Chain Length and Temperature Dependence of the Reversible Association of Model Acylated Proteins with Lipid Bilayers

To study the binding of fatty-acylated proteins to lipid bilayers, we have specifically attached fatty acids to the N-terminus of chemically modified bovine pancreatic trypsin inhibitor. This was accomplished by reacting the protein with saturated fatty acid anhydrides ranging in length from 8 to 18 carbons. Following radiolabeling of the fatty-acylated proteins at Lys-15, binding of these proteins to palmitoyloleoyl phosphatidylcholine vesicles was examined as a function of temperature using ultracentrifugation to determine the fraction of bound protein. Binding of these fatty-acylated proteins exhibited a significant enthalpy change. We also examined the free-energy change of binding as a function of fatty acid chain length. Our results are complimentary to other binding studies of fatty-acylated peptides. Comparisons with other myristoylated proteins and peptides indicate that local protein structure, apart from electrostatic interactions, plays a significant role in determining the magnitude of the overall free-energy change of membrane binding of fatty-acylated proteins. Light-scattering experiments indicated that both myristoyl and palmitoyl groups can induce protein micelle formation in aqueous solution at high concentration, but that only palmitoyl groups do so at physiologically relevant concentrations. Our results support a model in which single lipid modifications are incapable of stably anchoring proteins to biological membranes but facilitate protein associations in conjunction with other modes of interaction.