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.