IMGT Unique Numbering for the Variable (V), Constant (C), and Groove (G) Domains of IG, TR, MH, IgSF, and MhSF

INTRODUCTION The “IMGT unique numbering” (or “IMGTᵤniqueₙumbering”) concept is a major concept of numerotation (generated from the NUMEROTATION axiom) of IMGT-ONTOLOGY, the global reference in immunogenetics and immunoinformatics, built by IMGT, the international ImMunoGeneTics information system. The “IMGT unique numbering” concept, described here, allows one to number domain types that are characteristic of protein superfamilies, whatever the species, the molecule type or the chain type. Three leafconcepts (a leafconcept is a concept that corresponds to the finest level of granularity) have been defined, respectively, for the variable (V) domain and constant (C) domain of the immunoglobulin superfamily (IgSF) and for the groove (G) domain of the major histocompatibility (MH) superfamily (MhSF). The IMGT unique numbering concept has been a great breakthrough in immunogenetics and systems biology in allowing, for the first time, the bridging of the gap between amino acid (and nucleotide) sequences of any V, C, or G domain and their two-dimensional (2D) and three-dimensional (3D) structures. The IMGT unique numbering concept has been fundamental in the creation of the IMGT Collier de Perles and in the standardization of the description of mutations, amino acid changes, polymorphisms, and contact analysis in the IMGT databases, tools, and web resources.