Virus, filamentous

Home RW, Pasquali-Ronchetti I. A negative staining carbon film technique for studying vimses in the electron microscope. I. Preparative procedure for examining icosahedral and filamentous viruses. J Ultrastructure Res 1974 47 361-383. 

Fibrillar forms of biological macromolecules—such as collagen, DNA, muscle proteins, and filamentous viruses—have been elucidated using fiber and powder diffraction methods (Fraser and MacRae, 1973). 

Many important biological substances do not form crystals. Among these are most membrane proteins and fibrous materials like collagen, DNA, filamentous viruses, and muscle fibers. Some membrane proteins can be crystallized in matrices of lipid and studied by X-ray diffraction (Chapter 3, Section III.D), or they can be incorporated into lipid films (which are in essence two-dimensional crystals) and studied by electron diffraction. I will discuss electron diffraction later in this chapter. Here I will examine diffraction by fibers. 

Bee chronic paralysis virus Bee filamentous virus Crystalline array virus... 

Both X-ray and neutron fiber diffraction (as well as electron microscopy) techniques have been applied to filamentous viruses, for which the prospect of three-dimensional crystals is poor. By combining neutron and X-ray fiber diffraction, NMR, circular dichroism, and Raman and infrared spectroscopies, an atomic model for the filamentous bacteriophage Pfl has been derived (Liu and Day, 1994). Other studies concerning Pfl have relied on purely X-ray fiber diffraction data, together with molecular modeling, to provide detailed filament structures (Pederson et at, 2001 Welsh et at, 1998a,b, 2000). Eiber diffraction was also used to solve the structure of the rodlike helical tobacco mosaic virus (TMV), where all of the coat protein and three genomic nucleotides... 

Filamentous viruses have been studied mostly by fiber diffraction (Namba et al., 1989). Fibers can be considered to be crystals in which there is rotational disorder about the helical axis. This has the effect of smearing the discrete spots of crystalline diffraction into layer lines. There is a resulting loss of information, but sufficient experimental observations can be made for highly symmetric virus structures so that a unique high-resolution structure is obtainable (Makowski, 1991). 

The maximum entropy principle has been applied already, for example, in the structure determination of the Pfl filamentous virus at 4 A resolution [264]. Combination of the data from one heavy atom derivative and the maximum entropy method led to an interpretable map which showed the helical subunits of the virion. 

Helical symmetry The polymeric proteins of filamentous viruses and the cytoskel-ton possess helical symmetry, in which subunits are related by a translation, as well as a rotational component. Actin, myosin, tubulin and various other fibrous proteins all interact with helical symmetry, which is often called screw symmetry. Screw symmetry, which relates the positions of adjacent subunits, combines a translation along the helix axis with the rotation. Actin forms a two-stranded helix of globular actin subunits. However, important variations in the helix parameters occur (Egehnan et al, 1982). The rise per subunit is relatively constant, but the twist or relative rotation around the helix axis is highly variable. This polymorphic tendency is probably important for the smooth functioning of muscle contraction, which involves considerable force generation. 

STEM studies have characterized many varieties of filamentous viruses according to length, MIL, and radial density profile. Models have been proposed by combining the data from biochemical, biophysical, and STEM studies (Marzec and Day, 1994) and a controversial model for Pf 1 has been proposed (Liu and Day, 1994). Many studies of spherical viruses have been carried out (Newcomb et ai, 1993 Paredes et ai, 1992). 

A long nonoccluded filamentous virus, morphologically distinct from the polydnaviruses, was characterized from the reproductive tract of the parasitoid C, marginiventris. Though the role of the filamentous virus in the parasitoid-host interaction is unknown, the virus was reported to replicate in hypodermal and tracheal matrix cells of the host larvae (113). 

Filamentous viruses, which are high-aspect ratio agents that proliferate in the presence of host cells, have regular self-assembled structures, and the viral coat proteins on their surface can be genetically or chemically modified to functionalise the nanovector. The tobacco mosaic virus is one of the most extensively studied ID structure for nanoscale applications, and their properties, functionalisation, and assembly into nanodevices are highlighted in the recent review by Ghodssi and co-workers. Mao and co-workers have recently demonstrated that filamentous bacteriophage can be converted into novel photo-responsive nanowires... 

Fiiovirus A filamentous virus that displays unusual variability in shape. Two filo-viruses, the Ebola virus and the Marburg virus, have been associated with human disease. 

Other applications of polarized IR spectroscopy in molecular biophysics have included studies of the orientations of tryptophan side chains in a filamentous virus [78] and studies of folding of integral membrane proteins [48, 79]. 

Tsuboi, M., Overman, S.A., Thomas Jr., G.J. Orientation of tryptophan-26 in coat protein subunits of the filamentous virus Ff by polarized Raman microspectroscopy (1996). Biochemistry 35, 10403-10410 (1996)... 

Tsuboi, M. et al. (2000) Intensity of the polarized Raman band at 1340-1345 cm-1 as an indicator of protein alpha-helix orientation application to Pfl filamentous virus. Biochemistry, 39 (10), 2677 - 2684. 

Dogic, Z. Purdy, K. R. et al. (2004). "Isotropic-nematic phase transition in suspensions of filamentous virus and the neutral polymer Dextran." Phys Rev E Stat Nonlin Soft Matter Phys,69(5 Pt 1), 051702. 

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