TAP-associated glycoprotein, also known as tapasin or TAPBP, is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that in humans is encoded by the ''TAPBP''
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
.
Function
The ''TAPBP'' gene encodes a transmembrane
glycoprotein
Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known a ...
that mediates interaction between newly assembled major histocompatibility complex (
MHC)
class I molecules and the transporter associated with antigen processing (TAP), which is required for the transport of antigenic peptides across the
endoplasmic reticulum
The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...
membrane. This interaction facilitates optimal peptide loading on the MHC class I molecule. Up to four complexes of MHC class I and tapasin may be bound to a single TAP molecule. Tapasin contains a
C-terminal
The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, carboxy tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When t ...
double-lysine motif (KKKAE) known to maintain membrane proteins in the endoplasmic reticulum. In humans, the tapasin gene lies within the major histocompatibility complex on chromosome 6. Alternative splicing results in three transcript variants encoding different isoforms.
Tapasin is a MHC class I
antigen
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
...
-processing
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
present in the lumen of the endoplasmic reticulum. It plays an important role in the maturation of MHC class I molecules in the ER lumen. Tapasin is one component of the peptide-loading complex, and can be found associated with MHC class I molecules after the MHC class I heavy chain has associated with Beta
2 microglobulin. The peptide-loading complex consists of TAP, tapasin, MHC class I,
calreticulin
Calreticulin also known as calregulin, CRP55, CaBP3, calsequestrin-like protein, and endoplasmic reticulum resident protein 60 (ERp60) is a protein that in humans is encoded by the ''CALR'' gene.
Calreticulin is a multifunctional soluble prot ...
, and ERp57. Tapasin recruits MHC class I molecules to the TAP peptide transporter, and also enhances loading of MHC class I with high-affinity
peptides
Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Dalton (unit), Da or more are called proteins. Chains of fewer t ...
. Following loading of MHC class I with a high-affinity ligand, the interaction between tapasin and MHC class I disappears.
Interactions
Tapasin has been shown to
interact with:
*
HLA-A
HLA-A is a group of human leukocyte antigens (HLA) that are encoded by the ''HLA-A'' locus (genetics), locus, which is located at human chromosome 6p21.3. HLA is a major histocompatibility complex (MHC) antigen specific to humans. HLA-A is one o ...
,
[ and
* TAP1]
See also
* Transporter associated with antigen processing
Transporter associated with antigen processing (TAP) protein complex belongs to the ATP-binding-cassette transporter family. It delivers cytosolic peptides into the endoplasmic reticulum (ER), where they bind to nascent MHC class I molecules.
T ...
("TAP")
References
Further reading
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External links
* {{MeshName, tapasin
PDBe-KB
provides an overview of all the structure information available in the PDB for Human Tapasin