The EF hand is a helix-turn-helix structural motif in proteins. It consists of two alpha helices positioned roughly perpendicular to one another and linked by a short loop region (usually about 12 amino acids) that often binds calcium ions. The motif takes its name from traditional nomenclature used in describing the protein parvalbumin, which contains three such motifs and is probably involved in muscle relaxation via its calcium-binding activity. EF hands also appear in each structural domain of the signaling protein calmodulin and in the muscle protein troponin-C. The λ repressor of bacteriophage lambda employs a helix-turn-helix to bind DNA. In proteins, the helix-turn-helix (HTH) is a major structural motif capable of binding DNA. It is composed of two α helices joined by a short strand of amino acids and is found in many... It has been suggested that Supersecondary structure be merged into this article or section. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A diagram of the alpha helix structure of amino acids In proteins, the α helix is a major structural motif in secondary structure. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse, referring to muscles like the biceps which pop up as though a mouse were scurrying about under the skin [1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ... Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. ... Calmodulin 3D structure Calmodulin (CaM) is a Ca2+-binding protein that is a key component of the Ca2+ second-messenger system and is involved in controlling many of the biochemical processes of cells. ...

Sequence specificity

The calcium ion is bound by both protein backbone atoms and by amino acid side chains, specifically those of aspartate and glutamate. The EF hand motif was among the first structural motifs whose sequence requirements were analyzed in detail. Five of the loop residues bind calcium and thus have a strong preference for oxygen-containing side chains, especially aspartate and glutamate. The sixth residue in the loop is necessarily glycine due to the conformational requirements of the backbone. The remaining residues are typically hydrophobic and form a hydrophobic core that binds the stabilizes the two helices. A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). ... The term Side chain can have different meanings depending on the context: In chemistry and biochemistry a side chain is a part of a molecule attached to a core structure. ... Aspartic acid, also known as aspartate, the name of its anion, is one of the 20 natural proteinogenic amino acids which are the building blocks of proteins. ... Glutamate is the anion of glutamic acid. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ... Glycine (Gly, G) is a nonpolar amino acid. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... The hydrophobic effect is the property that nonpolar molecules like to self-associate in the presence of aqueous solution. ...

Another distinct calcium-binding motif composed of alpha helices is the dockerin domain.

External links

• SCOP EF-hand fold

References

• Branden C, Tooze J. (1999). Introduction to Protein Structure 2nd ed. Garland Publishing: New York, NY.