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J. Biol. Chem., Vol. 278, Issue 50, 49667-49670, December 12, 2003

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ACCELERATED PUBLICATIONS

A New Role for IQ Motif Proteins in Regulating Calmodulin Function^*

John A. Putkey, Quinn Kleerekoper, Tara R. Gaertner¶, and M. Neal Waxham¶

From the Departments of Biochemistry and Molecular Biology, and ^¶Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030

IQ motifs are found in diverse families of calmodulin (CaM)-binding proteins. Some of these, like PEP-19 and RC3, are highly abundant in neuronal tissues, but being devoid of catalytic activity, their biological roles are not understood. We hypothesized that these IQ motif proteins might have unique effects on the Ca²⁺ binding properties of CaM, since they bind to CaM in the presence or absence of Ca²⁺. Here we show that PEP-19 accelerates by 40 to 50-fold both the slow association and dissociation of Ca²⁺ from the C-domain of free CaM, and we identify the sites of interaction between CaM and PEP-19 using NMR. Importantly, we demonstrate that PEP-19 can also increase the rate of dissociation of Ca²⁺ from CaM when bound to intact CaM-dependent protein kinase II. Thus, PEP-19, and presumably similar members of the IQ family of proteins, has the potential to alter the Ca²⁺-binding dynamics of free CaM and CaM that is bound to other target proteins. Since Ca²⁺ binding to the C-domain of CaM is the rate-limiting step for activation of CaM-dependent enzymes, the data reveal a new concept of importance in understanding the temporal dynamics of Ca²⁺-dependent cell signaling.

Received for publication, August 21, 2003 , and in revised form, September 22, 2003.

^* This work was supported in part by National Institutes of Health Grants HL45724 and NS26086 and Robert A. Welch Foundation Grant AU1144. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains part of the "Experimental Procedures."

To whom correspondence should be addressed: Depts. of Biochemistry and Molecular Biology, University of Texas Medical School, 6431 Fannin, Houston, TX 77030. Tel.: 713-500-6061; Fax: 713-500-0652; E-mail: John.Putkey{at}uth.tmc.edu.

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