Purification of an EH domain-binding protein from rat brain that modulates the gating of the rat ether-à-go-go channel.

Mutations in the gene encoding ether-à-go-go (EAG) potassium channel impair the function of several classes of potassium currents, synaptic transmission, and learning in Drosophila. Absence of EAG abolishes the modulation of a broad group of potassium currents. EAG has been proposed to be a regulatory subunit of different potassium channels. To further explore this regulatory role we searched for signaling molecules that associate with EAG protein. We have purified a approximately 95-kDa protein from rat brain membranes that binds to EAG. When co-expressed in mammalian cells this protein coimmunoprecipites with EAG and alters the gating of EAG channels. Expression of this protein is regulated during neuronal differentiation. The protein is identical to the recently reported rat protein epsin, which is an EH domain-binding protein similar to the Xenopus mitotic phosphoprotein MP90. These results show that proteins of the epsin family are modulators of channel activity that may link signaling pathways, or the cell cycle, to EAG and thus to various potassium channel functions.