Viruses hexon

An icosahedral virus particle composed of 252 capsomeres 240 being hexons and 12 being pentons... 

Because eicosahedra are regular geometric solids and the faces can be made up of hexons and pentons of identical subunits, it might seem that self-assembly of eicosahedral viruses would occur easily. However, the subunits usually must be able to assume three or more different conformations and the shells can easily be assembled incorrectly. Several stategies are em-... 

The structure of the capsid (protein shell) for an icosahedral virus such as tomato bushy stunt virus. Pentons (P) are located at the 12 vertices of the icosahedron. Hexons (H), of which there are 20, form the edges and faces of the icosahedron. Each penton is composed of five protein subunits and each hexon is composed of six protein subunits. In all, the structure contains 180 protein subunits. 

Larger icosahedral viruses that have been structurally well characterized do not obey the simple quasi-equivalence rule. For example, adenovirus capsids, for which T = 25, are built of 240 hexons (six-coordinated units) that are trimers of the major structural protein, and the 12 pentons consist of a different protein (Burnett 1984). Polyomavirus capsids, for which T = 7, are built of a single major structural protein,... 

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. 

Fig. 4. Adenovirus and bacteriophage PRDl. Top On the left, a density isosurface representation of adenovirus at 25-A resolution is shown. The 5-fold axis, occupied by the protein penton, is marked with a pentagon. A trimer of hexon is marked with a triangle close by arrays of hexon extend outward in all directions from the pentagonal vertex, forming the flat faces of the virus. On the right, a close-up of the 5-fold axis is shown (top) and below that a close-up of the hexon trimer with it crystal structure fitted (Athappilly et at, 1994 Stewart et al, 1991). Bottom The Susl mutant of PRDl is shown...

Perhaps the most spectacular homology seen to date is the similarity between the hexon protein of a mammalian virus, adenovirus, and the P3 coat protein of a bacteriophage PRDl, both containing two jelly-roll domains (Athappilly et al, 1994 Benson et al, 1999). This only goes to show that as our understanding of other viral proteins expands, so will the homologies that will likely become apparent. 

To better augment the structural differences between the hexons and pentons that are being discerned by VP5, the virus was decorated with the antibody 6F10 [110]. The residues being recognized by this antibody were... 

Wingfield, P. T., Stahl, S.J., Thomsen, D. R., Homa, F. L., Booy, F. P., Trus, B. L., and Steven, A. C. (1997). Hexon-only binding of VP26 reflects differences between the hexon and penton conformations fo VP5, the major capsid protein of herpes simplex virus./ Virol. 71, 8955-8961. 

K. L., Baker, T. S., and Smith, T. J. (2002). An antibody to the putative aphid recognition site on cucumber mosaic virus recognizes pentons but not hexons. /. Virol. 76, 12250-12258. 

Chen, D.H., et al. The pattern of tegument-capsid interaction in the herpes simplex virus type 1 virion is not influenced by the small hexon-associated protein VP26. Journal of Virology, 2001, 75 (23), p. 11863-11867. 

However, this assay has a limit of quantitation of 10 particles mL , and for more dilute samples we sought other quantitative methods - for example, using amplification with PCR, to assess virus particle count. A quantitative real-time (TaqMan) PCR procedure was developed utilizing amplification of a portion of the Ad5 hexon gene. When samples were treated with 0.05% sodium dodecyl sulfate (SDS) and standard PCR reaction conditions applied, this assay was shown to... 

Adenoviruses consist of a large double-stranded DNA genome (about 36 kilobase pairs long) packaged within a nonenveloped icosahedral capsid that is primarily composed of three virus-encoded proteins (hexon, pen ton base, and fiber proteins) [39]. The fiber proteins protrude fi om the surface of the virus and mediate its attachment to target cells via a high affinity interaction with the cellular receptor CAR (coxsackievirus and adenovirus receptor) [40]. The virus is then internahzed into endosomal vesicles via specific interactions between the penton base proteins and ofy integrins [41]. Adenoviruses escape these vesicles by an acid-induced endosomolytic activity and are transported to the nucleus, into which they enter via pores in the nuclear membrane [42]. 

Fig. 1. Time course of synthesis of viral DNA, RNA, and proteins and virion assembly in Ad2-infected cells. The measurements of intracellular virus and viral DNA (pfu/cell) are from Green et al. (1971), and those of viral mRNA, measured by hybridization of [ H]-RNA to Ad2 DNA, and late protein, and hexon antigen measured by complement fixation from Philipson and Lindberg (1974). Modified from Tooze (1980).

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