The Sensing Sites for the Membrane Inner Lipids Regulate the Activation Gating of the KcsA Potassium Channel

Abstract

The activity of the ion channels are influenced by membrane lipid compositions and specific lipid molecules are indispensable for maintaining channel activities. For the KcsA potassium channel, the presence of anionic phospholipids such as phosphatidylglycerol (PG) is prerequisite for the channel activity. Previously we demonstrated by means of single-channel current recordings in the asymmetric lipid bilayer that the PG molecule on the inner leaflet, rather than the outer leaflet, renders the KcsA channel highly active. The fluorescent method revealed that the helix-bundle gate is kept open in the PG liposome but not much in the liposomes made of neutral or cationic phospholipids. To elucidate the underlying mechanism of the interaction between anionic lipids on the inner leaflet and the activation gate, charge-neutralizing mutations to positively charged residues were introduced. Several amino acid residues lying at the inner boundary of the membrane were found to be sensitive to the PG effect on the gating. Mechanism underlying lipid-mediated regulation of the activation gating of the KcsA channel will be discussed.