Structure-function studies of loss-of-function KCa2.2 mutant channels.

Abstract

Small-conductance Ca2+-activated potassium subtype 2 (KCa2.2, also called SK2) channels are operated exclusively by a Ca2+-calmodulin gating mechanism. Wild-type KCa2.2 channels have an apparent sensitivity to Ca2+ of ∼0.3 μM. Heterozygous genetic mutations of KCa2.2 channels have been associated with autosomal dominant neurodevelopmental disorders including cerebellar ataxia and tremor in humans and rodents. These pathogenic KCa2.2 mutations cause complete loss of channel activity when expressed by themselves in HEK293 cells. When co-expressed with the KCa2.2_WT channel, mutations of pore-lining residues dominant negatively suppressed and completely abolished channel activity. Two proline substitutions in the transmembrane S2 domain and HA/HB helices also completely abolished the current of the co-expressed KCa2.2_WT channels. Co-expression of the KCa2.2_I289N and the KCa2.2_WT channels reduced the apparent Ca2+ sensitivity compared with the WT channel, which was rescued by a KCa2.2 positive modulator.