Figure 2.

Molecular representation of the atomic model of the open BK pore embedded in an explicit POPC phospholipid membrane bathed in a 110 mM KCl aqueous salt solution after 1 ns of MD. The extracellular aqueous phase is on top of the bilayer and the intracellular phase is below the bilayer. The structure embedded into the bilayer was obtained by homology using the 3D structures of KcsA and MthK as templates. The extracellular loop that is into the extracellular aqueous phase was modeled using Loop Search. Potassium ions in the selectivity filter (red spheres) are located in sites S1 and S3. Two opposing monomers of BK are shown using ribbon representation for the secondary structure of the protein. Phospholipid hydrocarbon chains are shown as green sticks. Phosphate atoms are shown as yellow spheres and nitrogen atoms of the phospholipds are shown as blue spheres. Water molecules are drawn as light blue spheres, chloride ions are the green spheres, and the red spheres represent the potassium ions.