Exploring the effect of cholesterol in lipid bilayer membrane on the melittin penetration mechanism.

A vascular mimetic membrane system was used to investigate the effect of cholesterol content in lipid bilayer on the dynamics of the melittin-membrane penetration reaction with real-time monitoring by a piezoelectric sensor and the assessment morphology using atomic force microscopy (AFM). In the presence of 30% cholesterol in a noncharged phosphatidylcholine (PC) phospholipid membrane, KA1 (binding affinity constant) and KA2 (insertion affinity constant) derived from a two-step model decreased significantly. This result suggests that the high dose of cholesterol in phospholipid membrane inhibits both the binding and the insertion of melittin. Next, dynamic laser scattering and AFM were used to verify the structural changes of lipid bilayers in solutions and interfaces, respectively. The superstructures in both 0 and 10% cholesterol lipid bilayers were disrupted with penetration of melittin according to these verifications. However, kinetic analysis reveals that the different mechanisms are dependent on cholesterol, particularly for the insertion step.