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 ref lected in multiple Kv channel genes whose products may assemble as mul tisubunit heteromeric complexes. Given the fundamental importance and diversity of Ky channels, surprisingly little is known regarding the c ellular mechanisms regulating their synthesis, assembly, and metabolis m. To begin to dissect these processes, we have used the yeast two-hyb rid system to identify cytoplasmic regulatory molecules that interact with Ky channel proteins. Here we report the cloning of a novel gene e ncoding a Ky channel binding protein (KChAP, for K+ channel-associated protein), which modulates the expression of Kv2 channels in heterolog ous 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 te rmini of Kv beta subunits, Kv2.1 and KChAP were coimmunoprecipitated f rom in vitro translation reactions supporting a direct interaction bet ween the two proteins. The amplitudes of Kv2.1 and Kv2.2 currents are enhanced dramatically in Xenopus oocytes coexpressing RChAP, but chann el 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 expres sion of Kv2 channels.