Protein of the Year: Tobacco Mosaic Virus

Source:  Protein of the Year: Tobacco Mosaic Virus    Tag:  tobacco mosaic virus replication
The tobacco mosaic virus was in fact the very first to be discovered. An infectious agent far too small to be bacteria was found to be causing disease in the tobacco crop in the late 1800s. It was a lot of research and 30 years later that the composition of the agent was found to be primarily protein, with a bit of RNA. The structure of TMV was soon to follow, revealing the protein coat discussed in Post 1. Though the coat is very useful in protecting the viral RNA from destructive enzymes, it poses a problem once the virus is inside the cell; it must be removed in order to replicate the RNA. This is solved by the different environments inside and outside of the host cell. There are several amino acid clusters in the protein coat that are stable in a calcium-rich environment, like outside of the cell. Once inside the cell, the lower calcium levels cause the amino acids to repel each other. This loosens the first few proteins, releasing the end of the RNA. The host cell's ribosomes are utilized to code the RNA, and as the ribosome moves down the RNA, it displaces the remainder of the protein coat.
Four genes are encoded by the viral RNA; two replicase-associated proteins that help to replicate the rest of the RNA, a movement protein that facilitates the spread of the RNA from cell to cell, and the very same protein coat that protects the RNA.


The virus can infect over 150 plants including tobacco, tomatoes, peppers, and cucumbers, and is transmissible through mere contact. This is particularly problematic because the virus is so stable that it can survive for years in a considerable range of pH and up to 95 degrees Celsius. There is also no efficient chemical treatment available to protect plants from infection.
Though TMV cannot replicate or cause disease in humans or other animals, its presence does induce TMV-antibody formation. The most common way of contact a person would have to TMV is by smoking or chewing tobacco, since the virus can live in infected leaves for years.
Smokers are statistically less likely to develop Parkinson's disease, and a 2013 study may have shown why that is. A smoker may have been exposed to TMV at some point, inducing the production of TMV-antibodies. Interestingly, this study found that TMV has a similar sequence to a polymorphism of a protein that is associated with Parkinsons; so similar that the TMV-antibodies will recognize this polymorphism and attack it. This is a field in which pursuing TMV could be an enormous breakthrough.


References:
Liu, Ningning, Ying Chen, Bo Peng, Yuan Lin, and Qian Wang. "Single-Molecule Force Spectroscopy Study on the Mechanism of RNA Disassembly in Tobacco Mosaic Virus."  Biophysics Journal  105.12 (2013).  PubMed . Web. 6 Mar. 2015.

Liu, Ruolan, Radhika A. Vaishnav, Andrew M. Roberts, and Robert P. Friedland. "Humans Have Antibodies against a Plant Virus: Evidence from Tobacco Mosaic Virus."  PLoS One  8.4 (2013).  PubMed . Web. 6 Mar. 2015.

Scholthof, . "Tobacco mosaic virus."  American Phytopathological Society . American Phytopathological Society, 2005. Web. 6 Mar. 2015.

Goodsell, David. "Tobacco Mosaic Virus."  Protein Data Bank . RCSB, Jan. 2009. Web. 6 Mar. 2015.