Interaction of Poly(l-arginine) with Negatively Charged DPPG Membranes: Calorimetric and Monolayer Studies

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• 作者：Christian Schwieger ; Alfred Blume
• 刊名：Biomacromolecules
• 出版年：2009
• 出版时间：August 10, 2009
• 年：2009
• 卷：10
• 期：8
• 页码：2152-2161
• 全文大小：272K
• 年卷期：v.10,no.8(August 10, 2009)
• ISSN：1526-4602

文摘

The interaction of poly(l-arginine) (PLA) with dipalmitoyl-phosphatidylglycerol (DPPG) bilayer membranes and monolayers was studied by differential scanning calorimetry (DSC), isothermal titration calorimetry (ITC), and monolayer experiments. The binding of PLA affected the main transition temperature of lipid bilayers (T_m) only marginally. Depending on the PLA chain length, T_m was slightly increased or decreased. This finding was attributed to the superposition of two counteracting effects on the transition after PLA binding. The main transition enthalpy (ΔH_m) was decreased upon PLA binding and the formation of a ripple phase (P_β′) was suppressed. ITC experiments showed that two distinct processes are involved in binding of PLA to gel phase (L_β′) membranes. At low peptide content the binding reaction is endothermic, and at high peptide concentration the binding becomes exothermic. However, the enthalpy of binding to fluid (L_α) membranes was exothermic for all peptide-to-lipid ratios. The temperature dependence of PLA binding to fluid palmitoyl-oleoyl-phosphatidylglycerol (POPG) membranes showed a decrease in binding enthalpy with increasing temperature (Δ_RC_p < 0), indicating hydrophobic contributions to the free energy of binding. For longer PLA chains, the binding enthalpy for L_α membranes was more exothermic than for shorter chains. Monolayer adsorption experiments showed two consecutive binding processes. At low initial surface pressures (π₀) a condensation of the lipid film (Δπ < 0) is first observed after PLA injection into the subphase, followed by an increase in film pressure (Δπ > 0) due to insertion of peptide side chains into the monolayer. At higher π₀ only an increase in film pressure can be observed due to the insertion of the side chains. Δπ increases with increasing π₀. The insertion of the peptide into the monolayer is corroborated by the observed shift of π−A isotherms to higher molecular areas. All presented experiments show that the binding of PLA to DPPG membranes has not only electrostatic but also nonelectrostatic contributions.