An Epithelial Ca2+-Sensor Protein is an Alternative to Calmodulin to Compose Functional 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-...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Cell Physiol Biochem Press GmbH & Co KG
2015-07-01
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| Series: | Cellular Physiology and Biochemistry |
| Subjects: | |
| Online Access: | http://www.karger.com/Article/FullText/430155 |
| Summary: | 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. |
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| ISSN: | 1015-8987 1421-9778 |