The immunoglobulin superfamily (IgSF) is a large group of proteins that have a similar tertiary structure, the immunoglobulin fold, which is a beta-sandwich that can have a varying number of strands. These largely carry out functions in the immune system, in cell-cell recognition or in structural organization of muscle. First detected by sequence homology, it has since been verified experimentally that they all have this sandwich structure. IgSF proteins are all about 100 amino acids long and contain a conserved disulfide packed against a tryptophan. This central structure motif is also known as 'the pin'.

All antibodies are made up of several Ig domains (such as Immunoglobulin E (IgE). They are also a central component in many extracellular domains of cell surface receptors.

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