Design And Application Of Self-assembled Antimicrobial Peptides

Antimicrobial peptides(AMPs)are a class of small-molecule peptides that fight against external pathogens.Antimicrobial peptides are widely presenting in a variety of organisms and are an important part of the non-specific immune function of organisms.They have various biological functions such as anti-bacteria,fungi,viruses,and tumors.At the same time,the special bactericidal mechanism of antimicrobial peptides makes it difficult for bacteria to develop drug resistance,so they have shown great potential applications in many fields and are expected to become a new type of green antimicrobial molecules or additives.The design and research of antibacterial peptides with strong antibacterial properties,good stability,and good targeting performance are the prerequisites for the development of green antibacterial drugs.However,there are still some problems in the current research on antibacterial peptides,such as poor biological activity,low stability,high biological toxicity,etc.Research in these directions is still very limited.This thesis is mainly focused on the improvement of the stability and antibacterial activity of antibacterial peptides by utilizing a self-assembling strategy.The main research contents of this paper are as follows:Part 1:H.pylori is a common gastrointestinal bacterium that is closely related to the occurrence of gastrointestinal diseases such as chronic gastritis,peptic ulcer,gastric mucosa-related lymphoid tissue lymphoma,gastric cancer,etc.Eradication of H.pylori is very important for the treatment of the related diseases.However,due to the special physiological environment of the stomach and the bacterial resistance to drugs,the efficacy of the drugs is reduced and the expected therapeutic effect cannot be achieved.Studies have found that some natural antibacterial peptides have a good therapeutic effect on H.pylori and are expected to be used to treat related diseases caused by H.pylori.In the first part of this thesis,we designed four self-assembling antimicrobial peptides based on natural antimicrobial peptides.Our study found that these designed antimicrobial peptides had highly effective antimicrobial effects on H.pylori,among which the peptide GE33 had the strongest antimicrobial effect.It was found that GE33 was p H-responsive.Under neutral p H conditions,GE33 could self-assemble into stable peptide fibers.While under acidic conditions,assembled GE33 nanostructures would decompose into oligomers to exert bactericidal functions.In vivo experiments had also proved that GE33 kept good antibacterial properties after entering the gastric environment of mice,and is expected to be developed into a new type of drug molecule for the treatment of gastric diseases.Part 2:Biofilms are widely involved in human lives,such as medical infection,environmental remediation,and industrial processes.However,the control of the biofilm has still been a challenge because of its strong drug resistance ability.Here,we designed and synthesized an amphipathic antimicrobial peptide(Ac-^DK^DH^DH^DQ^DK^DL^DV^DF^DF^DA^DK-NH₂(KKd-11))that was composed of D-amino acids(DAAs).The KKd-11 was found to self-assemble into hydrogel with an improved long-term antimicrobial ability and a better antiprotease activity as compared to the hydrogel formed by Ac-^LK^LH^LH^LQ^LK^LL^LV^LF^LF^LA^LK-NH₂(KK-11).Our results indicated that KKd-11 was not only able to inhibit the formation of biofilms,but also could effectively damage preformed mature biofilms and kill the bacteria within the biofilms.Besides,cell viability assays indicated that KKd-11peptide had very good biocompatibility.Therefore,KKd-11 hydrogel should have great potential in the treatment of biofilm-induced infections.Also,it was found that the two short peptides with the same sequence and opposite chirality would self-assemble into supramolecular nanostructures with different chiral properties;but in a mixed system,the peptides co-assembled into achiral nanofibers.The study of the self-assembly and co-assembly behaviors of the chiral peptides shed light on the complex chiral phenomena in biological systems.