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J. Biol. Chem., Vol. 281, Issue 47, 35735-35741, November 24, 2006

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The Potassium Channel KAT1 Is Activated by Plant and Animal 14-3-3 Proteins^*

Barbara Sottocornola, Sabina Visconti, Sara Orsi, Sabrina Gazzarrini, Sonia Giacometti, Claudio Olivari, Lorenzo Camoni, Patrizia Aducci, Mauro Marra, Alessandra Abenavoli, Gerhard Thiel^¶, and Anna Moroni^||1

From the Dipartimento di Biologia and Istituto di Biofisica-Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, 20133 Milano, Italy, Dipartimento di Biologia, Università degli Studi di Roma "Tor Vergata," 00133 Roma, Italy, ^¶Institut für Botanik, Technische Universität Darmstadt, D-64287 Darmstadt, Germany, and ^||Istituto Nazionale Fisica della Materia-Unitàdi Milano Università, 20133 Milano, Italy

14-3-3 proteins modulate the plant inward rectifier K⁺ channel KAT1 heterologously expressed in Xenopus oocytes. Injection of recombinant plant 14-3-3 proteins into oocytes shifted the activation curve of KAT1 by +11 mV and increased the _on. KAT1 was also modulated by 14-3-3 proteins of Xenopus oocytes. Titration of the endogenous 14-3-3 proteins by injection of the peptide Raf 621p resulted in a strong decrease in KAT1 current (70% at –150 mV). The mutation K56E performed on plant protein 14-3-3 in a highly conserved recognition site prevented channel activation. Because the maximal conductance of KAT1 was unaffected by 14-3-3, we can exclude that they act by increasing the number of channels, thus ruling out any effect of these proteins on channel trafficking and/or insertion into the oocyte membrane. 14-3-3 proteins also increased KAT1 current in inside-out patches, suggesting a direct interaction with the channel. Direct interaction was confirmed by overlay experiments with radioactive 14-3-3 on oocyte membranes expressing KAT1.

Received for publication, April 7, 2006 , and in revised form, July 28, 2006.

^* This work was supported in part by Ministero dell'Istruzione, dell'Università e della Ricerca PRIN 2005 (to A. M.). 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.

¹ To whom correspondence should be addressed: Dipartimento di Biologia, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy. Tel.: 39-02503-14938; Fax: 39-02503-14932; E-mail: anna.moroni{at}unimi.it.

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