Two N-Terminal Domains of Kv4 K + Channels Regulate Binding to and Modulation by KChIP1

The family of calcium binding proteins called KChIPs associates with Kv4 family K + channels and modulates their biophysical properties. Here, using mutagenesis and X-ray crystallography, we explore the interaction between Kv4 subunits and KChIP1. Two regions in the Kv4.2 N terminus, residues 7–11 and 71–90, are necessary for KChIP1 modulation and interaction with Kv4.2. When inserted into the Kv1.2 N terminus, residues 71–90 of Kv4.2 are also sufficient to confer association with KChIP1. To provide a structural framework for these data, we solved the crystal structures of Kv4.3N and KChIP1 individually. Taken together with the mutagenesis data, the individual structures suggest that that the Kv4 N terminus is required for stable association with KChIP1, perhaps through a hydrophobic surface interaction, and that residues 71–90 in Kv4 subunits form a contact loop that mediates the specific association of KChIPs with Kv4 subunits.