Calcium ions interact with residues contained within the loop region.
Each of the 12 residues in the loop region is important for calcium coordination. In most EF-hand proteins the residue at position 12 is a glutamate. The glutamate contributes both its side-chan oxygens for calcium coordination. Domain Binding and function The EF-hand motif contains approximately 40 residues and is involved in binding intracellular calcium. Binding of calcium to regulatory EF hand domain-containing proteins induces a conformational change, which is transmitted to their target proteins, often catalyzing enzymatic reactions.