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. 2009 Jan;96(1):9-20.
doi: 10.1529/biophysj.108.137489.

Size regulation of ss-RNA viruses

Roya Zandi  1 , Paul van der Schoot
Affiliations

Size regulation of ss-RNA viruses

Roya Zandi et al. Biophys J. 2009 Jan.

Abstract

While a monodisperse size distribution is common within one kind of spherical virus, the size of viral shells varies from one type of virus to another. In this article, we investigate the physical mechanisms underlying the size selection among spherical viruses. In particular, we study the effect of genome length and genome and protein concentrations on the size of spherical viral capsids in the absence of spontaneous curvature and bending energy. We find that the coat proteins could well adjust the size of the shell to the size of their genome, which in turn depends on the number of charges on it. Furthermore, we find that different stoichiometric mixtures of proteins and genome can produce virus particles of various sizes, consistent with in vitro experiments.

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Figures

Figure 1
Figure 1
Schematic view of a polymeric molecule inside a capsid. D indicates the thickness of the adsorbed layer, R the radius of the capsid.
Figure 2
Figure 2
Free energy per protein subunit fn scaled to its minimum value |f∗n| versus the capsid radius R in nanometers. The values of the combination of parameters (nMν/γb) for the corresponding optimal radius, Eq. 5, were chosen such as to obtain the radii corresponding to typical T = 4 and T = 7 viruses. We set the molecular weight corresponding to the dashed curve for the T = 4 structure 1.6 times higher than that of the solid curve for the T = 7 structure, while keeping all the other parameters constant.
Figure 3
Figure 3
Plotted is the scaled fraction of capsids xq/Xp versus the mole fraction of genome, Xg. The concentration of T = 4 structures (solid curve) increases while that of the T = 7 ones (dashed curve) decreases as the concentration of genome, Xg, increases. To calculate the curves, we set q1 = 42, q2 = 72, ɛq1 = −3 kBT, and ɛq2 = −3.075 kBT. The mole fraction of capsid proteins was fixed at Xp = 0.054.
Figure 4
Figure 4
The scaled fraction of capsids versus the mole fraction of genome. The concentration of T = 1 structures (solid line) increases faster than that of T = 3 (dashed curve) ones as the concentration of RNA increases. For the T = 1 structures, q1 = 12 and ɛq1 = −2 kBT. For the T = 3 structures, q2 = 32 and ɛq2 = −2.37 kBT. The number of encapsulated chains for the two T numbers was set to g1 = 1 and g2 = 2. The protein concentration was kept constant at Xp = 0.05.
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