Cowpea Chlorotic Mottle Virus
Encyclopedia
Cowpea Chlorotic Mottle Virus, known by the abbreviation CCMV, is a virus
that specifically infects the cowpea plant, or black-eyed pea
. The leaves of infected plants develop yellow spots, hence the name "chlorotic". Similar to its "brother" virus, Cowpea mosaic virus
(CPMV), CCMV is produced in high yield in plants. In the natural host, viral particles can be produced at 1-2mg per gram of infected leaf tissue. Like the majority of viruses, CCMV consists of a protein shell, that surrounds a central core of RNA
. Its protein shell, or capsid
, is composed of icosahedral arrangements of identical protein subunits. The symmetry at which this is done is exactly like the symmetry of a football: hexagons and pentagon
s are interchanged to give the final sphere. The virus is about 30 nm in size, and can be observed with transmission electron microscopy
using negative staining.
and with relatively high amounts of salts, it is possible to stimulate the self-assembly
of the protein subunits, into a shell of identical size to the virus. This yields an empty capsid which has a number of interesting properties. Several successful attempts are reported to incorporate other materials, such as inorganic crystals, inside the capsid.
Some of the physical properties of CCMV are: toleration of high temperatures, a variety of pH's, and stability in organic solvents, such as DMSO
. These conditions allow for a wide range of chemistry to be tolerated in CCMV modification. One of the most profound characteristics of CCMV is that the viral capsid can undergo reversible pH and metal-ion structural transition, without any loss of viral function or structural damage. This transition, referred to as "swelling," forms 60 separate 2nm sized openings in the protein shell. Opening of the cavity occurs under slightly acidic conditions at a pH of about 6.5. The capsule can be closed by reversing the pH to about 5.0. The swollen capsid permits ions to diffuse freely into and out of the cavity. Entrapment of organic or inorganic materials is only restricted by the interactions of these molecules with molecules of the viral interior. The interior and exterior properties of the viral capsid are dissimilar enough to control the localization of molecules within the protein cage. The cationic interior would naturally encapsulate anionic species, but the charge of the cavity can be altered by site-directed mutagenesis.
Additionally, accessible amines and carboxylates representing potential sites for external modification have been identified on the exterior surface of the viral capsid. These groups can be modified to facilitate specific biological targeting or surface interactions through the linking of various ligands. Fluorescent dyes have also been shown to be selectively attached to the capsid surface.
As the virus' natural ability to infect host cells can be exploited, the use of CCMV is of novel interest to researchers. CCMV has feasible applications in biosensors, nanoelectric devices, and drug targeting and delivery.
Lastly, though CPMV exhibits similar physical properties to CCMV, CCMV has been shown to be more easily modified, less susceptible to degradation, and is not shown to be specific for particular mammalian cells in vivo.
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
that specifically infects the cowpea plant, or black-eyed pea
Black-eyed pea
The black-eyed pea, also called black-eyed bean and chawalie or lobia in various languages in India and Pakistan, is a subspecies of the cowpea, grown around the world for its medium-sized, edible bean. The bean mutates easily, giving rise to a number of varieties. The common commercial one is...
. The leaves of infected plants develop yellow spots, hence the name "chlorotic". Similar to its "brother" virus, Cowpea mosaic virus
Cowpea mosaic virus
Cowpea mosaic virus is a plant virus of the comovirus group. Infection of a susceptible cowpea leaf results in high virus yields . Its Genome consists of 2 molecules of positive-sense RNA which are separately encapsidated. Both RNA1 and RNA2 have a VPg at the 5'end, and polyadenylation at the...
(CPMV), CCMV is produced in high yield in plants. In the natural host, viral particles can be produced at 1-2mg per gram of infected leaf tissue. Like the majority of viruses, CCMV consists of a protein shell, that surrounds a central core of RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
. Its protein shell, or capsid
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
, is composed of icosahedral arrangements of identical protein subunits. The symmetry at which this is done is exactly like the symmetry of a football: hexagons and pentagon
Pentagon
In geometry, a pentagon is any five-sided polygon. A pentagon may be simple or self-intersecting. The sum of the internal angles in a simple pentagon is 540°. A pentagram is an example of a self-intersecting pentagon.- Regular pentagons :In a regular pentagon, all sides are equal in length and...
s are interchanged to give the final sphere. The virus is about 30 nm in size, and can be observed with transmission electron microscopy
Transmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
using negative staining.
History
Bancroft et al. in 1967 described the first experiments to isolate and characterise the virus. Since that time, due to the relative ease with which it is grown and isolated, many researchers have focused their attention on the virus. The interest of the scientific community for this virus is also due to a conspicuous property: it is possible to disassemble the virus and remove the genetic material, the RNA. Then, under slightly acidic pHPH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
and with relatively high amounts of salts, it is possible to stimulate the self-assembly
Self-assembly
Self-assembly is a term used to describe processes in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction...
of the protein subunits, into a shell of identical size to the virus. This yields an empty capsid which has a number of interesting properties. Several successful attempts are reported to incorporate other materials, such as inorganic crystals, inside the capsid.
The promise of CCMV in nanotechnology
CCMV has a number of physical properties that can be exploited for nanoscale fabrications. As previously stated, viruses consist of a protein coat, called a capsid, and nucleic acid (either RNA or DNA). The capsid's main function is to protect the nucleic acid. Mutagenesis of viral capsids is a well-established technique that permits the alteration of the capsid surface. Such alterations can include changing the charge or attaching specific ligands to the capsid surface via their chemical interactions with surface molecules or amino acids. Viral capsids have been shown to allow the attachment of small peptides (<30 amino acids) onto their surface. Furthermore, heterologous expression of CCMV in yeast allows large-scale production of wild-type or genetically modified CCMV capsids. These capsids can either contain or be empty of nucleic acid. Without nucleic acid, these cage-like structures provide cavities of well-defined size, shape, and charge, and can be used for particle-specific entrapment of organic and inorganic materials.Some of the physical properties of CCMV are: toleration of high temperatures, a variety of pH's, and stability in organic solvents, such as DMSO
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...
. These conditions allow for a wide range of chemistry to be tolerated in CCMV modification. One of the most profound characteristics of CCMV is that the viral capsid can undergo reversible pH and metal-ion structural transition, without any loss of viral function or structural damage. This transition, referred to as "swelling," forms 60 separate 2nm sized openings in the protein shell. Opening of the cavity occurs under slightly acidic conditions at a pH of about 6.5. The capsule can be closed by reversing the pH to about 5.0. The swollen capsid permits ions to diffuse freely into and out of the cavity. Entrapment of organic or inorganic materials is only restricted by the interactions of these molecules with molecules of the viral interior. The interior and exterior properties of the viral capsid are dissimilar enough to control the localization of molecules within the protein cage. The cationic interior would naturally encapsulate anionic species, but the charge of the cavity can be altered by site-directed mutagenesis.
Additionally, accessible amines and carboxylates representing potential sites for external modification have been identified on the exterior surface of the viral capsid. These groups can be modified to facilitate specific biological targeting or surface interactions through the linking of various ligands. Fluorescent dyes have also been shown to be selectively attached to the capsid surface.
As the virus' natural ability to infect host cells can be exploited, the use of CCMV is of novel interest to researchers. CCMV has feasible applications in biosensors, nanoelectric devices, and drug targeting and delivery.
Lastly, though CPMV exhibits similar physical properties to CCMV, CCMV has been shown to be more easily modified, less susceptible to degradation, and is not shown to be specific for particular mammalian cells in vivo.