Calcium negatively modulates calmodulin interaction with IQGAP1

Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, United States
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 06/2004; 317(3):787-95. DOI: 10.1016/j.bbrc.2004.03.119
Source: PubMed


IQGAP1 regulates cytoskeletal dynamics through interactions with the Rho family GTPases Rac1 and Cdc42, F-actin, and beta-catenin. Calmodulin interaction with IQ motifs of IQGAP1 negatively influences these IQGAP1 interactions. Although, calmodulin interacts with IQGAP1 in the absence of Ca(2+) and was suggested to exhibit reduced binding when Ca(2+) bound, recent reports show substantially greater binding when Ca(2+) is present. Binding evaluations have primarily relied on IQGAP1 interaction with calmodulin conjugated to Sepharose 4B. In this study we evaluated the Ca(2+)-dependence of calmodulin interaction with native IQGAP1 using a series of independent biochemical approaches. We found the apparent binding of calmodulin to IQGAP1 was Ca(2+)-independent, being between 5- and 20-fold greater in the absence than in the presence of Ca(2+). In addition, calmodulin interaction with IQGAP1 was negatively regulated by buffer [Ca(2+)] (IC(50)=3.4x10(-7)M). Regulation was specific to Ca(2+), as Ba(2+) was approximately 400-fold less effective than Ca(2+) at modulating the interaction. Moreover, testing of calmodulin mutants demonstrated that apocalmodulin tightly binds IQGAP1 and that the N- and C-terminal pair of EF hands are important for Ca(2+) sensitivity. These data indicate that calmodulin may disassemble from IQGAP1 to facilitate IQGAP1 interaction with effectors of cytoskeletal reorganization during conditions of cell activation that promote increased cytosolic [Ca(2+)].

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    • "IQGAP1 contains multiple protein-interacting domains: the CH (calponin homology) domain binds to F-actin, the WW domain binds to ERK2, the IQ repeat motifs bind to calmodulin and myosin light chain, and the Ras GAP-like domain binds to Cdc42 and Rac1 [25]–[32]. IQGAP1 is also known to bind to E-cadherin and ß-catenin, and is involved in cytoskeltal reorganization and cell adhesion [33], [34]. On the other hand, IQGAP1 stimulates ß-catenin-mediated transcriptional activation34. "
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