Mutant potassium channels with altered binding of charybdotoxin, a pore-blocking peptide inhibitor.
The inhibition by charybdotoxin of A-type potassium channels expressed in Xenopus oocytes was studied for several splicing variants of the Drosophila Shaker gene and for several site-directed mutants of this channel. Charybdotoxin blocking affinity is lowered by a factor of 3.5 upon replacing glutamate-422 with glutamine, and by a factor of about 12 upon substituting lysine in this position. Replacement of glutamate-422 by aspartate had no effect on toxin affinity. Thus, the glutamate residue at position 422 of this potassium channel is near or in the externally facing mouth of the potassium conduction pathway, and the positively charged toxin is electrostatically focused toward its blocking site by the negative potential set up by glutamate-422.
MacKinnon
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Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02254.
Miller
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D000818:Animals; D001665:Binding Sites; D018999:Charybdotoxin; D004252:DNA Mutational Analysis; D004331:Drosophila melanogaster; D007477:Ions; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D015221:Potassium Channels / Q000378:metabolism* / Q000648:ultrastructure; D012604:Scorpion Venoms / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014162:Transfection; D014982:Xenopus laevis
D007477:Ions; D008565:Membrane Proteins; D015221:Potassium Channels; D012604:Scorpion Venoms; D018999:Charybdotoxin