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Ion Channels and Excitable Membranes

開催日 2014/9/12
時間 14:00 - 15:00
会場 Poster / Exhibition(Event Hall B)

Structural basis for the membrane association of ankyrinG: the ion channel anchoring protein

  • P2-014
  • 藤原 祐一郎 / Yuichiro Fujiwara:1 城田 松之 / Matsuyuki Shirota:2,4,5 小林 恵 / Megumi Kobayashi:1 竹下 浩平 / Kohei Takeshita:3 中川 敦史 / Atsushi Nakagawa:3 木下 賢吾 / Kengo Kinoshita:2,5 岡村 康司 / Yasushi Okamura:1 
  • 1:大阪大学 医学系研究科 統合生理学 / Integrative Physiology, Grad Sch of Med., Osaka University 2:東北大学 情報科学研究科 生命情報システム科学 / Systems Bioinformatics, Grad Sch of Inf. Sci., Tohoku University 3:大阪大学 蛋白質研究所 超分子構造解析学 / Supramolecular Crystallography, Protein Inst., Osaka University 4:東北大学 医学系研究科 附属創生応用医学研究センター / United Centers for Advanced Research and Translational Medicine, Grad Sch of Med., Tohoku University 5:東北大学 東北メディカルメガバンク機構 / Tohoku Medical Megabank Organization, Tohoku University  

AnkyrinG configures the membrane-excitation platform by clustering various ion channels such as voltage-gated Na+ channels, voltage-gated K+ channels, Na+-K+ ATPase and CNG channels at the initial segment and the nodes of Ranvier of axons, at the intercalated disk of cardiomyocytes or at the outer segment of retinal rod cells. Disorder of the clustering induces channelopathy, such as the Brugada syndrome and the periodic paralysis, and ankyrinG itself involved in the bipolar disorder. Elucidation of the molecular mechanism for clustering the channels on the membrane, thus, will bring significant merits, but so far no structural analysis of ankyrinG has been performed. AnkyrinG consists of 24 ankyrin repeats, and the channels are known to bind somewhere in the repeats; and ankyrinG itself associates to the plasma membrane via the s-palmitoylation of Cys in the 1st repeat. We expressed and purified a large amount of rat ankyrinG protein in E.coil. We succeeded in determining the high resolution (1.6 Å) crystal structure of the initial 5 ankyrin repeats, which uncovers the atomic structure of the interaction interface around the Cys to membrane lipids. The structure contains Ca2+ near the Cys, and two different structures concerning the 1st ankyrin repeat were obtained redox-dependently; which might be involved in some physiological modifications in activating neurons. Molecular dynamics analysis indicated that the ankyrin protein without s-palmitoylation interacted with the lipid bilayer but did not determine a unique binding interface. Surface plasmon resonance analysis also showed an extremely low binding affinity of the unpalmitoylated ankyrin to the lipid-bilayer. Thus, stable binding of ankyrinG to the plasma membrane would be determined by the rigid structure involving the s-palmitoylation.

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