The IQ calmodulin-binding motif is an

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...

sequence motif containing the following sequence: * ILVxxx Kxxx Kx ILVWY The term "IQ" refers to the first two amino acids of the motif: isoleucine (commonly) and

glutamine Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...

(invariably).

Function

Calmodulin (CaM) is recognized as a major

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...

(Ca²⁺) sensor and orchestrator of regulatory events through its interaction with a diverse group of cellular proteins. Three classes of recognition motifs exist for many of the known CaM binding proteins; the IQ motif as a consensus for Ca²⁺-independent binding and two related motifs for Ca²⁺-dependent binding, termed 1-14 and 1-5-10 based on the position of conserved

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, t ...

residues.

Example

The regulatory domain of scallop myosin is a three-chain protein complex that switches on this motor in response to Ca²⁺ binding. Side-chain interactions link the two light chains in tandem to adjacent segments of the heavy chain bearing the IQ-sequence motif. The Ca²⁺-binding site is a novel

EF hand The EF hand is a helix–loop–helix structural domain or ''motif'' found in a large family of calcium-binding proteins. The EF-hand motif contains a helix–loop–helix topology, much like the spread thumb and forefinger of the human hand, i ...

motif on the essential light chain and is stabilized by linkages involving the heavy chain and both light chains, accounting for the requirement of all three chains for Ca²⁺binding and regulation in the intact myosin molecule.

References

{{InterPro content, IPR000048 Protein domains