Calmodulin bridging of IQ motifs in myosin-V

Ca2+-saturated calmodulin binds to double-length IQ lever-arm sequences from murine myosin-V, forming a 1:1 "bridging" complex with very high affinity, (K-d < 10 pM for double motifs, IQ34, IQ45 and IQ56). Such a 1:1 complex involves interaction of one calmodulin (CaM) molecule with two adjacent IQ-motifs, providing a molecular mechanism for the observed Ca2+-dependent CaM dissociation from the IQ-region. Structural considerations suggest that formation of the 1:1 complex requires a severe distortion of the lever-arm, potentially regulating functional motility. This would be consistent with a recent report of diverse, irregular shapes of the lever arm of myosin-V induced by the presence of Ca2+. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.