Monitoring the effects of strong cosolvent hexafluoroisopropanol in investigation of the tetrameric structure and stability of K+-channel KcsA

Adsorption of small chain alcohols into lipid membranes significantly changes the conformational states of intrinsic membrane proteins. In this study, the effects of membrane-active strong cosolvent hexafluoroisopropanol (HFIP) on the intrinsic tetrameric stability of potassium channel KcsA were investigated. Presence of acidic phosphatidylglycerol (PG) in non-bilayer phosphatidylethanolamine (PE) or bilayer phosphatidylcholine (PC) significantly increased the tetrameric stability compared to zwitterionic pure PC bilayers. The stabilizing effect of PG in both lipid bilayers was completely abolished upon deletion of the membrane-anchored N-terminus. Tryptophan fluorescence and circular dichroism experiments indicated that HFIP destabilizes the tetramer possibly via drastic changes in the lateral pressure profile close to the membrane–water interface. The data suggest that HFIP disturbs the ionic, H-bonding and hydrophobic interactions among KcsA subunits where N-terminus presumably plays a crucial role in determining the channel proper folding and tetrameric structure via ionic/H-bond interactions between the helix dipole and the membrane lipids.