Study On Enhancement By Helicity Of Interaction Between Antimicrobial Polypeptides And Bacterial Lipids

Antimicrobial peptides（AMPs）,killing bacteria by disrupting bacterial cell membranes,have the potential to combat drug-resistant bacteria since they have low propensity to induce bacterial resistance.AMPs in plants and animials and in clinical trail mostly display helical structure,however,the impact of helical structure on AMPs’biological propertities are still not elucidated.This thesis aims to disclose the effect of helical structure on the activity of polypeptides,and the main content is divided into two parts as follows:（1）A series of antimicrobial polypeptides with different side chains and different secondary structures were synthesized by ring opening polymerization（ROP）ofα-amino acid-N-carboxyanhydride（NCA）and were tested for their biological properties and bactericidal mechanism.It was demonstrated that,compared with non-helical polypeptides,helical polypeptides showed much stronger antimicrobial activity and much higher selectivity aganist Gram-negative and Gram-positive bacteria,including standard strains and clinically isolated bacterial strains.Helical polypeptides also displayed faster killing dynamics.Take N₃-L₁₀-MMBen as an example,this research has certified that helical polypeptides killed bacteria via disturbing bacetrial cell membranes and showed low propensity to induce bacterial resistance.N₃-L₁₀-MMBen could effectively reduce bacteria burden in a subcutaneous infection model,a cystitis model and a peritonitis model.Toxicity test implied that N₃-L₁₀-MMBen showed low toxicity and good biocompatibility.（2）The results of interaction between antimicrobial polypeptides and lipids have confirmed that helical polypeptides had strong affinity with bacterial lipid phosphatidylglycerol（PG）,while no interaction with phosphatidylserine（PS）,phosphatidylethanolamine（PE）or phosphatidylcholine（PC）.Non-helical polypeptides didn’t show interaction with PG,PS,PE or PC.Interaction between helical polypeptides and PG was mainly influenced by helicity but not chirality,the species of end groups or side chains.As verified by mechanism research,lamellar structure was formed during the interaction of helical polypeptides and PG.Natural helical AMP LL-37 also showed strong interaction with PG and the existence of lamellar structure was formed as well.Starting from the huge differences in antimicrobial activity and hemolytic activity between helical and non-helical polypeptides,this research found that helical structure could enhance the interaction between antimicrobial polypeptides and PG,and could induce PG rearrangement,which provided a new sight for helical structure.