LAUSR

The coupling between membrane proteins and their surrounding lipid bilayer make understanding the membrane lipid regulation of membrane proteins key to understanding their function. The membrane lipid regulation of membrane protein function ranges from specific lipid binding to more general lipid bilayer regulation. The latter mechanism arises from energetic coupling between the lipid bilayer and membrane protein where protein conformational change will alter the organization of the adjacent bilayer. To gain insight into, and tease apart, the specific and general mechanism(s) of membrane protein regulation by the membrane lipids, we examine how the prototypical bacterial potassium channel, KcsA, is regulated by bilayer modifying compounds and drugs using a fluorescence-based technique. The concentration ranges at which the compounds alter the lipid bilayer is determined using gramicidin channels as probes. Comparing the concentration ranges at which molecules alter KcsA function and lipid bilayer properties, enable us to determine whether the underlying mechanism primarily involves specific interactions with KcsA or is bilayer-mediated. Most compounds tested slowed activation and accelerated inactivation at concentrations below those where they alter bilayer properties, suggesting that KcsA likely has a non-specific site that allows hydrophobic molecules to bind and alter channel properties. This site may be the fenestrations proposed to be located on the cytosolic side of aqueous pore of potassium channels (and evident in the x-ray structure). The same compounds alter KcsA function at the concentrations where they alter lipid bilayer properties. These, bilayer-modifying, molecules slow recovery from inactivation at concentrations at which they alter bilayer properties. These results suggest that conformational changes responsible for recovery from inactivation are regulated by a bilayer-mediated mechanism. Our results point to a complicated relationship between direct and bilayer-mediated mechanisms, which both are rather non-specific and may affect a diverse range of ion channels.