Calmodulin Mediates Calcium-dependent Activation of the Intermediate Conductance KCa Channel,IKCa1
| Autor: | K. George Chandy, Christopher M. Fanger, Naomi J. Logsdon, K. Kalman, Heiko Rauer, Sanjiv Ghanshani, Jianming Zhou, Jayashree Aiyar, Michael D. Cahalan, Kathy Beckingham |
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| Rok vydání: | 1999 |
| Předmět: |
Potassium Channels
Calmodulin Molecular Sequence Data Mutant Gating Biology Biochemistry SK channel Tumor Cells Cultured Animals Humans Amino Acid Sequence Molecular Biology Membrane potential chemistry.chemical_classification Sequence Homology Amino Acid Conductance Cell Biology Intermediate-Conductance Calcium-Activated Potassium Channels Precipitin Tests Rats Cell biology Amino acid chemistry Cytoplasm biology.protein Calcium Calcium Channels Ion Channel Gating Protein Binding |
| Zdroj: | Journal of Biological Chemistry. 274:5746-5754 |
| ISSN: | 0021-9258 |
| DOI: | 10.1074/jbc.274.9.5746 |
| Popis: | Small and intermediate conductance Ca2+-activated K+ channels play a crucial role in hyperpolarizing the membrane potential of excitable and nonexcitable cells. These channels are exquisitely sensitive to cytoplasmic Ca2+, yet their protein-coding regions do not contain consensus Ca2+-binding motifs. We investigated the involvement of an accessory protein in the Ca2+-dependent gating of hIKCa1, a human intermediate conductance channel expressed in peripheral tissues. Cal- modulin was found to interact strongly with the cytoplasmic carboxyl (C)-tail of hIKCa1 in a yeast two-hybrid system. Deletion analyses defined a requirement for the first 62 amino acids of the C-tail, and the binding of calmodulin to this region did not require Ca2+. The C-tail of hSKCa3, a human neuronal small conductance channel, also bound calmodulin, whereas that of a voltage-gated K+ channel, mKv1.3, did not. Calmodulin co-precipitated with the channel in cell lines transfected with hIKCa1, but not with mKv1. 3-transfected lines. A mutant calmodulin, defective in Ca2+ sensing but retaining binding to the channel, dramatically reduced current amplitudes when co-expressed with hIKCa1 in mammalian cells. Co-expression with varying amounts of wild-type and mutant calmodulin resulted in a dominant-negative suppression of current, consistent with four calmodulin molecules being associated with the channel. Taken together, our results suggest that Ca2+-calmodulin-induced conformational changes in all four subunits are necessary for the channel to open. |
| Databáze: | OpenAIRE |
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