InterPro: IPR003596 Immunoglobulin V-set, subgroup

The basic structure of immunoglobulin (Ig) molecules is a tetramer of two light chains and two heavy chains linked by disulphide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains: alpha, delta, epsilon, gamma and mu, all consisting of a variable domain (VH) and three (in alpha, delta and gamma) or four (in epsilon and mu) constant domains (CH1 to CH4). Ig molecules are highly modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. The domains in Ig and Ig-like molecules are grouped into four types: V-set (variable; IPR013106), C1-set (constant-1; IPR003597), C2-set (constant-2; IPR008424) and I-set (intermediate; IPR013098) [1]. Structural studies have shown that these domains share a common core Greek-key beta-sandwich structure, with the types differing in the number of strands in the beta-sheets as well as in their sequence patterns [2, 3].

Immunoglobulin-like domains that are related in both sequence and structure can be found in several diverse protein families. Ig-like domains are involved in a variety of functions, including cell-cell recognition, cell-surface receptors, muscle structure and the immune system [4].

Ig-like domains can be classified according to the number of beta strands. The V-type is antibody variable domain-like, and has two extra beta strands over the classical C1-type Ig-like domain. This subfamily includes Ig variable domains, myelin membrane adhesion molecules, T cell surface glycoproteins, junction adhesion molecules (JAM), coxsackie virus and adenovirus Car receptors, and viral haemagglutinin.