In this study, we investigated how the presence of anionic lipids influenced the stability and folding properties of the potassium channel KcsA. By using a combination of gel electrophoresis, tryptophan fluorescence and acrylamide quenching experiments, we found that the presence of the anionic lipid phosphatidylglycerol (PG) in a phosphatidylcholine (PC) bilayer slightly stabilized the tetramer and protected it from trifluoroethanol- induced dissociation. Surprisingly, the presence of phosphatidic acid (PA) had a much larger effect on the stability of KcsA and this lipid, in addition, significantly influenced the folding properties of the protein. The data indicate that PA creates some specificity over PG, and that it most likely stabilizes the tetramer via both electrostatic and hydrogen bond interactions
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