Images of oligomeric Kvβ2, a modulatory subunit of potassium channels

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Abstract
The Shaker type voltage‐gated potassium (K+) channel consists of four pore‐forming Kvα subunits. The channel expression and kinetic properties can be modulated by auxiliary hydrophilic Kvβ subunits via formation of heteromultimeric Kvα‐Kvβ complexes. Because each (Kvα)4 could recruit more than one Kvβ subunit and different Kvβ subunits could potentially interact, the stoichiometry of α‐β and β‐β complexes is therefore critical for understanding the functional regulation of Shaker type potassium channels. We expressed and purified Kvβ2 subunit in Sf9 insect cells. The purified Kvβ2, examined by atomic force and electron microscopy techniques, is found predominately as a square‐shaped tetrameric complex with side dimensions of 100×100 Å2 and height of 51 Å. Thus, Kvβ2 is capable of forming a tetramer in the absence of pore‐forming α subunits. The center of the Kvβ2 complex was observed to be the most heavily stained region, suggesting that this region could be part of an extended tubular structure connecting the inner mouth of the ion permeation pathway to the cytoplasmic environment.