Article Information

• PDF (2205 kb)

PubMed

• Articles by P.J. Butler
• Articles by G.P. Lomonossoff

Related Articles

• Physical Regulation of the Self-Assembly of Tobacco Mosaic V...

  Physical Regulation of the Self-Assembly of Tobacco Mosaic Virus Coat Protein Biophysical Journal, Volume 91, Issue 4, 15 August 2006, Pages 1501-1512 Willem K. Kegel and Paul van der Schoot Abstract We present a statistical mechanical model based on the principle of mass action that explains the main features of the in vitro aggregation behavior of the coat protein of tobacco mosaic virus (TMV). By comparing our model to experimentally obtained stability diagrams, titration experiments, and calorimetric data, we pin down three competing factors that regulate the transitions between the different kinds of aggregated state of the coat protein. These are hydrophobic interactions, electrostatic interactions, and the formation of so-called “Caspar” carboxylate pairs. We suggest that these factors could be universal and relevant to a large class of virus coat proteins. Abstract | Full Text | PDF (192 kb)

• Structure of the Stacked Disk Aggregate of Tobacco Mosaic Vi...

  Structure of the Stacked Disk Aggregate of Tobacco Mosaic Virus Protein Biophysical Journal, Volume 74, Issue 1, 1 January 1998, Pages 595-603 Rubén Díaz-Avalos and Donald L.D. Caspar Abstract The coat protein of tobacco mosaic virus is known to form three different classes of aggregate, depending on environmental conditions, namely helical, disk, and A-protein. Among the disk aggregates, there are four-layer, six-layer, and long stacks, which can be obtained by varying the ionic strength and temperature conditions during the association process. The four-layer aggregate has been crystallized, and its structure solved to atomic resolution. The stacked disk aggregate had been presumed to be built of a polar two-layer disk related to the crystalline A and B rings. A study using monoclonal antibodies specific to the bottom surface of TMV protein demonstrated that the stacked disk aggregate is bipolar, and suggested that the repeating two-layer unit might be similar to the dihedrally symmetrical A-ring pair in the disk crystal. In this paper we present a three-dimensional reconstruction of the stacked disk aggregate obtained by electron microscopy of ice-embedded samples. After modeling of the structure, we found the ring pairs to have the same quaternary structure as the A-ring pair of the four-layer aggregate. The resolution achieved in the image processing of the electron micrographs is on the order of 9Å in the meridional direction and 12Å in the equatorial. The identification of the structure of the stacked disk with the A-ring pair of the disk crystal provides an explanation of the observation that the axial periodicity of the disk pair, which is ∼53Å when fully hydrated, can shrink to ∼43Å in the dry state. Abstract | Full Text | PDF (528 kb)

• Refined Atomic Model of the Four-Layer Aggregate of the Toba...

  Refined Atomic Model of the Four-Layer Aggregate of the Tobacco Mosaic Virus Coat Protein at 2.4-Å Resolution Biophysical Journal, Volume 74, Issue 1, 1 January 1998, Pages 604-615 Balaji Bhyravbhatla, Stanley J. Watowich and Donald L.D. Caspar Abstract Previous x-ray studies (2.8-Å resolution) on crystals of tobacco mosaic virus coat protein grown from solutions containing high salt have characterized the structure of the protein aggregate as a dimer of a bilayered cylindrical disk formed by 34 chemically identical subunits. We have determined the crystal structure of the disk aggregate at 2.4-Å resolution using x-ray diffraction from crystals maintained at cryogenic temperatures. Two regions of interest have been extensively refined. First, residues of the low-radius loop region, which were not modeled previously, have been traced completely in our electron density maps. Similar to the structure observed in the virus, the right radial helix in each protomer ends around residue 87, after which the protein chain forms an extended chain that extends to the left radial helix. The left radial helix appears as a long -helix with high temperature factors for the main-chain atoms in the inner portion. The side-chain atoms in this region (residues 90–110) are not visible in the electron density maps and are assumed to be disordered. Second, interactions between subunits in the symmetry-related central A pair have been determined. No direct protein-protein interactions are observed in the major overlap region between these subunits; all interactions are mediated by two layers of ordered solvent molecules. The current structure emphasizes the importance of water in biological macromolecular assemblies. Abstract | Full Text | PDF (1445 kb)

• …more

Abstract

Assembly of tobacco mosaic virus is initiated by the binding of a specific loop of the RNA into the central hole of the disk aggregate of protein subunits. Since the nucleation loop is located about five-sixths along the RNA molecule, subsequent elongation must be bidirectional. We have now measured the rates of elongation in the two directions by determining the lengths of RNA protected from nuclease digestion at different times and using either intact TMV rNA, or RNA with most of the longer tail removed. Comparison of the rates with the protein supplied as either a mixture of disks with A-protein (a mixture of less aggregated states) or just A-protein, shows that different mechanisms and protein aggregates are used for the most rapid growth. When disks are present, they add more rapidly along the longer RNA tail but do not appear to add directly on the shorter tail. In contrast, smaller aggregates (A-protein) can add at both ends of the rod, but do so more slowly. Mechanisms for these processes are discussed. Preliminary results on the binding of the specific hexanucleotide AAGAAG to the disk are given and compared with the known changes on binding nonspecific hexanucleotides or the trinucleotide AAG.