Virus, structure

Can any number of identical subunits be accommodated in the asymmetric unit while preserving specificity of interactions within an icosahedral arrangement This question was answered by Don Caspar then at Children s Hospital, Boston, and Aaron Klug in Cambridge, England, who showed in a classical paper in 1962 that only certain multiples (1, 3, 4, 7...) of 60 subunits are likely to occur. They called these multiples triangulation numbers, T. Icosahedral virus structures are frequently referred to in terms of their trian-gulation numbers a T = 3 virus structure therefore implies that the number of subunits in the icosahedral shell is 3 x 60 = 180. 

Figure 16.6 A T = 3 icosahedral virus structure contains 180 subunits in its protein shell. Each asymmetric unit (one such unit is shown in thick lines) contains three protein subunits A, B, and C. The icosahedral structure is viewed along a threefold axis, the same view as in Figure 16.5. One asymmetric unit is shown in dark colors.

Satellite tobacco necrosis virus is an example of a T = 1 virus structure. The 60 identical subunits interact tightly around the fivefold axes on the surface of the shell and around the threefold axes on the inside. These interactions form a scaffold that links all subunits together to complete the shell. 

Rossmann, M.G. Virus structure, function, and evolution. Harvey Lectures, Series 83 107-120, 1989. 

Three types of particles are associated with FIBV small spherical particles, 22 nm in diameter tubular particles, also having a diameter of 22 nm and larger spherical particles (42 nm diameter) known as the Dane particles. The Dane particle alone has a typical virus structure and appears to be infectious but is the least common form. It consists of... 

When a virus multiplies, the genome becomes released from the coat. This process occurs during the infection process. The present chapter is divided into three parts. The first part deals with basic concepts of virus structure and function. The second part deals with the nature and manner of multiplication of the bacterial viruses (bacteriophages). In this part we introduce the basic molecular biology of virus multiplication. The third part deals with important groups of animal viruses, with emphasis on molecular aspects of animal virus multiplication. 

The complete complex of nucleic acid and protein, packaged in the virus particle, is called the virus nucleocapsid. Although the virus structure just described is frequently the total structure of a virus particle, a number of animal viruses (and a few bacterial viruses) have more complex structures. These viruses are enveloped viruses, in which the nucleocapsid is enclosed in a membrane. Virus membranes are generally lipid bilayer membranes, but associated with these membranes are often virus-specific proteins. Inside the virion are often one or more virus-specific enzymes. Such enzymes usually play roles during the infection and replication process. 

Fig. 1. Nucleotide sequence of the SFV 26 S RNA (top row), the corresponding amino acid sequence (middle row), and the amino acid sequence of the Sindbis virus structural proteins (bottom row). Nucleotides are numbered from the 5 end of the RNA molecule and all amino adds from the amino terminus of each protein. The amino- and the carboxyl-terminal ends of each protein are indicated hy arrows, glycosylation sites by triangles, and membrane-spanning regions of the viral glycoproteins by underlines for Sindbis virus and overlines for SFV. Amino acids in boxes are negatively charged (Asp and Glu), and those circled are positively charged (Lys and Arg). Some restriction endonuclease cleavage sites are shown on the nucleotide sequence. The alignment of the amino acid...

Twenty five years on from the first spherical virus structures, the complexity of the isometric virus... 

The Laue method (using white radiation) has not yet been used for a de novo virus structure determination. Whilst this method continues to have potential for stud)dng d)mamic events it compounds the problem of spot resolution and will only be feasible with detectors with greater resolution than is furnished by current CCD detectors. 

The refined coordinates will correspond to either the icosahedral asymmetric unit or the crystallographic asymmetric unit, hence symmetry operations must be applied to generate the whole capsid. A useful repository of virus structure information is the website http // viperdb.scripps.edu/ where portions of the viral capsid can be generated. 

Viruses borrow heavily on the host enzymatic machinery to obtain energy for synthesis, as well as for replication, transcription, and translation. The virus infective cycle is strongly irreversible. Virus infection is followed by the gradual turning on of viral genes. Viral enzymes are the first viral gene products in late infection, the virus structural proteins are favored. The irreversible lytic cycle of the virus is directed by a cascade of controls. 

Das, D., and Georgiadis, M. M. (2004). The crystal structure of the monomeric reverse transcriptase from Moloney murine leukemia virus. Structure 12, 819-829. 

An initial approach to fullerene enumeration was based on point-group symmetry (Fowler 1986 Fowler et al. 1988) and involved an extension of Coxeter s (1971) work on icosahedral tessellations of the sphere and of methods for the classification of virus structures (Caspar Klug 1962). This approach led to magic numbers in fullerene electronic structure (Fowler Steer 1987 Fowler 1990) and will be described briefly here. 

Burnett, R. M. 1984 Structural investigations of hexon, the major coat protein of adenovirus. In Biological macromolecules and assemblies (Volume 1 Virus structures) (ed. F. A. Jurnak A. McPherson), pp. 377-385. New York John Wiley Sons. 

Caspar, D. L. D. 1992 Virus structure puzzle solved. Current Biol. 2, 169-171. 

Bamford, D. H. Virus structures Those magnificent molecular machines. Curr. Bio. 10, R558-R561... 

Jumak FA, McPherson A (eds) (1984) Biological macromolecule and assemblies. Volume 1 Virus Structure , Wiley. 

Janik, J. E., Huston, M. M., Cho, K. and Rose, J. A. (1989). Efficient synthesis of adeno-associated virus structural proteins requires both adenovirus DNA binding protein and VA I RNA. Virology 168, 320-329. 

Baumert TF, Ito S, Wong DT, Liang TJ (1998), Hepatitis C virus structural proteins assemble into virus-like particles in insect cells, J. Virol. 72 3827-3836. 

LLu YC, Bentley WE (1999), Enhancing yield of infectious Bursal disease virus structural proteins in baculovirus expression systems focus on media, protease inhibitors, and dissolved oxygen, Biotechnol Prog. 15 1065-1071. 

Indeed, the discoverers of virus structures, Donald Caspar and Aaron Klug stated that... 

Mackay called attention to yet another limitation of the 230 space-group system. It covers only those helices that are compatible with the three-dimensional lattices. All other helices that are finite in one or two dimensions are excluded. Some important virus structures with icosahedral symmetry are among them. Also, there are very small... 

R.E. Webster, J. Lopez, Structure and assembly of the class 1 filamentous bacteriophage. In Virus Structure and Assembly (S. Casjens Ed.), pp 235-268, Jones Bartlett, Boston, 1985. 

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