title: Mutational and in silico analyses for antidepressant block of astroglial inward-rectifier Kir4.1 channel.
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 transmembrane domain 2 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.
authors.affiliation: Department of Pharmacology, Center for Advanced Medical Engineering and Informatics, Osaka University, Japan.
authors.forename: Kazuharu
authors.initials: K
authors.lastname: Furutani
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Ohno
authors.forename: Atsushi
authors.initials: A
authors.lastname: Inanobe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hibino
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kurachi
mesh_terms: D000818:Animals; D000928:Antidepressive Agents / Q000737:chemistry / Q000494:pharmacology*; D001253:Astrocytes / Q000378:metabolism*; D001665:Binding Sites; D002460:Cell Line; D005260:Female; D005473:Fluoxetine / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D006860:Hydrogen Bonding; D066298:In Vitro Techniques; D008024:Ligands; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009661:Nortriptyline / Q000737:chemistry / Q000494:pharmacology; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors* / Q000235:genetics; D011487:Protein Conformation; D021281:Quantitative Structure-Activity Relationship; D051381:Rats; D014982:Xenopus laevis; D000098854:Kcnj10 Channel
chemical_list: D000928:Antidepressive Agents; D000098854:Kcnj10 Channel; D008024:Ligands; D024661:Potassium Channels, Inwardly Rectifying; D005473:Fluoxetine; D009661:Nortriptyline