Binding of cardiolipin to the KcsA channel at the membrane outer leaflet allosterically opens the inner gate

Membrane proteins embedded in the membrane undergo changes in their actions under the influence of membrane lipids. Here, we present a novel type of lipid action on the potassium channel KcsA from Streptomyces lividans. Cardiolipin is present in various cellular membranes, including the host membrane of KcsA. Although the M0 domain, a nontransmembrane helix, is known to sense anionic lipids in the inner leaflet, we found that divalent anionic cardiolipin in the outer leaflet of the membrane interacts with positively charged residues, Arg64 and Arg89, on the extracellular side of the transmembrane domain. This binding propagates its action across the membrane toward the intracellular region of KcsA, thus, opening the inner gate. Such a long-range allosteric effect has not been found for channel-lipid interactions.