Sandbox TMV
Tobacco Mosaic Virus
ContentsTobacco Mosaic VirusTobacco Mosaic Virus (TMV) is a positive-sense single stranded RNA virus that infects plants, especially tobacco and other members of the family Solanaceae. The infection causes characteristic patterns, such as "mosaic"-like mottling and discoloration on the leaves (hence the name). TMV was the first virus to ever be discovered. It is composed of 2130 identical coat protein subunits following the right-handed helix of an accompanying RNA strand to produce a 300 nm hollow cylinder with an outer diameter of 18 nm and a 4 nm wide central channel. This here is a protein-nucleic acid interactions in the virus. CarboxylatesTwo clusters of acidic amino acids are thought to be important for the disassembly of the helical structure of TMV. When the virus enters cells, the higher pH and lower calcium levels increase the repulsion of neighboring carboxylates, destabilizing the capsid. This concept was originally proposed by Caspar and subsequently examined by site-directed mutagenesis [1]. Several carboxylates were identified including Glu50 and ASP77, which contact each other in the helical stack by hydrogen bond (look closely at the two subunits that overlap in this lockwasher complex), and a cluster of four acidic amino acids, GLU95, GLU97, GLU106 and GLU109, near the center of the ring. There are phosphate carboxylates in the structure of the virus, the phosphate-carboxylates are presented in the color teal in the molecule. They are calcium-binding sites along with the carboxylates. When phosphate-carboxylates bind to calcium it makes the capsid more stable. When the phosphate- carboxylates or the carboxylates are not present then capsid will be unstable, since there will not be anything to bind to calcium. Here is a display of pbd 2TMV showing the virus with calcium in pink binding to carboxylates in order to stabilize the capsid. This section complements the article on Tobacco Mosaic Virus in the Molecule of the Month Series. See also Teaching Scenes, Tutorials, and Educators' Pages. Repeating SubunitsTh repeating basic unit consists of 49 subunits which cover a section of 69 Å of height in three turns of the helix (= a rise of 23 Å per turn). A single strand of RNA is placed between the protein subunits at a distance of 40 Å from the outer diameter. The figure depicts one basic unit. Protein and RNA are shown in spacefill mode, RNA in white, the protein changing from red to blue along the helix. The uppermost subunit is marked light brown. Each protein subunit covers three nucleotides of the RNA. 
TransmissionIt is transmitted mechanically by the virus coming in contact with injured cells of a host plant. The primary mechanism for this is contaminated worker's hands or equipment that comes into contact with a healthy plant. Contaminated hands can be freed of the virus by washing with a detergent. The virus can be inactivated on equipment by scrubbing it with a brush using detergent or by steaming. Although the virus is transmitted primarily on worker's hands and equipment, anything that mechanically moves the virus from a source to a healthy plant can transmit it. Chewing insects, such as flea beetles and grasshoppers, are capable of transmitting the virus, but such transmission is very rare in nature. Seed may be infested with the virus and transmit the virus. Sign and SymptomsSymptoms that occur by Tobacco mosaic virus dependent on the plant's host. The symptoms include mosaic, mottling, necrosis, stunting, leaf curling, and yellowing of the tissues of the plant. All the symptoms depend on the age of the plant, the environment's condition, the virus strain, and the genetic background of the host plant. Strains of TMV also infect tomato, sometimes causing poor yield or distorted fruits, delayed fruit ripening, and nonuniform fruit color. TreatmentTMV can easily overwinter on the seed coat, thus providing an inoculum source for the next planting cycle. Therefore, it is important to treat TMV-contaminated tobacco seed with a 10% solution of trisodium phosphate for 15 minutes. Alternatively, tomato seed contaminated with TMV can be incubated at 70°C/158°F for 2-4 days prior to planting. Both treatments will inactivate the virus that is on the seed coat, but should have little negative effect on seed germination.
Publication Abstract from PubMed
The structure of tobacco mosaic virus (TMV) has been determined by fiber diffraction methods at 2.9 A resolution, and refined by restrained least-squares to an R-factor of 0.096. Protein-nucleic acid interactions are clearly visible. The final model contains all of the non-hydrogen atoms of the RNA and the protein, 71 water molecules, and two calcium-binding sites. Viral disassembly is driven by electrostatic repulsions between the charges in two carboxyl-carboxylate pairs and a phosphate-carboxylate pair. The phosphate-carboxylate pair and at least one of the carboxyl-carboxylate pairs appear to be calcium-binding sites. Nucleotide specificity, enabling TMV to recognize its own RNA by a repeating pattern of guanine residues, is provided by two guanine-specific hydrogen bonds in one of the three base-binding sites. Visualization of protein-nucleic acid interactions in a virus. Refined structure of intact tobacco mosaic virus at 2.9 A resolution by X-ray fiber diffraction., Namba K, Pattanayek R, Stubbs G, J Mol Biol. 1989 Jul 20;208(2):307-25. PMID:2769760 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. About this Structure2TMV is a 2 chains structure with sequences from Tobacco mosaic virus. The January 2009 RCSB PDB Molecule of the Month feature on Tobacco Mosaic Virus by David Goodsell is 10.2210/rcsb_pdb/mom_2009_1. Full crystallographic information is available from OCA.
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3D structures of tobacco mosaic virus
Updated on 21-November-2013
Teaching Scenes, Tutorials, and Educators' Pages, 2xea – TMV coat protein + RNA - CryoEM
2tmv – TMV coat protein + RNA - fiber
References
Primary Reference
Visualization of protein-nucleic acid interactions in a virus. Refined structure of intact tobacco mosaic virus at 2.9 A resolution by X-ray fiber diffraction., Namba K, Pattanayek R, Stubbs G, J Mol Biol. 1989 Jul 20;208(2):307-25. PMID:2769760
Additional References
Created with the participation of Jaime Prilusky, Eran Hodis, David S. Goodsell.
