IMGT®, the international ImMunoGeneTics information system®

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:

• - the V-DOMAIN (V for variable)
• - the C-DOMAIN (C for constant)
• - the G-DOMAIN (G for groove)
• - the V-LIKE-DOMAIN
• - the C-LIKE-DOMAIN
• - the G-LIKE-DOMAIN

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.

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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:

• VH (V-DOMAIN of an IG-Heavy chain)
• VL (V-DOMAIN of an IG-Light chain)
• V-KAPPA (V-DOMAIN of an IG-Light-Kappa chain)
• V-LAMBDA (V-DOMAIN of an IG-Light-Lambda chain)
• V-ALPHA (V-DOMAIN of a TR-Alpha chain)
• V-BETA (V-DOMAIN of a TR-Beta chain)
• V-GAMMA (V-DOMAIN of a TR-Gamma chain)
• V-DELTA (V-DOMAIN of a TR-Delta chain)

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.

• The C-DOMAIN corresponds to the complete C-REGION in the case of an IG-Light chain. This single C-DOMAIN is designated as:
  • CL (C-DOMAIN of an IG-Light chain)
  • C-KAPPA (C-DOMAIN of an IG-Light-Kappa chain)
  • C-LAMBDA (C-DOMAIN of an IG-Light-Lambda chain)
  • C-IOTA (C-DOMAIN of an IG-Light-Iota chain)
• The C-DOMAIN corresponds to most of the C-REGION in the case of a T cell receptor chain. This single C-DOMAIN is designated as:
  • C-ALPHA (C-DOMAIN of a TR-Alpha chain)
  • C-BETA (C-DOMAIN of a TR-Beta chain)
    • C-BETA-1 (C-DOMAIN of a TR-Beta-1 chain)
    • C-BETA-2 (C-DOMAIN of a TR-Beta-2 chain)
  • C-GAMMA (C-DOMAIN of a TR-Gamma chain)
    • C-GAMMA-1 (C-DOMAIN of a TR-Gamma-1 chain)
    • C-GAMMA-2 (C-DOMAIN of a TR-Gamma-2 chain)
  • C-DELTA (C-DOMAIN of a TR-Delta chain)

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 C-DOMAIN corresponds to only part of the C-REGION in the case of an IG-Heavy chain. Indeed, an IG-Heavy chain consists of several C-DOMAIN (from 3 to 7). These C-DOMAIN are designated as CH and comprise:
  • CH1 (C-DOMAIN corresponding to the CH1 exon of an IG-Heavy chain)
  • CH2 (C-DOMAIN corresponding to the CH2 exon of an IG-Heavy chain)
  • CH3 (C-DOMAIN corresponding to the CH3 exon of an IG-Heavy chain)
  • CH4 (C-DOMAIN corresponding to the CH4 exon of an IG-Heavy chain)
  • CH5 (C-DOMAIN corresponding to the CH5 exon of an IG-Heavy chain)
  • CH6 (C-DOMAIN corresponding to the CH6 exon of an IG-Heavy chain)
  • CH7 (C-DOMAIN corresponding to the CH7 exon of an IG-Heavy chain)
  The CH name may also include, if necessary, information on the chain type, for instance, CH1-GAMMA-1.
  In addition to the C-DOMAIN, an IG-Heavy chain may comprise regions which are not part of the C-DOMAIN, the HINGE-REGION (for the IG-Heavy-Alpha, IG-Heavy-Delta and IG-Heavy-Gamma chains), and
  • for the membrane form: the CONNECTING-REGION, the TRANSMEMBRANE-REGION and the CYTOPLASMIC-REGION
  • for the soluble form: the CHS.

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.

• The G-DOMAIN are designated as:
  • G-ALPHA1 (G-DOMAIN corresponding to domain 1 of a MH1-Alpha chain)
  • G-ALPHA2 (G-DOMAIN corresponding to domain 2 of a MH1-Alpha chain)
  • G-ALPHA (G-DOMAIN of a MH2-Alpha chain)
  • G-BETA (G-DOMAIN of a MH2-Beta chain)

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.

• The G-LIKE-DOMAIN are designated as:
  • G-ALPHA1-LIKE (G-LIKE-DOMAIN corresponding to domain 1 of a RPI-MH1Like-Alpha chain)
  • G-ALPHA2-LIKE (G-LIKE-DOMAIN corresponding to domain 2 of a RPI-MH1Like-Alpha chain)

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".