Site-specific mutations in a minimal voltage-dependent K+ channel alter ion selectivity and open-channel block.
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.
Goldstein
S A
SA
Howard Hughes Medical Institute, Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254-9110.
Miller
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C
D000595:Amino Acid Sequence; D000818:Animals; D004252:DNA Mutational Analysis; D005796:Genes; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000737:chemistry / Q000502:physiology*; D014982:Xenopus laevis
D015221:Potassium Channels; D011188:Potassium