Mosaic Virus Particle

Assembly and Stability of the Tobacco Mosaic Virus Particle D. L. D. Caspar... 

Figure 4.21 Effect of axial ratio and particle concentration on relative viscosity. Data are for tobacco mosaic virus particles. Adapted from M. A. Lauffer, 7. Am. Chem. Soc., 66, 1188. Copyright 1944 by The American Chemical Society, Inc.

The ratio (a/b), called the axial ratio of the ellipsoid, is frequently used as a measure of the deviation from sphericity of a particle. It plays an important role, for example, in our discussions of sedimentation and viscosity in Chapters 2 and 4, respectively. In the event that a > b, the prolate ellipsoid approximates a cylinder and, as such, is often used to describe rod-shaped particles such as the tobacco mosaic virus particles shown in Figure 1.12a. Likewise, if a < b, the oblate ellipsoid approaches the shape of a disk. Thus, even the irregular clay platelets of Figure 1.12b may be approximated as oblate ellipsoids. 

FIG. 1.12 Electron micrograph of two different types of particles that represent extreme variations from spherical particles (a) tobacco mosaic virus particles (Photograph courtesy of Carl Zeiss, Inc., New York) and (b) clay particles (sodium kaolinite) of mean diameter 0.2 fim (by matching circular fields). In both (a) and (b), contrast has been enhanced by shadow casting (see Section 1.6a.2a and Figure 1.21). (Adapted from M. D. Luh and R. A. Bader, J. Colloid Interface Sci. 33, 539(1970). 

Figure 4.12a shows plots of the intrinsic viscosity —in volume fraction units —as a function of axial ratio according to the Simha equation. Figure 4.12b shows some experimental results obtained for tobacco mosaic virus particles. These particles —an electron micrograph of which is shown in Figure 1.12a—can be approximated as prolate ellipsoids. Intrinsic viscosities are given by the slopes of Figure 4.12b, and the parameters on the curves are axial ratios determined by the Simha equation. Thus we see that particle asymmetry can also be quantified from intrinsic viscosity measurements for unsolvated particles. 

S-TT Klug, A., The tobacco mosaic virus particle structure and assembly , Phil. Trans. RoyalSoc. Ser. B, Biol. Scl. 1999, 354, 531-535. 

Figure 9.2 Transmission electron micrograph of Cowpea mosaic virus particles negatively stained with uranyl acetate. The scale bar is lOOnm.

Stubbs, G. (1999). Tobacco mosaic virus particle structure and the initiation of disassembly. Philos. Trans. R. Soc. Lond. B Biol. Sci. 354, 551-557. 

The Size and Shape of Tobacco Mosaic Virus Particles. J. Amer. chem. 

Figure 1.3.3 Electron micrograph of tobacco mosaic virus particle. [Courtesy of Prof. Emeritus Robley C. Williams, Virus Laboratory and Dept, of Molecular Biology, Univ. of California, Berkeley.]...

Figure 3. Transmission electron microscopy of enzyme-cleaved, tobacco mosaic virus particles on the apex of a tungsten field-emitter tip (imaged at 200kV). TMV sample kindly supplied by P. J. Butler, the MRC, Cambridge, England.

Destito G, Yeh R, Rae CS, Finn MG, Manchester M. Folic acid-mediated targeting of cowpea mosaic virus particles to tumor cells. Chem Biol 2007 14 1152-1162. 

Kuznetsov, Y. G., Larson, S. B., Day, J., Greenwood, A., and McPherson, A. 2001. Structural transitions of satellite tobacco mosaic virus particles. Virology 284,223-234. 

Klug, A. The tobacco mosaic virus particle Structure and... 

Scheme 70 A Labeling of azide-modified cowpea mosaic virus particles 329 and 330 with alkyne-derivatized fluoresceine 334, B labeling of alkyne-modified cowpea mosaic virus particles 332 with azide-derivatized fluoresceine 335 [60]...

Each tobacco mosaic virus particle consists of one long thread of nucleic acid embedded in protein. The protein surrounds the nucleic acid in loops or in the fashion of screw threads making up the super-molecule. Treatment with phenol separates nucleic acids from protein. The nucleic acid obtained in this mild way remains infectious, and in a host cell can cause virus multiplication and consequent symptoms of disease. About 95% of the material is protein it consists of individual subunits with a molecular weight of 17,500, which exhibit a marked tendency to aggregate At neutral or slightly acidic pH the protein molecules aggregiite to little rozls, very similar to the intact virus particles both in shape and size. The amino acid sequence is now known. Mutants obtained by nitrous acid treatment (see above) show up differences in the amino acid sequence usually only one amino acid has been replaced, for example, serine by leucine, or leucine by phenylalanine. 

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