• First identified as a CaM binding motif in neuromodulin by DR Storm and colleagues (1988) the IQ motif was first characterized in myosins by Cheney and Mooseker (1992). Proteins that contain IQ motifs typically bind calmodulin in the absence of calcium, although there are some exceptions.
• IQ motifs frequently occur in tandem, such as in the myosins, although the binding stoichiometry for calmodulin to multiple IQ motifs is unclear.
• It has been suggested that 'complete' IQ motifs (containing the G and second basic residue) do not require calcium to bind calmodulin; binding of incomplete IQ motifs (lacking the second basic residue) is calcium dependent (Houdusse & Cohen (1995), Proc Natl Acad Sci 92:10644-7, Munshi et al (1996), Biochemistry 35:158823-9).

IQ Subclasses

• Characters within parentheses can substitute for each other.
• The first hydrophobic residue (preceding the Q) is predominantly I, V or L. The G after the first basic residue (almost always R) is not as conserved, nor is the hydrophobic residue two residues following the second basic residue.
• Crieteria for IQ-like motifs in this Database is loosened to accommodate a number of sequences that have been shown to bind calmodulin, including those that lack a hydrophobic residue preceding the Q. In some references, sequences lacking the Q but containing other conserved basic and hydrophobic residues have been described as IQ motifs, usually based on homology to another species or its appearance in tandem with other bona fide IQ motifs. These have been placed in the Undetermined class.

Data

Sequence Alignment, Data and Homologs