectron microscopy and three-dimensional image reconstruction, have confirmed the identity of native and synthetic virions in many other cases. This feature combined with the large amounts that can be obtained has permitted structural analysis of many viruses for which only limited amounts of native virions were available. 

Bong, D. T., Steinem, C., Janshofif, A., Johnson, J. E., and Reza Ghadiri, M. (1999). A highly membrane-active peptide in flock house virus Implications for the mechanism of nodavirus infection. Chem. Biol. 6, 473 81. 

In the first studies, antibodies were used to elucidate the dynamic nature of poliovirus [51]. Antibodies were raised against peptides representing VP4 and the N termini of VPl. In the crystal structures of all of the picornaviruses, these termini lie at the capsid-RNA interface and are therefore not exposed to external solvent [27, 46, 52-55]. These antibodies bound to the virus when the particles were heated to 37°C but did not bind when added to virus at room temperature or when the virus was heated to 37°G and then cooled to room temperature. Therefore, although difficult to visualize with the static structure of the capsid, the only explanation for these results is that these buried termini are transiently exposed. This exposure is facilitated by higher temperatures and was proposed to be part of the normal infection process. This idea of dynamic capsid structures was subsequently supported by mass spectroscopy analysis of flock house virus [56] and rhinovirus [57] and by a series of drug—poliovirus structures [58]. 

Johnson, Fig. 3. A composite of the capsid of paricoto virus (a nodavirus related to flock house virus) produced by electron cryomicroscopy and the packaged nucleic acid produced from the X-ray structure. The regions of the capsid protein that interact with the RNA are also shown from the X-ray structure (Tang et al, 2001). 

Figure 10 Linear proportionality between the genome length and the net positive charge on all polypeptide tails in a capsid/ The generality of the result is borne out in many viruses, including satellite tobacco mosaic, hepatitis B, Flock house, and Sindbis viruses. The pictures of the vimses are from http // www.ICTVdb.org/...

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