Tobacco mosaic virus, 1st of April 2012.
Viruses which I thus far shown on the pages of "Construction of Reality" were spherical or icosahedral viruses.
This means that their symmetry was based on icosahedral group which can be represented with 60 matrix transformations.
Although the icosahedral viruses are the most common among the viruses discovered thus far, there are other types. Perhaps the
best known among them is the HIV virus which looks like a short baseball bat, i.e. like a two "half"spheres connected with a
conical surface.
The first ever discovered virus is also not icosahedral - it is cylindrical. This is a tobacco mosaic virus (TMV). This virus is a
subject of this post and it is shown on all the images in it.
One could say that TMV virus was discovered by Wendell Meredith Stanley who first crystalized it in year 1935.
On the image which opened this post virus proteins are shown in red-orange hues, and their color depends on the distance from the
virus axis. Virus RNA molecule is shown in the blue-cyan hues. It is interesting that the biggest part of the virus RNA molecule is
not situated in the cylindrical hole of the virus, but tightly packed between virus proteins, as the image above shows.
The structure of TMV virus is helical, and one periodic unit (a turn, a screw) contains 16.3 protein units and a height of 2.3 nm (see the image above). This structure is a simple variant of structures I discussed in a post >> Lake structures and on which I published a paper entitled >> Coating carbon nanotubes: Geometry of incommensurate long-range-ordered physisorbed monolayers. In the classification described in this work, the TMV virus would be a structure of (16,1) type.
In the context of my research work, TMV virus is especially important because this was the first virus which was experimentally
demonstrated to self-assemble, i.e. that it can be spontaneously assembled from dis-assembled individual proteins and its ssRNA
molecule. This was first shown by >> Heinz Fraenkel-Conrat and
>> Robley Williams, and here is what
>> the article in Wikipedia says about it: In 1955, Heinz
Fraenkel-Conrat and Robley Williams showed that purified TMV RNA and its capsid (coat) protein assemble by themselves to
functional viruses, indicating that this is the most stable structure (the one with the lowest free energy).
In any case, the proof of self-assembly is important because it enables us to view the virus as a structure that belongs to
the realm of physics, perhaps even more than to the realm of biology. This is corroborated by the career of Robley Williams
who got his PhD in physics, he was an associate professor of astronomy at the University of Michigan, and then he became
professor on the newly opened Department for virology at the University of California, Berkeley in year 1950. He was invited to
California by Wendell Stanely.
The virus contains 2130 copies of the coat protein and is thus about 300 nm long (2130 / 16.3 * 2.3 nm = 300 nm).
Virus RNA contains about 6400 bases (about 3 per virus protein - monomer).
Today, it is exactly three years since I last ignited the tobacco roll.
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Last updated on 1st of April 2012.