This domain pair constitutes a superdomain, a heritable unit that is found in various proteins in fungi, plants and animals.

[4] In addition, phosphatidylinositol 3-kinase (PI3-kinase), an enzyme that phosphorylates phosphoinositides on the 3-hydroxyl group of the inositol ring, also uses a C2 domain to bind to the membrane (e.g. 1e8w PDB entry).

The C2 domain is thought to be involved in calcium-dependent phospholipid binding[7] and in membrane targeting processes such as subcellular localisation.

[8] The domain forms an eight-stranded beta sandwich constructed around a conserved 4-stranded motif, designated a C2 key.

[9] Calcium binds in a cup-shaped depression formed by the N- and C-terminal loops of the C2-key motif.