T Cell Receptors

What InterPro Tells Us:

Types of T Cell Receptors

There are two types pf TCRs, a/b-type and g/d-type. The a/b-type TCRs are heterodimers composed of two chains, designated a and b, where each chain consists of a constant region and a variable region, the latter containing three hypervariable regions that participate in antigen binding. The sequence variability found in the variable region occurs as a result of the high frequency of recombination undergone by the gene cluster encoding this region, which can yield as many as 2.5 x 10⁷ possible variants. The cytotoxic T lymphocytes, helper T cells and inflammatory T cells discussed in here all bare a/b-type TCRs. The a/b-type can only bind to epitopes bound to MHC molecules presented on the surface of cells.

The g/d TCRs are also heterodimers composed of two chains, designated g and d, encoded by different gene segments. Unlike a/b-type TCRs, the g/d receptors can bind to free intact proteins in a similar manner to that of antibody binding. T cells that possess g/d TCRs are usually located in the epithelia, where they may represent an early defence system against pathogens.

P01738 Mouse T-cell receptor alpha chain V region

InterPro Domain Architecture

InterPro Entry	Method Accession	Graphical Match	Method Name
IPR003596	SM00406		IGv
IPR007110	PS50835		IG_LIKE
Classification	PDB Chain/Domain ID	PDB Chain/Structural Domains
1mwa	1mwaa
1mwa	1mwac

From the graphical match above, you can see that the signatures (method accession) are divided into two InterPro entries for mouse T-cell receptor a chain V region. These entries give information about the domain architecture of the protein. IPR007110 represents the Immunoglobulin-like domain, which here has one signature, PS50835 from the PROSITE database. This is a very large class of domain that includes not only immunoglobulins themselves, but also any protein that has a domain resembling the immunoglobulin domain in terms of sequence and beta-sandwich structure. If you follow the links to IPR007110, you will find that there are several InterPro families listed under the section labelled ‘Children’, where the ‘Children’ represent different subgroups of immunoglobulin-like domains. To find all the domain subgroups covered by the immunoglobulin-like domain entry, you can either follow the individual links to the different InterPro entries, or you can follow the link labelled ‘[tree]’ found directly underneath the ‘Children’ tag (or follow the link provided here).

Mouse T-cell receptor a chain V region belong to IPR003596, the Immunoglobulin V-type domain, which is represented by one signature, SM00406 from the SMART database.

The remaining two entries in the table above are from the structural database PDB (1mwa). From the information in the table above, you can see that there are two chains in this structure that represent this domain, chain A (1mwaa) and chain C (1mwac).

What the Structure Tells Us

There are structures available for T cell receptors from several different species in the Protein Data Bank (PDB). A detailed description and visualisation of the structural features of T cell receptors can be found at the PDB ‘Molecule of the Month’. The crystallographic structures of different TCRs have provided insight into the mechanism of action of these receptors.

Next: Table of T Cell Receptor Proteins

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