Single Molecular Kinetics During The Interactions Between Melittin And A Cell Membrane

As a typical antimicrobial peptide,melittin kills bacteria by forming transmembrane pores on the cell membrane of bacteria.This unique pore-forming mechanism promises melittin for the development of novel antimicrobial agents that have high efficiency and will not induce drug resistance.However,the practical applications requires deep understanding and effective regulation of the membrane action process of the peptide.Related researches mainly focus on characterizing the changes in morphology and structure of peptides and membrane during their interactions based on the ensemble information of a large number of molecules,while molecular details in the dynamic process are significantly overlooked.In this thesis,the melittin-membrane interactions were investigated from a new perspective of single molecular kinetics.By combining the single-particle tracking and surface-induced fluorescence attenuation techniques,the three-dimensional motions of lipids and peptides were monitored in real time and their correlation with the membrane poration activity of melittin was explored.The adsorption and accumulation of melittin on membrane surface significantly sped up the lateral diffusion of lipids surrounding the membrane-bound peptides,which in turn facilitated the insertion of melittin at such heterogeneous regions.Melittin tended to deform to a“U”shape and displayed several metastable states during inserting into a membrane,before the ultimate formation of toroidal pores with peptides and lipids dynamically transiting between the two leaflets of bilayer.Then,the cell membrane model was further extended to a bi-component phospholipid membrane model,from which we found that melittin tended to work at the boundary region between phase domains,disturb and blur the phase separation behavior and consequently lower the confinement of phase boundary on lipid motions.Our results not only reveal the physical mechanism of membrane poration by melittin,but also pave a new way to probe the dynamical interactions between biomolecules and a cell membrane,and provide crucial hints on the correlation between single-molecular dynamics and the underlying biological processes.