Virion diameter

Influenza virus particles are spheroidal and approximately 100 nm in diameter. The outer-membrane envelope contains 500 copies of hemagglutinin (HA) trimers and 100 copies of neuraminidase tetramers. The hemagglutinin constitutes the receptor sites for a-sialoside ligands. X-ray analyses show that the three sialic acid binding pockets reside 46 A apart, each trimer being separated on the virion surface by about 65-110 A [42],... 

Only Type A influenza vims has been found to be capable of producing pandemics. The influenza A virus is identified as a medium-size RNA virus, some lit) nanometers in diameter and delimited by a membrane of lipids and polysaccharides derived from the host cell and virus-specific protein. Five distinct proteins have been identified, three of which are inside the virion. A schematic representation of the influenza virus emerging from a cell is given in Fig. 2. 

CPMV particles have an icosahedral symmetry with a diameter of approximately 28 nm (Figure 9.2), the protein shell of the capsid is about 3.9nm thick [72], The structure of CPMV is known to near-atomic resolution (Figure 9.3) [73], The virions are formed by 60 copies of two different types of coat proteins, the small (S) subunit and the large (L) subunit. The S subunit (213 amino acids) folds into one jelly roll P-sandwich, and the L subunit (374 amino acids) folds into two jelly roll P-sandwich domains. The three domains form the asymmetric unit and are arranged in a similar surface lattice to T = 3 viruses, except they have different polypeptide sequences therefore the particle structure is described as a pseudo T = 3 or P = 3 symmetry [74]. 

As a close relative to the brome mosaic virus the cowpea chlorotic mottle vims (CCMV) possesses an outer diameter of 28 nm, is assembled from 180 subunits that create an icosahedral type structure, and contains an RNA core. " Another similarity is the cationic interior surface of the viral capsid which is formed from subunits with highly basic N-termini (6 positively charged arginine and 3 lysine residues) that project into the cavity and stabilize the RNA core. However as a potential biomineralization template, the electrostatic environment of the virion cavity precludes any cationic metal precursors and thus limits its applicability for nanoparticle synthesis. 

Reoviridae—Nearly spherical, diameter 600-800 A, nonenveloped, two or three concentric icosahedral protein shells. Outer shell structure depends on genus. Virions contain the transcriptional machinery... 

Reoviruses are nonenveloped virions with icosahedral symmetry and consist of two concentric protein shells, termed the outer capsid and core [15]. These virions encapsidate a genome of 10 double-stranded RNA gene segments. Reovirus strain type 1 Lang (TIL) has a diameter of 850 A and 600 projections composed of the uS protein [147]. uS interdigitates with a more internal layer composed of 600 copies of fil protein to form the outer capsid. At each icosahedral 5-fold axis, pentamers of 2.2 protein... 

The HSV-1 virion is approximately 20 run in diameter and consists of four components envelope, tegument, capsid, and viral genome. The envelope is derived from the cellular membrane and contains approximately 12 viral glycoproteins essential for viral entry. The tegument is the protein layer between the capsid and the envelope and contains at least 10 viral proteins, including VP 16 (essential for transactivation and virion envelopment), VP22 (membrane translocation domain), and virion host shut off (vhs) protein. The capsid consists of 7 viral proteins and contains the linear dsDNA genome, which is 152 kb in size. 

Fig. 3.44 Intermittent contact AFM of two virions in linear arrangement on graphite (reproduced with permission from [96]). The measured height of 18 nm corresponds to the true diameter, while the width (ca. 85 nm (fwhm)) is attributed to the AFM tip shape. Reproduced with permission from [96]. Copyright 2004. American Chemical Society...

Viruses occur in a bewildering array of sizes and shapes. Virions (complete viral particles) range from 10 nm to approximately 400 nm in diameter. Although most viruses are too small to be seen with the light microscope, a few (e.g., the pox viruses) can be visualized because they are as large as the smallest bacteria. 

