Structural Determination of Kvβ by Cryogenic Electron Microscopy

Voltage-gated potassium (Kv) channels are tetrameric assemblies with cytosolic N- and C- termini. By attaching to a portion of the N terminus of channel polypeptides, auxiliary Kvβ subunits form complexes with Kv channels (Yang, 2001). Kvβ subunits have a 4:4 stoichiometry with Kv channels, but structural analyses of Kv proteins without Kv channels have revealed more than one oligomeric assembly: a tetrameric or octameric complex (Spear, 2015). Here we seek to discover a complete and coherent picture of the Kvβ subunit in hopes to develop a greater understanding of how the different molecular architectures of Kvβ are used to modulate Kv channel trafficking and potassium transport activities. In the present investigation, we have cloned, expressed, and purified Kvβ for biochemical characterization. Additionally, the Kvβ proteins have been imaged by cryogenic electron microscopy (cryo-EM) to determine the structure of the complex and characterize the tetramer/octamer equilibrium. The latter studies are ongoing. We hypothesize that the equilibrium between the octamer and tetrameric forms of Kvβ and the subsequent binding to Kv channels in vivo, represents a new mechanism for the regulation of Kv channel activity by Kvβ.