title: An Epithelial Ca2+-Sensor Protein is an Alternative to Calmodulin to Compose Functional KCNQ1 Channels.
abstract: OBJECTIVE
  KCNQ channels transport K+ ions and participate in various cellular functions. The channels directly assemble with auxiliary proteins such as a ubiquitous Ca2+- sensor protein, calmodulin (CaM), to configure the physiological properties in a tissue-specific manner. Although many CaM-like Ca2+-sensor proteins have been identified in eukaryotes, how KCNQ channels selectively interact with CaM and how the homologues modulate the functionality of the channels remain unclear.
  
  
  METHODS
  We developed protocols to evaluate the interaction between the green fluorescent protein-tagged C-terminus of KCNQ1 (KCNQ1cL) and Ca2+-sensors by detecting its fluorescence in size exclusion chromatography and electrophoresed gels. The effects of Ca2+-sensor proteins on KCNQ1 activity was measured by two electrode voltage clamp technique of Xenopus oocytes.
  
  
  RESULTS
  When co-expressed CaM and KCNQ1cL, they assemble in a 4:4 stoichiometry, forming a hetero-octamer. Among nine CaM homologues tested, Calml3 was found to form a hetero-octamer with KCNQ1cL and to associate with the full-length KCNQ1 in a competitive manner with CaM. When co-expressed in oocytes, Calml3 rendered KCNQ1 channels resistant to the voltage-dependent depletion of phosphatidylinositol 4,5-bisphosphate by voltage-sensitive phosphatase.
  
  
  CONCLUSIONS
  Since Calml3 is closely related to CaM and is prominently expressed in epithelial cells, Calml3 may be a constituent of epithelial KCNQ1 channels and underscores the molecular diversity of endogenous KCNQ1 channels.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Inanobe
authors.forename: Chizuru
authors.initials: C
authors.lastname: Tsuzuki
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kurachi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002147:Calmodulin / Q000502:physiology*; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D049452:Green Fluorescent Proteins / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D014982:Xenopus laevis
chemical_list: D002147:Calmodulin; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D049452:Green Fluorescent Proteins