One of the most pressing problems of the age is, of course, AIDS which is caused by HIV. The HIV virion is about 1000 A in diameter. It has not been possible so far to crystallise this virus. Instead, the individual proteins are being crystallised for detailed study. There is no doubt, however, that the architecture of the plant and mammalian viruses referred to earlier, determined by X-ray crystallography, are very important to the general understanding of HIV and thereby the AIDS disease. 

For evaluation of 6 we have assumed that the virus would be hexagonally closest-packed in a two-dimensional array on the adsorbent surface where 6 equals unity. The quantity x was estimated to be 50 from space filling models where approximately 3% of a 27-nm diameter icosahedral virion face is estimated, on the basis of globular protein structure (12), to approach the surface of the solid close enough to displace interfacial water molecules. If our estimate is changed to 10 or 250, instead of a most probable value of about 50, Equation 2 predicts that the AGads will be shifted by only zb 4 kj mol, which is comparable to the uncertainty given by experimental data scatter. 

The virus particles are spherical and have an average diameter of 110-130 nanometers. All are enveloped in a lipid (fat) membrane. Viewed in cross-section, they show grainy particles that are ribosomes acquired from their host cells. It is this characteristic that gave them their name, derived from the Latin "arena," which means "sandy." Their genome, or genetic material, is composed of RNA only, and while their replication strategy is not completely understood, we know that new viral particles, called virions, are created by budding from the surface of their ho.sfs cells. 

Structurally, filovirus virions (complete viral particles) may appear in several shapes, a biological feature called pleomorphism. These shapes include long, sometimes branched filaments, as well as shorter filaments shaped like a "6", a "U", or a circle. Viral filaments may mea.sure up to 14,000 nanometers in length, have a uniform diameter of 80 nanometers, and are enveloped in a lipid (fatty) membrane. Each virion contains one molecule of. single-stranded, negative-sen.se RNA. New viral particles are created by budding from the surface of their hosts cells however, filovirus replication strategies are not completely understood. 

The NV is a human calicivims and contains a single-stranded RNA genome.Particles of NV have T=3 icosahedral symmetry with an approximate outer diameter of 38 nm and an average inner diameter of the central cavity that ranges from 20-29 nm. These virions contain 180 molecules of identical capsid protein (56.6 kl/)a each), which has two principle domains, S and P. linked by a flexible hinge.These viruses arc difficult to cultivate in tissue culture systems or animals,"" making them difficult to study, and this factor limits their use as nanosynthctic reaction vessels. 

The picornavirus particle is composed of a molecule of single-stranded RNA (50 by weight) enclosed in a capsid of protein (70%) There is no good evidence for the presence of carbohydrate or lipid in the virion (1). As viewed in the electron microscope by negative staining, the particle is isometric with a dry diameter of 27-28 nm. In solution it behaves as a spheroid (frictional ratio of 1.05-1 10) with a diameter of about JO nm, and containing some 0.25 g water per gram of dry virus (2). 

In 1959 Finch and Klug examined crystals of poliovirus by X-ray diffraction and concluded that the virion possessed icosahedral symmetry. Extrapolating from the experimental data, they also suggested that the capsid was made up on 60 identical asymmetric structure units with a diameter of 6O-65 Based upon the then accepted values of 6.7 x 10 for the particle weight of the virion and 2x10 for the molecular weight of the RUA, they calculated a molecular weight for the structure unit of 80,000 (28). 

It may therefore be concluded that the asymmetric structure unit of the picornaviral capsid is composed of three polypeptides and conforms to the prediction of Finch and Klug. It has a molec]jlar mass of approximately 86,000 daltons, a diameter of about 68 A (35) and is repeated 60 times in the virus capsid. This corresponds to the simplest icosahedral lattice, with a triangulation number of 1 (57) Considering the I4S pentamers as capsomeres, there would be 12 capsomeres per virion. The location of the 6 (7P4) polypeptides in the capsid has not yet been established, but it is possible that they are distributed over the internal surface and in direct contact with the virion RNA (5Q, 39I see below). 

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