EF-Hand Domain
EF-Hand Domain

No ImageThe basic EF-hand consists of two perpendicular 10 to 12 residue alpha helices with a 12-residue loop region between, forming a single calcium-binding site (helix-loop-helix). 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 EF-hand motifs, residues 1, 3, 5, 7, 9, and 12 of the conserved loop region provide oxygen ligands to the calcium ion necessary for its binding. In most EF-hand proteins the residue at position 12 is a glutamate. The glutamate contributes both its side-chan oxygens for calcium coordination. Variations in calcium binding affinity for different EF-hand proteins is due to the amino-acid composition in the 1, 3, 5, 7, and 9 positions.

Structure Reference:

Domain binding and function:
The EF-hand motif contains approximately 40 residues and is involved in binding intracellular calcium. EF-hand domains are often found in single or multiple pairs, giving rise to various structural/functional variations in proteins containing EF-hand motifs. Proteins containing EF-hands can be grouped into two functional categories - regulatory or structural. 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. In contrast, binding of calcium to structural EF-hand domain-containing proteins does not induce a significant conformational change. Structural EF-hand domains seem to play a role in buffering intracellular calcium levels.
Examples of Proteins: 
EF-h domain protein
Binding partner function
Calmodulin Ca2+ Regulatory proteins
S-100 Ca2+ Regulatory proteins
recoverin Ca2+ Regulatory proteins
calbindin Ca2+ Structural proteins
parvalbumin Ca2+ Structural proteins

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