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Site-specific mutations in a minimal voltage-dependent K+ channel alter ion selectivity and open-channel block
1Howard Hughes Medical Institute, Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254-9110.
Abstract:
MinK is a small membrane protein of 130 amino acids with a single potential membrane-spanning alpha-helical domain. Its expression in Xenopus oocytes induces voltage-dependent, K(+)-selective channels. Using site-directed mutagenesis of a synthetic gene, we have identified residues in the hydrophobic region of minK that influence both ion selectivity and open-channel block. Single amino acid changes increase the channel's relative permeability for NH4+ and Cs+ without affecting its ability to exclude Na+ and Li+. Blockade by two common K+ channel pore blockers, tetraethylammonium and Cs+, was also modified. These results suggest that an ion selectivity region and binding sites for the pore blockers within the conduction pathway have been modified. We conclude that the gene encoding minK is a structural gene for a K+ channel protein.
Insights
Mutations in the minK gene alter potassium channel properties. Specific amino acid changes modify ion selectivity and block by pore blockers, confirming minK
Area of Science:
- Molecular biology
- Biophysics
- Ion channel function
Background:
- MinK is a small membrane protein that forms potassium channels.
- These channels are voltage-dependent and K(+)-selective.
- Understanding MinK's structure-function relationship is crucial for ion channel research.
Purpose of the Study:
- To investigate the role of specific amino acid residues in the minK protein.
- To determine how mutations affect ion selectivity and channel block.
- To elucidate the structural basis of K+ channel function.
Main Methods:
- Site-directed mutagenesis of a synthetic minK gene.
- Expression of mutated minK in Xenopus oocytes.
- Electrophysiological analysis of channel properties.
Main Results:
- Single amino acid substitutions altered ion permeability, increasing relative permeability for NH4+ and Cs+.
- Mutations did not affect the exclusion of Na+ and Li+.
- Changes in MinK modified the blockade by tetraethylammonium and Cs+.
Conclusions:
- The hydrophobic region of minK contains residues critical for ion selectivity and pore blocker binding.
- MinK protein directly contributes to the structure of the K+ channel pore.
- The gene encoding minK is a structural gene for a K+ channel protein.