title: Charybdotoxin binding in the I(Ks) pore demonstrates two MinK subunits in each channel complex.
abstract: I(Ks) voltage-gated K(+) channels contain four pore-forming KCNQ1 subunits and MinK accessory subunits in a number that has been controversial. Here, I(Ks) channels assembled naturally by monomer subunits are compared to those with linked subunits that force defined stoichiometries. Two strategies that exploit charybdotoxin (CTX)-sensitive subunit variants are applied. First, CTX on rate, off rate, and equilibrium affinity are found to be the same for channels of monomers and those with a fixed 2:4 MinK:KCNQ1 valence. Second, 3H-CTX and an antibody are used to directly quantify channels and MinK subunits, respectively, showing 1.97 +/- 0.07 MinK per I(Ks) channel. Additional MinK subunits do not enter channels of monomeric subunits or those with fixed 2:4 valence. We conclude that two MinK subunits are necessary, sufficient, and the norm in I(Ks) channels. This stoichiometry is expected for other K(+) channels that contain MinK or MinK-related peptides (MiRPs).
authors.affiliation: Department of Pediatrics, Boyer Center for Molecular Medicine, Yale University School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA.
authors.forename: Haijun
authors.initials: H
authors.lastname: Chen
authors.forename: Leo A
authors.initials: LA
authors.lastname: Kim
authors.forename: Sindhu
authors.initials: S
authors.lastname: Rajan
authors.forename: Shuhua
authors.initials: S
authors.lastname: Xu
authors.forename: Steve A N
authors.initials: SA
authors.lastname: Goldstein
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D018999:Charybdotoxin / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014981:Xenopus
chemical_list: D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; C059983:potassium channel protein I(sk); D018999:Charybdotoxin