Capsid - Wikipedia
Treatment of the DNA-protein complex with alkaline pH resulted in the specific removal of FP1. Links to PubMed are also available for Selected References. . disulfide bonds: an important structural feature of the polyoma virus capsid. The capsomere is a subunit of the capsid, an outer covering of protein that protects the genetic material of a virus. Capsomeres self-assemble to form the capsid. 3) Complex- e.g., that exhibited by poxvirus and rhabdovirus. This group comprises Edit links. This page was last edited on 5 November , at (UTC). The capsomeres in the capsid shell are joined together via complexes known as These phylogenetic relationships are of great interest to researchers.
Characterization of components released by alkali disruption of simian virus Plaque assay for polyoma virus on primary mouse kidney cell cultures. Electron microscopy of defined lengths of chromatin. In vitro reassembly of shell-like particles from disrupted polyoma virus. Structural roles of polyoma virus proteins. Rapid concentration and purification of polyoma virus and SV40 with polyethylene glycol. Electrophoretic analysis of the structural polypeptides of polyoma virus mutants.
Decapsidation of polyoma virus: Properties of nucleoprotein complexes containing replicating polyoma DNA. Separation by equilibrium centrifugation in CsC1 gradients of density--labelled and normal deoxyribonucleoprotein from chromatin. Early events in polyoma virus infection: Origin of the polyoma virus-associated endonuclease. Characterization of polyoma DNA-protein complexes.
Virus: Structure and Symmetry
Electrophoretic identification of the proteins in a nucleoprotein complex isolated from polyoma-infected cells. In vitro radioisotopic labeling of proteins associated with purified polyoma virions. Immunological reactivity of antisera to sodium dodecyl sulfate-derived polypeptides of polyoma virions. On the nucleoprotein core of simian virus Capsids are formed as single or double protein shells and consist of only one or a few structural protein species.
Therefore, multiple protein copies must self assemble to form the continuous three-dimensional capsid structure.
Self assembly of virus capsids follows two basic patterns: Some virus families have an additional covering, called the envelope, which is usually derived in part from modified host cell membranes. Viral envelopes consist of a lipid bilayer that closely surrounds a shell of virus-encoded membrane-associated proteins.
The exterior of the bilayer is studded with virus-coded, glycosylated trans- membrane proteins. Therefore, enveloped viruses often exhibit a fringe of glycoprotein spikes or knobs, also called peplomers. In viruses that acquire their envelope by budding through the plasma or another intracellular cell membrane, the lipid composition of the viral envelope closely reflects that of the particular host membrane.
The outer capsid and the envelope proteins of viruses are glycosylated and important in determining the host range and antigenic composition of the virion. In addition to virus-specified envelope proteins, budding viruses carry also certain host cell proteins as integral constituents of the viral envelope.
Virus envelopes can be considered an additional protective coat. Larger viruses often have a complex architecture consisting of both helical and isometric symmetries confined to different structural components.
Classification of Viruses Viruses are classified on the basis of morphology, chemical composition, and mode of replication.
The viruses that infect humans are currently grouped into 21 families, reflecting only a small part of the spectrum of the multitude of different viruses whose host ranges extend from vertebrates to protozoa and from plants and fungi to bacteria.
Morphology Helical Symmetry In the replication of viruses with helical symmetry, identical protein subunits protomers self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path.
Such nucleocapsids form rigid, highly elongated rods or flexible filaments; in either case, details of the capsid structure are often discernible by electron microscopy. In addition to classification as flexible or rigid and as naked or enveloped, helical nucleocapsids are characterized by length, width, pitch of the helix, and number of protomers per helical turn.
- There was a problem providing the content you requested
- Meaning of "capsomere" in the English dictionary
- Difference Between Capsid and Envelope
The most extensively studied helical virus is tobacco mosaic virus Fig. Many important structural features of this plant virus have been detected by x-ray diffraction studies.
Difference Between Capsid and Envelope | Definition, Characteristics, Function
Figure shows Sendai virus, an enveloped virus with helical nucleocapsid symmetry, a member of the paramyxovirus family see Ch. Figure The helical structure of the rigid tobacco mosaic virus rod. About 5 percent of the length of the virion is depicted. Individual 17,Da protein subunits protomers assemble in a helix with an axial repeat of 6.
Figure Fragments of flexible helical nucleocapsids NC of Sendai virus, a paramyxovirus, are seen either within the protective envelope E or free, after rupture of the envelope. The intact nucleocapsid is about 1, nm long and 17 nm in diameter; its pitch more Icosahedral Symmetry An icosahedron is a polyhedron having 20 equilateral triangular faces and 12 vertices Fig.
