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Molecule of the Month: Tobacco Mosaic Virus

by PhilipJ on 8 January 2009


Tobacco mosaic virus (TMV) has been at the center of virus research since its discovery over a hundred years ago. TMV was the first virus to be discovered. Late in the 19th century, researchers found that a tiny infectious agent, too small to be a bacterium, was the cause of a disease of tobacco plants. It then took 30 years of work before the nature of this mysterious agent became apparent. In a Nobel-prize-winning study, Wendell Stanley coaxed the virus to form crystals, and discovered that it was composed primarily of protein. Others quickly discovered that there was also RNA in the virus. Then, many prominent structural researchers (including J. D. Bernal, Rosalind Franklin, Ken Holmes, Aaron Klug, Don Caspar, and Gerald Stubbs) used X-ray diffraction and electron microscopy to probe the structure of the virus.

Several structures of the whole tobacco mosaic virus are available in the PDB, including one solved by x-ray diffraction of fibrous crystals (shown here from PDB entry 2tmv) and a more recent structure solved by analysis of many electron micrographs (PDB entry 2om3). The virus is composed of one strand of RNA (shown in red) wrapped inside a sheath of protein (shown in blue). The protein coat is composed of about 2130 copies of a small protein, which stack like bricks in a cylindrical chimney. The RNA strand encodes four proteins, which together orchestrate the life cycle of the virus. These include two proteins that replicate the viral RNA, a protein that transports the RNA from cell to cell, spreading the infection, and the capsid protein seen in the PDB structures.

Read the rest from David Goodsell at the RCSB PDB, here.

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