Virus Structure and Collective Oscillations

Virus structure includes up to three major components: genetic material (either DNA or RNA), a protein coat which surrounds the genetic material, and a membrane (Figures 9.1 thru 9.3). One example of a viral protein coat is the cylindrical lattice similar to microtubule structure found in the tobacco mosaic virus, the first virus to be isolated (by Russian botanist Dimitri Ivanovski in the late 19th century). In adenoviruses, the protein coat is an icosahedron: a 20 sided polygon with 12 vertices. Influenza virus protein coats are spherical and may include outward extruding glycoproteins surrounded by lipid membranes. Another interesting viral structure is that of bacteriophages which actively inject their DNA into host bacterial cells. The bacteriophage looks somewhat like a nanoscale lunar lander and has an icosahedron head mounted by a collar onto a cylindrical tail which in turn is supported by a base plate which contacts a bacterial cell surface. Upon an appropriate stimulus, the bacteriophage virus protein coat undergoes a collective conformational event; contraction of the entire tail assembly results in the active injection of viral DNA through the bacterial cell wall and into the bacterial cell cytoplasm. This sequence of events requires a coordinated communication and active response and may be construed as a rudimentary intelligence.

Figure 9.2: Icosahedral structure of an adenovirus protein coat. By Paul Jablonka.

Figure 9.3: Longitudinal view of the DNA path in a tobacco mosaic virus structure. The path takes about 120 complete turns. By Paul Jablonka.

How do viruses perform cognitive acts such as sensing host cell surfaces and injecting into them their nucleic acids? One possibility is by perturbations of collective vibrations of their protein shells. Michels, Schulz, Witz, Pfieffer, and Hirth (1979) measured ultrasonic absorption of protein assemblies over a range of 105 to 109 oscillations per second. They found the assembled structures absorb much greater ultrasonic energy than do the individual unpolymerized subunits, suggesting a collective oscillation of the protein assembly. For example, the intact icosahedral Brome mosaic virus absorbed energy with a mean frequency of 5 x 107 per second. Robach, Michels, Cerf, Braunwald and Tripier-Darcy (1983) found similar results with frog virus, and determined that the displacement amplitude of the oscillations were on the order of a tenth nanometer. Most virus research has focused on the genetic capabilities of viral DNA or RNA in coopting host cell activities. The protein coats have been considered as simple environments for DNA or RNA transport, however they perform functions analogous to organized cytoplasm. For example, the glycoprotein spikes which extend outward from some viruses while remaining anchored to the protein coat interact with the host membrane and cell wall surfaces to facilitate contact and entry. This general activity involves information signaled through the protein coat enacting a mechanical conformational change. Michels, Dormoy, Cerf and Schulz (1985) used similar techniques to study two strains of tobacco mosaic virus as well as other protein assemblies including microtubules. They observed that the fluctuations depend on specific organization and complexity of the assembly, and that certain assemblies oscillate more than others. They speculate that collective oscillations of virus coats could function in communicative functions such as the injection of viral nucleic acids into host cells. Viruses perform limited functions devoted to their own replication and survival, but their collective oscillations could be a clue to the essence of living matter. Collective oscillations of cytoskeletal proteins could serve a more versatile communicative role in all eukaryotic cells.

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