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60  structures 1437  species 0  interactions 82891  sequences 2045  architectures

Family: IQ (PF00612)

Summary: IQ calmodulin-binding motif

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This is the Wikipedia entry entitled "IQ calmodulin-binding motif". More...

IQ calmodulin-binding motif Edit Wikipedia article

IQ calmodulin-binding motif
PDB 1wdc EBI.jpg
Structure of the regulatory domain of scallop myosin at 2 A resolution.[1]

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

  • [FILV]Qxxx[RK]Gxxx[RK]xx[FILVWY]

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


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]


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]


  1. ^ Houdusse A, Cohen C (January 1996). "Structure of the regulatory domain of scallop myosin at 2 A resolution: implications for regulation". Structure. 4 (1): 21–32. doi:10.1016/S0969-2126(96)00006-8. PMID 8805510.
  2. ^ Rhoads AR, Friedberg F (April 1997). "Sequence motifs for calmodulin recognition". FASEB J. 11 (5): 331–40. doi:10.1096/fasebj.11.5.9141499. PMID 9141499.
  3. ^ Xie X, Harrison DH, Schlichting I, Sweet RM, Kalabokis VN, Szent-Györgyi AG, Cohen C (March 1994). "Structure of the regulatory domain of scallop myosin at 2.8 A resolution". Nature. 368 (6469): 306–12. doi:10.1038/368306a0. PMID 8127365.
This article incorporates text from the public domain Pfam and InterPro: IPR000048

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Calmodulin-binding motif.

Literature references

  1. Xie X, Harrison DH, Schlichting I, Sweet RM, Kalabokis VN, Szent-Gyorgyi AG, Cohen C; , Nature 1994;368:306-312.: Structure of the regulatory domain of scallop myosin at 2.8 A resolution. PUBMED:8127365 EPMC:8127365

  2. Rhoads AR, Friedberg F; , FASEB J 1997;11:331-340.: Sequence motifs for calmodulin recognition. PUBMED:9141499 EPMC:9141499

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR000048

The IQ motif is an extremely basic unit of about 23 amino acids, whose conserved core usually fits the consensus A-x(3)-I-Q-x(2)-F-R-x(4)-K-K. The IQ motif, which can be present in one or more copies, serves as a binding site for different EF-hand proteins including the essential and regulatory myosin light chains, calmodulin (CaM), and CaM-like proteins [ PUBMED:1558751 , PUBMED:9141499 ].Many IQ motifs are protein kinase C (PKC) phosphorylation sites [ PUBMED:1824695 , PUBMED:8424932 ].

Resolution of the 3D structure of scallop myosin has shown that the IQ motif forms a basic amphipathic helix [ PUBMED:8127365 ].

Some proteins known to contain an IQ motif are listed below:

  • A number of conventional and unconventional myosins.
  • Neuromodulin (GAP-43). This protein is associated with nerve growth. It is a major component of the motile "growth cones" that form the tips of elongating axons.
  • Neurogranin (NG/p17). Acts as a "third messenger" substrate of protein kinase C-mediated molecular cascades during synaptic development and remodeling.
  • Sperm surface protein Sp17.
  • Ras GTPase-activating-like protein IQGAP1. IQGAP1 contains 4 IQ motifs.

This entry covers the entire IQ motif.

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Domain organisation

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We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database (reference proteomes) using the family HMM. We also generate alignments using four representative proteomes (RP) sets and the UniProtKB sequence database. More...

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Curation and family details

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Seed source: SMART
Previous IDs: none
Type: Motif
Sequence Ontology: SO:0001067
Author: Ponting CP , Schultz J, Bork P
Number in seed: 245
Number in full: 82891
Average length of the domain: 20.60 aa
Average identity of full alignment: 33 %
Average coverage of the sequence by the domain: 4.54 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.3 11.1
Trusted cut-off 20.3 11.1
Noise cut-off 20.2 11.0
Model length: 21
Family (HMM) version: 29
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Species distribution

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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the IQ domain has been found. There are 60 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.

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