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T-cell antigen receptors

TCRComplex.png
The T-cell receptor complex with TCR-α and TCR-β chains, CD3 and ζ-chain accessory molecules.
Identifiers
Symbol TCR_zetazeta
Pfam PF11628
InterPro IPR021663
OPM superfamily 261
OPM protein 2hac
T-cell receptor alpha locus
Identifiers
Symbol TRA
Alt. symbols TCRA, TRA@
Entrez 6955
HUGO 12027
OMIM 186880
Other data
Locus Chr. 14 q11.2
T-cell receptor beta locus
Identifiers
Symbol TRB
Alt. symbols TCRB, TRB@
Entrez 6957
HUGO 12155
OMIM 186930
Other data
Locus Chr. 7 q34
T-cell receptor delta locus
Identifiers
Symbol TRD
Alt. symbols TCRD, TRD@, TCRDV1
Entrez 6964
HUGO 12252
Other data
Locus Chr. 14 q11.2
T-cell receptor gamma locus
Identifiers
Symbol TRG
Alt. symbols TCRG, TRG@
Entrez 6965
HUGO 12271
Other data
Locus Chr. 7 p14

The T-cell receptor, or TCR, is a molecule found on the surface of T cells, or T lymphocytes, that is responsible for recognizing fragments of antigen as peptides bound to (MHC) molecules. The binding between TCR and antigen peptides is of relatively low affinity and is degenerate: that is, many TCRs recognize the same antigen peptide and many antigen peptides are recognized by the same TCR.

The TCR is composed of two different protein chains (that is, it is a heterodimer). In humans, in 95% of T cells the TCR consists of an alpha (α) chain and a beta (β) chain (encoded by TRA and TRB, respectively), whereas in 5% of T cells the TCR consists of gamma and delta (γ/δ) chains (encoded by TRG and TRD, respectively). This ratio changes during ontogeny and in diseased states (such as leukemia). It also differs between species. Orthologues of the 4 loci have been mapped in various species. Each locus can produce a variety of polypeptides with constant and variable regions.

When the TCR engages with antigenic peptide and MHC (peptide/MHC), the T lymphocyte is activated through signal transduction, that is, a series of biochemical events mediated by associated enzymes, co-receptors, specialized adaptor molecules, and activated or released transcription factors.

The TCR is a disulfide-linked membrane-anchored heterodimeric protein normally consisting of the highly variable alpha (α) and beta (β) chains expressed as part of a complex with the invariant CD3 chain molecules. T cells expressing this receptor are referred to as α:β (or αβ) T cells, though a minority of T cells express an alternate receptor, formed by variable gamma (γ) and delta (δ) chains, referred as γδ T cells.


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