Elastic properties of viruses

Abstract

Viruses are compact biological nanoparticles whose elastic and dynamical properties are hardly known. Inelastic (Brillouin) light scattering was used to characterize these properties, from microcrystals of the Satellite Tobacco Mosaic Virus, a nearly spherical plant virus of 17-nm diameter. Longitudinal sound velocities in wet and dry Satellite Tobacco Mosaic Virus crystals were determined and compared to that of the well-known protein crystal, lysozyme. Localized vibrational modes of the viral particles (i.e., particle modes) were sought in the relevant frequency ranges, as derived assuming the viruses as full free nanospheres. Despite very favorable conditions, regarding virus concentration and expected low damping in dry microcrystals, no firm evidence of virus particle modes could be detected.

FIGURE 1

AFM picture from the surface of a dry STMV microcrystal. The size of the STMV particles determined from the peak-to-peak height profile is ∼17 nm. Larger globules, possibly corresponding to aggregates of several virions, are also observed. The AFM measurements were made in tapping mode, at the frequency of 290 kHz, using a 15-nm silicon tip.

FIGURE 2

Polarized Brillouin spectrum of a wet STMV crystal in backscattering geometry (solid line). The Brillouin spectrum of a wet lysozyme crystal is shown for comparison (dashed line). The sharp lines at ±8 GHz arise from the surrounding aqueous buffer.

FIGURE 3

Polarized Brillouin spectrum of an air-dried STMV crystal in backscattering geometry (solid line). For comparison, the Brillouin spectrum of the wet crystal (Fig. 2) is also shown (dashed line).

FIGURE 4

Large frequency range spectra (solid lines, polarized; dashed lines, depolarized) of (a) a wet STMV crystal and (b) a dry STMV crystal. For clarity, only the Stokes side of the spectra are shown. The sharp peak at ∼30 GHz arises from the glass capillary.