FIGURE 4.

Identification of a desensitization motif in the H1 domains of KCTD12 and -12b. A, sequence alignment of residues Asn²⁷⁷-Ser²⁸⁹ in the KCTD12 H1 domain with the corresponding sequences in KCTD8, -16, and -12b. Stars and dots indicate identical and similar amino acids, respectively. B and C, representative traces of GABA_B-activated Kir3 currents recorded at −50 mV from CHO cells expressing GABA_B(1b,2), Kir3 channels and KCTD proteins. Substitution of Tyr²⁷⁸ by Phe in KCTD8 lacking its H2 domain (8ΔH2 and 8ΔH2F; B) induces Kir3-current desensitization. Substitution of Lys²³¹, His²³², and Arg²³⁵ by NFQ in KCTD16 lacking its H2 domain (16ΔH2NFQ) induces current desensitization, while substitution of His²³² by Phe alone (16ΔH2F) is insufficient for this (C). D, bar graph summarizing the desensitization of Kir3 currents in the presence of KCTD proteins. Data are expressed as mean ± S.D.; *, p < 0.05; **, p < 0.01 compared with cells without KCTD proteins (Dunnett's multiple comparison test). E, substitution of Asn²⁷⁷, Phe²⁷⁸, and Gln²⁸¹ by KHR in KCTD12 (12KHR) eliminates Kir3 current desensitization, while substitution of Phe²⁷⁸ by H alone (12H) is insufficient for this. F, bar graph summarizing the desensitization of Kir3 currents in the presence of KCTD proteins. Data are expressed as mean ± S.D.; ***, p < 0.001 compared with cells transfected with KCTD12 (Dunnett's multiple comparison test).