IQ calmodulin-binding motif

The IQ calmodulin-binding motif is an amino acid sequence motif containing the following sequence:

• [FILV]Qxxx[RK]Gxxx[RK]xx[FILVWY]

IQ calmodulin-binding motif
Structure of the regulatory domain of scallop myosin at 2 A resolution.[1]
Identifiers
Symbol	IQ
Pfam	PF00612
InterPro	IPR000048
SMART	SM00015
PROSITE	PS50096
SCOP2	1wdc / SCOPe / SUPFAM
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary PDB 1b7t​, 1br1​, 1br2​, 1br4​, 1d0x​, 1d0y​, 1d0z​, 1d1a​,1d1b​,1d1c​, 1dfk​, 1dfl​, 1fmv​, 1fmw​, 1jwy​, 1jx2​, 1kk7​, 1kk8​,1kqm​, 1kwo​, 1l2o​, 1lkx​, 1lvk​, 1mma​, 1mmd​, 1mmg​, 1mmn​,1mnd​, 1mne​, 1oe9​, 1qvi​, 1s5g​, 1scm​, 1sr6​, 1vom​, 1w7i​,1w7j​, 1wdc​, 2mys​

The term "IQ" refers to the first two amino acids of the motif: isoleucine (commonly) and glutamine (invariably).

Function

Calmodulin (CaM) is recognized as a major calcium (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 residues.^[2]

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 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.^[3]