Model of BK α in the absence and presence of β1. BK α S1–S6 was built by homology modeling based on the crystal structure of the Kv1.2/Kv2.1 chimera (Protein Data Bank accession no. 2R9R), using the SWISS-MODEL server (Schwede et al., 2003; Arnold et al., 2006; Kiefer et al., 2009). We used PyMol and Coot (Emsley and Cowtan, 2004) to build S0, TM1, and TM2 as ideal α helices and manually docked them into S1–S6, avoiding steric overlap, but we did not minimize the energy of the structure. The model shows the displacement of the intracellular flank of S0 when β1 is coexpressed with α. Each subunit has a unique color. β1 TM1 and TM2 are black. (A and C) α alone. (B and D) α + β1.