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Mapping the BKCa channel's "Ca2+ bowl": side-chains essential for Ca2+ sensing
Lin Bao1, Christina Kaldany, Ericka C Holmstrand
1Molecular Cardiology Research Institute, New England Medical Center, Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA.
The Journal of General Physiology
|April 28, 2004
Summary
Calcium (Ca2+) binding to the large conductance calcium-activated potassium (BKCa) channel
Area of Science:
- Molecular Biology
- Ion Channel Physiology
- Biochemistry
Background:
- The precise location of calcium (Ca2+) binding sites on the BKCa channel remains debated.
- The intracellular
- Ca2+ bowl
- region is a candidate for Ca2+ sensing, containing acidic residues crucial for channel function.
Purpose of the Study:
- To identify specific residues within the BKCa channel's Ca2+ bowl essential for Ca2+ sensing and binding.
- To investigate the relationship between Ca2+ sensing and Ca2+ binding affinities.
Main Methods:
- Site-directed mutagenesis to alter specific amino acid residues in the Ca2+ bowl.
- Ca2+ binding assays using a fusion protein of the BKCa channel's intracellular domain.
Main Results:
- Aspartic acid residues D898 and D900 in the Ca2+ bowl are critical for Ca2+ sensing.
- These residues are also essential for Ca2+ binding to the intracellular domain.
- A weaker correlation than expected was observed between mutations affecting Ca2+ sensing and Ca2+ binding.
Conclusions:
- Ca2+ likely binds to the intracellular domain of the BKCa channel, specifically involving the D898 and D900 residues in the Ca2+ bowl.
- The Ca2+ bowl contains a key motif for Ca2+ sensing.
- Potential nonnative conformations of the Ca2+ bowl in certain assays may explain discrepancies between binding and sensing.