Lines through opposite vertices define axes of fivefold rotational symmetry: Lines through the centers of opposite triangular faces form axes of threefold rotational symmetry; twofold rotational symmetry axes are formed by lines through midpoints of opposite edges. An icosaheron polyhedral or spherical with fivefold, threefold, and twofold axes of rotational symmetry Fig. Figure Icosahedral models seen, left to right, on fivefold, threefold, and twofold axes of rotational symmetry.
These axes are perpendicular to the plane of the page and pass through the centers of each figure. Both polyhedral upper and spherical lower forms more Viruses were first found to have symmetry by x-ray diffraction studies and subsequently by electron microscopy with negative-staining techniques. In most icosahedral viruses, the protomers, i. The arrangement of capsomeres into an icosahedral shell compare Fig. This requires the identification of the nearest pair of vertex capsomeres called penton: Figure Adenovirus after negative stain electron microscopy.
A The capsid reveals the typical isometric shell made up from 20 equilateral triangular faces. The net axes are formed by lines of the closest-packed neighboring capsomeres.
In adenoviruses, the h and k axes also coincide with the edges of the triangular faces. The capsomere number C can be determined to be from the h and k indices and the equation: This symmetry and number of capsomeres is typical of all members of the adenovirus family. Virus Core Structure Except in helical nucleocapsids, little is known about the packaging or organization of the viral genome within the core. Small virions are simple nucleocapsids containing 1 to 2 protein species.
The larger viruses contain in a core the nucleic acid genome complexed with basic protein s and protected by a single- or double layered capsid consisting of more than one species of protein or by an envelope Fig.
Two-dimensional diagram of HIV-1 correlating immuno- electron microscopic findings with the recent nomenclature for the structural components in a 2-letter code and with the molecular weights of the virus structural glyco- proteins. SU stands for more Because of the error rate of the enzymes involved in RNA replication, these viruses usually show much higher mutation rates than do the DNA viruses. Mutation rates of lead to the continuous generation of virus variants which show great adaptability to new hosts.
The viral RNA may be single-stranded ss or double-stranded dsand the genome may occupy a single RNA segment or be distributed on two or more separate segments segmented genomes.
In addition, the RNA strand of a single-stranded genome may be either a sense strand plus strandwhich can function as messenger RNA mRNAor an antisense strand minus strandwhich is complementary to the sense strand and cannot function as mRNA protein translation see Ch. Sense viral RNA alone can replicate if injected into cells, since it can function as mRNA and initiate translation of virus-encoded proteins.
Antisense RNA, on the other hand, has no translational function and cannot per se produce viral components.
Figure Schemes of 21 virus families infecting humans showing a number of distinctive criteria: Each segment consists of a complementary sense and antisense strand that is hydrogen bonded into a linear ds molecule. The replication of these viruses is complex; only the sense RNA strands are released from the infecting virion to initiate replication.
The retrovirus genome comprises two identical, plus-sense ssRNA molecules, each monomer 7—11 kb in size, that are noncovalently linked over a short terminal region.
Retroviruses contain 2 envelope proteins encoded by the env-gene, 4—6 nonglycosylated core proteins and 3 non-structural functional proteins reverse transcriptase, integrase, protease: This DNA, mediated by the viral integrase, becomes covalently bonded into the DNA of the host cell to make possible the subsequent transcription of the sense strands that eventually give rise to retrovirus progeny.Capsid
After assembly and budding, retroviruses show structural and functional maturation. In immature virions the structural proteins of the core are present as a large precursor protein shell. After proteolytic processing by the viral protease the proteins of the mature virion are rearranged and form the dense isometric or cone-shaped core typical of the mature virion, and the particle becomes infectious.
The papovaviruses, comprising the polyoma- and papillomaviruses, however, have circular DNA genomes, about 5. Three or 2 structural proteins make up the papovavirus capsid: Single-stranded linear DNA, 4—6 kb in size, is found with the members of the Parvovirus family that comprises the parvo- the erythro- and the dependoviruses.
The virion contains 2—4 structural protein species which are differently derived from the same gene product see Ch. The adeno-associated virus AAV, a dependovirus is incapable of producing progeny virions except in the presence of helper viruses adenovirus or herpesvirus.
It is therefore said to be replication defective. Circular single-stranded DNA of only 1.