Membrane thickness (Å) Remove/add Water Animation of K+ Transport
Part i - K+ Ligands
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Part ii - Selectivity
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Structure of the KcsA K+ channel from Streptomyces lividans
The initial view of the potassium channel tetramer is from the plane of the membrane. Each subunit is colored separately and contains three a-helices. The long inner and outer helices span the bilayer membrane. The selectivity pore residues (Sticks, colored white) are in the turn that connects the short pore helices to the inner helices. Waters are shown as small red balls on the extracellular side (top) and in the cytosol (bottom). The K+ ions are shown spacefill, colored dark green.
The membrane thickness indicated is the apolar region of the membrane.
Simple View: Only three of the subunits are shown to provide a clearer view of the pore. Residues 75-79 comprise the selectivity pore and are shown as Sticks, colored CPK. The mainchain C=O's of these residues coordinate the K+ ions. The water-filled cavity is colored cyan. All of the waters shown here are highly-ordered and thus differ from the "bulk" water surrounding the channel.
The refined structure of the potassium channel is described by: