Inhibition of human ether à go-go potassium channels by Ca(2+)/calmodulin

Intracellular CA(2+) inhibits voltage-gated potassium channels of the ether à go-go (EAG) family. To identify the underlying molecular mechanism, we expressed the human version hEAG1 in Xenopus oocytes. The channels lost CA(2+) sensitivity when measured in cell-free membrane patches. However, CA(2+) sensitivity could be restored by application of recombinant Calmodulin (CaM). In the presence of CaM, half inhibition of hEAG1 channels was obtained in 100 nM CA(2+). Overlay assays using labelled CaM and Glutathione S-transferase (GST) fusion fragments of hEAG1 demonstrated direct binding of CaM to a C-terminal domain (hEAG1 Amino acids 673-770). Point mutations within this section revealed a novel CaM-binding domain putatively forming an amphipathic helix with both sides being important for binding. The binding of CaM to hEAG1 is, in contrast to CA(2+)-activated potassium channels, CA(2+) dependent, with an apparent K(D) of 480 nM. Co-expression experiments of wild-type and mutant channels revealed that the binding of one CaM molecule per channel complex is sufficient for channel inhibition.