Cloning and expression of a novel K+ channel regulatory protein, KChAP

Voltage-gated K+ (Kv) channels are important in the physiology of both excitable and nonexcitable cells. The diversity in Ky currents is reflected in multiple Kv channel genes whose products may assemble as multisubunit heteromeric complexes. Given the fundamental importance and diversity of Ky channels, surprisingly little is known regarding the cellular mechanisms regulating their synthesis, assembly, and metabolism. To begin to dissect these processes, we have used the yeast two-hybrid system to identify cytoplasmic regulatory molecules that interact with Ky channel proteins. Here we report the cloning of a novel gene encoding a Ky channel binding protein (KChAP, for K+ channel-associated protein), which modulates the expression of Kv2 channels in heterologous expression system assays, KChAP interacts with the N termini of Kv alpha 2 subunits, as well as the N termini of Kv alpha 1 and the C termini of Kv beta subunits, Kv2.1 and KChAP were coimmunoprecipitated from in vitro translation reactions supporting a direct interaction between the two proteins. The amplitudes of Kv2.1 and Kv2.2 currents are enhanced dramatically in Xenopus oocytes coexpressing RChAP, but channel kinetics and gating are unaffected. Although KChAP binds to Kv1.5, it has no effect on Kv1.5 currents. We suggest that RChAP may act as a novel type of chaperone protein to facilitate the cell surface expression of Kv2 channels.