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CD8 (cluster of differentiation
Cluster of differentiation

The cluster of differentiation is a protocol used for the identification and investigation of cell surface molecules present on leukocytes. CD molecules can act in numerous ways, often acting as receptor or ligand important to the cell....
 8) is a transmembrane
Transmembrane protein

A transmembrane protein is a protein that spans the entire biological membrane. Transmembrane proteins aggregate and precipitate in water. They require detergents or nonpolar solvents for extraction, although some of them can be also extracted using denaturing agents....
 glycoprotein
Glycoprotein

Not to be confused with peptidoglycan or proteoglycan.Glycoproteins are proteins that contain oligosaccharide chains covalently attached to their Peptide side-chains....
 that serves as a co-receptor
Co-receptor

A co-receptor is a cell surface receptor that binds a signalling molecule in addition to a primary receptor in order to facilitate ligand recognition and initiate a biological process, such as entry of a pathogen into a host cell....
 for the T cell receptor
T cell receptor

The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is, in general, responsible for recognizing antigens bound to major histocompatibility complex molecules....
 (TCR). Like the TCR, CD8 binds to a major histocompatibility complex
Major histocompatibility complex

The major histocompatibility complex is a large genome region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system, autoimmunity, and reproduction success....
 (MHC) molecule, but is specific for the class I MHC
Major histocompatibility complex

The major histocompatibility complex is a large genome region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system, autoimmunity, and reproduction success....
 protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene. In humans, both genes are located on chromosome 2 in position 2p12.

Structure
To function, CD8 forms a dimer, consisting of a pair of CD8 chains.






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Encyclopedia


CD8 (cluster of differentiation
Cluster of differentiation

The cluster of differentiation is a protocol used for the identification and investigation of cell surface molecules present on leukocytes. CD molecules can act in numerous ways, often acting as receptor or ligand important to the cell....
 8) is a transmembrane
Transmembrane protein

A transmembrane protein is a protein that spans the entire biological membrane. Transmembrane proteins aggregate and precipitate in water. They require detergents or nonpolar solvents for extraction, although some of them can be also extracted using denaturing agents....
 glycoprotein
Glycoprotein

Not to be confused with peptidoglycan or proteoglycan.Glycoproteins are proteins that contain oligosaccharide chains covalently attached to their Peptide side-chains....
 that serves as a co-receptor
Co-receptor

A co-receptor is a cell surface receptor that binds a signalling molecule in addition to a primary receptor in order to facilitate ligand recognition and initiate a biological process, such as entry of a pathogen into a host cell....
 for the T cell receptor
T cell receptor

The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is, in general, responsible for recognizing antigens bound to major histocompatibility complex molecules....
 (TCR). Like the TCR, CD8 binds to a major histocompatibility complex
Major histocompatibility complex

The major histocompatibility complex is a large genome region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system, autoimmunity, and reproduction success....
 (MHC) molecule, but is specific for the class I MHC
Major histocompatibility complex

The major histocompatibility complex is a large genome region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system, autoimmunity, and reproduction success....
 protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene. In humans, both genes are located on chromosome 2 in position 2p12.

Tissue distribution


The CD8 co-receptor is predominantly expressed on the surface of cytotoxic T cell
Cytotoxic T cell

A cytotoxic T cell belongs to a sub-group of T cells that are capable of inducing the death of infection somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or dysfunctional....
s, but can also be found on natural killer cell
Natural killer cell

Natural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses....
s.

Structure


To function, CD8 forms a dimer, consisting of a pair of CD8 chains. The most common form of CD8 is composed of a CD8-a and CD8-ß chain, both members of the immunoglobulin superfamily
Immunoglobulin superfamily

The immunoglobulin superfamily is a large group of cell surface and soluble proteins that are involved in the recognition, binding, or cell adhesion processes of Cell ....
 with an immunoglobulin variable (IgV)-like
Immunoglobulin fold

An immunoglobulin fold is a common all-? protein fold that consists of a 2-layer sandwich of ~7 antiparallel beta sheet arranged in two beta sheet....
 extracellular domain connected to the membrane by a thin stalk, and an intracellular tail. Less-common homodimers of the CD8-a chain are also expressed on some cells. The molecular weight of CD8 is about 13,463.2 Da. Structure of the CD8 molecule was determined by Leahy, D.J., Axel, R., and Hendrickson, W.A. by X-ray Diffraction at a 2.6A resolution. The structure was determined to have an immunoglobulin-like beta-sandwich folding and 114 amino acid residues. 2% of the protein is wound into a-helices and 46% into ß-sheets, with the remaining 52% of the molecules remaining in the loop portions.
Cd8 Receptor

Function


The extracellular IgV-like domain of CD8-a interacts with to the a3 portion of the Class I MHC molecule. This affinity keeps the T cell receptor
T cell receptor

The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is, in general, responsible for recognizing antigens bound to major histocompatibility complex molecules....
 of the cytotoxic T cell and the target cell bound closely together during antigen-specific activation. Cytotoxic T cells with CD8 surface protein are called CD8+ T cells. The main recognition site is a flexible loop at the a3 domain of an MHC molecule. This was discovered by doing mutational analyses. The flexible a3 domain is located between residues 223 and 229 in the genome.