Immunoglobulin superfamily

The term "immunoglobulin superfamily" (IgSF) is defined differently from the term "protein superfamily". In general, this term is used to describe a group of different (glyco-) proteins that have been highly conserved during evolution. IgSF are found in both vertebrates and non-vertebrates, but also in yeasts. In humans, the immunoglobulin superfamily represents the most extensive group of all superfamilies (765 representatives in the human genome).

A structural characteristic of the members of this family is a domain of 70-110 aminoacyl residues which is also found in immunoglobulins.

This domain is characterized by a (special) beta leaflet structure (it is analogous to the folded structure of immunoglobulins). This similarly shaped construction principle, with an identical three-dimensional construct, is important for the non-enzymatic surface recognition of antigens. The middle segments of the β leaflets, which are placed in a sandwich position, are linked by a disulfide bond. This ensures their stability.

Depending on the similarity of the IgSFs with the variable region or with the constant region of an immunoglobulin, the IgSF domains are differentiated into V-like (variable structure) or C-like (constant structure).

In contrast to the soluble immunoglobulins themselves, most members of the Ig superfamily are found on cell surfaces where they are involved in cell-cell interactions and thus influence immunological processes.

Members of the immunoglobulin superfamily are immunoglobulins, killer cell immunoglobulin-like receptor, most Fc-receptors, CD3-receptor, T-cell receptor, myelin-oligodendrocyte glycoprotein, the B-lymphocyte antigen CD19, Cell adhesion molecules (CAMs and JAMs) such as the neural cell adhesion molecule 1 also called NKAM-1 or CD56 (Tan RPA et al 2017), the herpes virus entry mediator Nectin-1, ICAM or the sialic acid-binding immunoglobulin-like lectins = Siglecs (Ono E et al. 2018), CD31,(CD33), CD66a, CD66b, CD66c, CD66d, CD66e, CD66f, CD80, CD86, CD90, CD96 and CD155.

Herpes viruses, smallpox viruses and adenoviruses form inhibitory variants of various members of the immunoglobulin superfamily, e.g. CD200, CD47, Interleukin-1 receptor 2, Interleukin-18 binding protein, CD80, CEA-related cell adhesion molecules, (Farré D et al. 2017).

The name leaflet is derived from the three-dimensional structure of the beta leaflet, whose corrugated sheet-like form resembles a regularly folded sheet of paper.

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