Desensitized mutant channels. cGMP-activated currents in the presence of 1 mM cGMP at +60 mV in the WT (A) and mutant channels E363A (B), T355A (C), L356A (D), and F380A (E). cGMP was added as indicated by the solid horizontal black bars. (F) Sequence alignment between CNGA1, Shaker, K_v1.2, K_v2.1, KcsA, and NaK channels. The TVGYG signature of K⁺ channels is highlighted in yellow. Amino acids that become more accessible upon desensitization or C-type inactivation are highlighted in green. The sequence alignment was performed by using Clustal W (Thompson et al., 1994).