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A mutant KcsA K(+) channel with altered conduction properties and selectivity filter ion distribution
Ming Zhou1, Roderick MacKinnon
1Howard Hughes Medical Institute and Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, New York, NY 10021, USA.
Journal of Molecular Biology
|April 22, 2004
Summary
Mutating threonine to cysteine in potassium channels alters ion distribution and reduces conduction rates. This affects potassium ion (K+) but not rubidium ion (Rb+) transport, suggesting a specific conduction mechanism.
Area of Science:
- Molecular Biophysics
- Ion Channel Physiology
Background:
- Potassium (K+) channel selectivity filters contain four ion-binding sites crucial for ion transport.
- Site 4 is unique, incorporating both main-chain carbonyl and threonine side-chain hydroxyl oxygens.
Purpose of the Study:
- To investigate the functional impact of mutating the threonine residue at site 4 to cysteine.
- To elucidate the role of threonine in ion distribution and K+ conduction within the selectivity filter.
Main Methods:
- Site-directed mutagenesis of the threonine residue to cysteine in the K+ channel.
- Characterization of ion distribution and conduction properties using electrophysiological techniques.
Main Results:
- The threonine-to-cysteine mutation altered K+ occupancy at binding sites 2 and 4.
- A reduced maximum rate of K+ conduction was observed at high K+ concentrations.
- Rubidium ion (Rb+) conduction remained unaffected by the mutation.
Conclusions:
- The threonine residue at site 4 is critical for optimal K+ ion distribution and conduction.
- Results support a conduction model involving K+ ion pairs switching between 1,3 and 2,4 configurations.