Calcium-binding EGF domain
In molecular biology, the calcium-binding EGF domain is an EGF-like domain of about forty amino-acid residues found in epidermal growth factor (EGF). This domain is present in a large number of membrane-bound and extracellular, mostly animal, proteins. Many of these proteins require calcium for their biological function and a calcium-binding site has been found at the N-terminus of some EGF-like domains. Calcium-binding may be crucial for numerous protein-protein interactions. For human coagulation factor IX it has been shown that the calcium-ligands form a pentagonal bipyramid. The first, third and fourth conserved negatively charged or polar residues are side chain ligands. The latter is possibly hydroxylated. A conserved aromatic residue, as well as the second conserved negative residue, are thought to be involved in stabilising the calcium-binding site. As in non-calcium binding EGF-like domains, there are six conserved cysteines and the structure of both types is very similar as calcium-binding induces only strictly local structural changes. References

Protein domains