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DOMAIN

The 'DOMAIN' concept describes a subunit of a chain characterized by its three-dimensional (3D) structure.

The 'DOMAIN' concept is part of the 'DESCRIPTION' concept of IMGT-ONTOLOGY [1]

In IMGT, the 'DOMAIN' concept includes 6 main concepts:

V-DOMAIN and C-DOMAIN are found in immunoglobulin (IG) and T cell receptor (TR) chains.
G-DOMAIN are found in major histocompatibility (MH) chains.
V-LIKE-DOMAIN and C-LIKE-DOMAIN are found in IgSF chains other than IG or TR.
G-LIKE-DOMAIN are found in MhSF chains other than MH.

Correspondence between 'DOMAIN' (DESCRIPTION) and 'DomainType' (IDENTIFICATION) concepts
'DOMAIN' 'DomainType'
  • V-DOMAIN (IG and TR)
  • V-LIKE-DOMAIN (IgSF other than IG and TR)
V
  • C-DOMAIN (IG and TR)
  • C-LIKE-DOMAIN (IgSF other than IG and TR)
C
  • G-DOMAIN (MH)
  • G-LIKE-DOMAIN (MhSF other than MH)
G
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Correspondence between labels for IG and TR domains in IMGT/3Dstructure-DB and IMGT/LIGM-DB
IMGT unique numbering for V-DOMAIN and V-LIKE-DOMAIN [2]
IMGT unique numbering for C-DOMAIN and C-LIKE-DOMAIN [3]
IMGT unique numbering for G-DOMAIN and G-LIKE-DOMAIN [4]

V-DOMAIN and C-DOMAIN

An immunoglobulin or T cell receptor chain usually consists of one V-DOMAIN and one or several C-DOMAIN(s).

The V-DOMAIN corresponds to the V-J-REGION or V-D-J-REGION of the immunoglobulin or T cell receptor chain. This single V-DOMAIN is designated as:

The C-DOMAIN corresponds to the complete C-REGION, to most of the C-REGION or to only part of the C-REGION, depending on the immunoglobulin or T cell receptor chain type.

In addition to the C-DOMAIN, a TR chain comprises a CONNECTING-REGION, a TRANSMEMBRANE-REGION and a CYTOPLASMIC-REGION, which are not part of the C-DOMAIN.

The molecular structure of the immunoglobulin chains in domains (12 for IgG, IgD and IgA, 14 for IgM and IgE) is extensively used for the construction and expression of engineered antibodies.

G-DOMAIN

A MH class I (MH1) protein comprises one alpha chain and one Beta2-Microglobulin (B2M) chain. The MH1 alpha chain consists of three domains: domains 1 and 2 are G-DOMAIN and domain 3 is a C-LIKE-DOMAIN. The B2M chain consists of a single C-LIKE-DOMAIN.

A MH class II (MH2) protein comprises one alpha chain and one beta chain. Each chain consists of two domains: domain 1 is a G-DOMAIN and domain 2 is a C-LIKE-DOMAIN.

V-LIKE-DOMAIN and C-LIKE-DOMAIN

A V-LIKE-DOMAIN corresponds to a domain of similar 3D structure as the V-DOMAIN, for IgSF proteins other than IG or TR.

A C-LIKE-DOMAIN corresponds to a domain of similar 3D structure as the C-DOMAIN, for IgSF proteins other than IG or TR.

G-LIKE-DOMAIN

A G-LIKE-DOMAIN corresponds to a domain of similar 3D structure as the G-DOMAIN, for MhSF proteins other than MH.

Proteins other than MH which have been found with G-LIKE-DOMAIN are so far of the MH1Like type. These chains and the corresponding genes were previously referred to as "MH-like", "MH-I-like" or "MH-I-Alpha-like".

References:
[1] Giudicelli, V. and Lefranc, M-P., Bioinformatics, 15, 1047-1054 (1999) PMID: 10745995, LIGM:221 pdf
[2] Lefranc, M.-P. et al., Dev. Comp. Immunol., 27, 55-77 (2003) PMID: 12477501 LIGM:268 pdf
[3] Lefranc, M.-P. et al., Dev. Comp. Immunol., 29, 185-203 (2005) PMID: 15572068 LIGM:293 pdf
[4] Lefranc, M.-P. et al., Dev. Comp. Immunol., 2005, 29, 917-938 PMID: 15936075 LIGM: 296 pdf