BACKGROUND/AIMS: 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. CONCLUSION: 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.
BACKGROUND/AIMS: 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. CONCLUSION: 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: Marjolein J Peters; Paul S de Vries; Mohsen Ghanbari; Cindy G Boer; Jeroen G J van Rooij; Yu-Chi Lee; Vinod Kumar; André G Uitterlinden; M Arfan Ikram; Cisca Wijmenga; Jose M Ordovas; Caren E Smith; Joyce B J van Meurs; Stefan J Erkeland; Oscar H Franco; Abbas Dehghan Journal: J Hum Genet Date: 2018-01-30 Impact factor: 3.172