Allosteric inhibitors targeting the calmodulin-PIP2 interface of SK4 K+ channels for atrial fibrillation treatment

Shira Burg, Shir Shapiro, Asher Peretz, Elvira Haimov, Boris Redko, Adva Yeheskel, Luba Simhaev, Hamutal Engel, Avi Raveh, Ariel Ben-Bassat, Michael Murninkas, Rotem Polak, Yoni Haitin, Yoram Etzion, Bernard Attali

Research output: Contribution to journalArticlepeer-review

Abstract

The Ca2+-activated SK4 K+ channel is gated by Ca2+-calmodulin (CaM) and is expressed in immune cells, brain, and heart. A cryoelectron microscopy (cryo-EM) structure of the human SK4 K+ channel recently revealed four CaM molecules per channel tetramer, where the apo CaM C-lobe and the holo CaM N-lobe interact with the proximal carboxyl terminus and the linker S4-S5, respectively, to gate the channel. Here, we show that phosphatidylinositol 4-5 bisphosphate (PIP2) potently activates SK4 channels by docking to the boundary of the CaM-binding domain. An allosteric blocker, BA6b9, was designed to act to the CaM-PIP2-binding domain, a previously untargeted region of SK4 channels, at the interface of the proximal carboxyl terminus and the linker S4-S5. Site-directed mutagenesis, molecular docking, and patch-clamp electrophysiology indicate that BA6b9 inhibits SK4 channels by interacting with two specific residues, Arg191 and His192 in the linker S4-S5, not conserved in SK1-SK3 subunits, thereby conferring selectivity and preventing the Ca2+-CaM N-lobe from properly interacting with the channel linker region. Immunohistochemistry of the SK4 channel protein in rat hearts showed a widespread expression in the sarcolemma of atrial myocytes, with a sarcomeric striated Z-band pattern, and a weaker occurrence in the ventricle but a marked incidence at the intercalated discs. BA6b9 significantly prolonged atrial and atrioventricular effective refractory periods in rat isolated hearts and reduced atrial fibrillation induction ex vivo. Our work suggests that inhibition of SK4 K+ channels by targeting drugs to the CaM-PIP2-binding domain provides a promising anti-arrhythmic therapy.

Original languageEnglish
Article numbere2202926119
Number of pages10
JournalProceedings of the National Academy of Sciences of the United States of America
Volume119
Issue number34
DOIs
StatePublished - 15 Aug 2022

Keywords

  • atrial fibrillation
  • calmodulin
  • KCa3.1
  • PIP2
  • potassium channel

ASJC Scopus subject areas

  • General

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