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Chain type

The 'chain type' concept identifies the type of a polypeptide chain.

The 'chain type' concept is part of the 'IDENTIFICATION' concept of IMGT-ONTOLOGY [1]

In IMGT, the 'chain type' concept identifies the type of the polypeptide chain potentially encoded by the Immunoglobulin (IG), T cell receptor (TR) and major histocompatibility complex (MHC) genes.

The 'chain type' concept has been extended to the chains of the related proteins of the immune system (RPI) and of the fusion proteins of immune applications (FPIA).

Click here for a list of the IG, TR and MHC chain types and for examples of RPI and FPIA, in IMGT/PROTEIN-DB and IMGT/3Dstructure-DB. This table also provides the standardized labels used in the 2D or 3D structure organization of IG, TR and MHC chains.

Immunoglobulins (IG)

The 'chain type' concept for the immunoglobulins (IG) includes two broad concepts:

An IG 'chain type' is identified by its constant region (C-REGION) which is encoded by a constant gene (C-GENE).

The number of IG chain types instances, in a species, depends from the number of functional IG C-GENEs per haplotype.

There are eleven instances for the IG 'chain type', in human:

T cell receptors (TR)

The 'chain type' concept for the T cell receptors (TR) includes four main concepts:

A TR 'chain type' is identified by its constant region (C-REGION) which is encoded by a constant gene (C-GENE).

The number of TR chain types instances, in a species, depends from the number of functional TR C-GENEs per haplotype.

There are six instances for the TR 'chain type', in human:

Major histocompatibility complex (MHC)

The 'chain type' concept for the major histocompatibility complex (MHC) identifies the nature of the polypeptide chain potentially encoded by the MHC genes (classical MHC-Ia and MHC-IIa, and nonclassical MHC-Ib and MHC-IIb) and, by extension, by the B2M gene, the Beta2-Microglobulin chain being associated to the MHC-Ia-Alpha and to the MHC-Ib-Alpha chains.

The 'chain type' concept for the Major histocompatibility complex (MHC) includes six main concepts:

The number of MHC chain types instances, in a species, depends on the number of functional MHC genes per haplotypes.

Related proteins of the immune system (RPI)

The 'chain type' concept for the related proteins of the immune system (RPI) identifies chains in proteins other than IG, TR or MHC with a function in the immune system. Many of these proteins have at least one V-LIKE-DOMAIN or one C-LIKE-DOMAIN and, in that case, belongs to the IgSF, or at least one G-LIKE-DOMAIN and which generally, but not necessarily, possess at least one LIKE-DOMAIN (V-, C- or G-). Some MHC-I-like chains are not associated with the Beta2-Microglobulin.
Example: MICA pdf

IMGT note:
(1) Several IG-Light-Lambda chain types are encoded by different IGLC genes.
Reference:
[1] Giudicelli, V. and Lefranc, M.-P., Bioinformatics, 15, 1047-1054 (1999) PMID: 10745995, LIGM:221 pdf
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