Abstract
Drug interaction with target proteins including ion channels is essential for pharmacological control of various cellular functions, but the majority of its molecular mechanisms is still elusive. We recently found that a series of antidepressants preferentially block astroglial K+-buffering inwardly rectifying potassium channel (Kir) 4.1 channels over Kir1.1 channels. Here, using electrophysiological analyses of drug action on mutated Kir4.1 channel as well as computational analyses of three-dimensional (3D) arrangements of the ligands (i.e., bidirectional analyses), we examined the underlying mechanism for the antidepressant-Kir4.1 channel interaction. First, the effects of the selective serotonin reuptake inhibitor fluoxetine and the tricyclic antidepressant nortriptyline on chimeric and site-directed mutants of Kir4.1 expressed in Xenopus laevis oocytes were examined using the two-electrode voltage-clamp technique. Two amino acids, Thr128 and Glu158, on pore and transmembrane domain 2 helices were critical for the drug inhibition of the current. The closed and open conformation models of the Kir4.1 pore suggested that both residues faced the central cavity, and they were positioned within a geometrical range capable of interacting with the drugs. Second, to represent molecular properties of active ligands in geometric terms, a 3D quantitative structure-activity relationship model of antidepressants was generated, which suggested that they share common features bearing a hydrogen bond acceptor and a positively charged moiety. 3D structures and physicochemical features of receptor and ligand were fitted together. Our results strongly suggest that antidepressants interact with Kir4.1 channel pore residues by hydrogen bond and ionic interactions, which account for their preferential inhibitory action on Kir4.1 current. This study may represent a possible general approach for the understanding of the mechanism of ligand-protein interactions.
Footnotes
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This work was supported by the Ministry of Education, Culture, Sports, Science, and Technology of Japan [Grants for the Leading Project for Biosimulation “Development of models for disease and drug action,” the global COE program in silico medicine at Osaka University, Scientific Research (A) 20249012, Young Scientists (B) 20790207, and Scientific Research on Priority Areas 17081012]; and the Ichiro Kanehara Foundation.
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K.F. and Y.O. contributed equally to this work.
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ABBREVIATIONS: Kir, inwardly rectifying potassium; 3D, three-dimensional; EK, K+ equilibrium potential; QSAR, quantitative structure-activity relationship; TM, transmembrane; WT, wild type.
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↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
- Received October 22, 2008.
- Accepted March 3, 2009.
- The American Society for Pharmacology and Experimental Therapeutics
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