MECHANISMS OF SIGNAL TRANSDUCTION
Identification of Common Binding Sites for Calmodulin and Inositol 1,4,5-Trisphosphate Receptors on the Carboxyl Termini of Trp Channels*

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Homologues of Drosophila Trp (transient receptor potential) form plasma membrane channels that mediate Ca2+ entry following the activation of phospholipase C by cell surface receptors. Among the seven Trp homologous found in mammals, Trp3 has been shown to interact with and respond to IP3 receptors (IP3Rs) for activation. Here we show that Trp4 and other Trp proteins also interact with IP3Rs. The IP3R-binding domain also interacts with calmodulin (CaM) in a Ca2+-dependent manner with affinities ranging from 10 nm for Trp2 to 290 nm for Trp6. In addition, other binding sites for CaM and IP3Rs are present in the α but not the μ isoform of Trp4. In the presence of Ca2+, the Trp-IP3R interaction is inhibited by CaM. However, a synthetic peptide representing a Trp-binding domain of IP3Rs inhibited the binding of CaM to Trp3, -6, and -7 more effectively than that to Trp1, -2, -4, and -5. In inside-out membrane patches, Trp4 is activated strongly by calmidazolium, an antagonist of CaM, and a high (50 μm) but not a low (5 μm) concentration of the Trp-binding peptide of the IP3R. Our data support the view that both CaM and IP3Rs play important roles in controlling the gating of Trp-based channels. However, the sensitivity and responses to CaM and IP3Rs differ for each Trp.

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Published, JBC Papers in Press, April 4, 2001, DOI 10.1074/jbc.M102316200

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The work was supported in part by National Institutes of Health Grants GM54235 (to M. X. Z.) and HL45198 (to L. B.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.