Self-assembly Of Cationic Peptide And The Sustained-release Antimicrobial Activity

Antimicrobial resistance has become one of the most pressing public health concerns worldwide.There has an urgent need for the development of novel classes of antimicrobial agents and materials.Antimicrobial peptides?AMPs?are an integral part of defensive active peptides of the innate immune system that protect a host from invading pathogenic bacteria.As their broad-spectral bactericidal activity,low cytotoxicity and the distinctive mode of action,AMPs are currently being considered as potential candidates for antibiotics.However,it is difficult to deal with the practical application of long-acting antibacterial activity in vivo for the poor stability of the traditional antibacterial peptide,so it is a new research direction to construct cationic self assembled sustained-release peptides.The amyloid peptide KLVFFAE itself has better self-assembly ability and shows stronger destructive effect on cell membrane.Based on the sequence of this segment as the template,combined with the rules of construction self-assembling peptides and the structural characteristics of antimicrobial peptides,we design two cationic amphiphilic self-assembling peptides,KKKFAFAFAFAKKK and KKKKKKFAFAFAFA,focusing on the nanostructures of self-assembly cationic peptides,and testing their antibacterial activity,and further exploring the possibility application of its sustained release antibacterial activity.The main research contents are as follows:?1?Antibacterial activity of cationic peptidesThe secondary structure of the two cationic peptides show random coil structure in PBS solution,and the two cationic peptides present antimicrobial activity and tend to be more selective to Gram-negative bacteria and can rapidly kill the bacteria within4 h.However,they also displayed the different abilities in antimicrobial activity.Compared to peptide K₆?FA?₄,peptide K₃?FA?₄K₃ displayed better antimicrobial activity and wider antimicrobial spectrum.After treated with peptide,the integrity of the E.coli cell membrane is destroyed by the peptide and eventually leads to cell death.The two peptides were nontoxic near the MIC and MBC,and presented their compatibility as novel therapeutic agent.?2?Sustained release of peptide molecules from the nanofibersThe secondary structures of the two peptides incubated at pH=12 were?-helix and?-sheet,respectively.After we switched pH from 12 to 7 in peptide solution,the secondary structures of the two peptides gradually turned into random coil,meanwhile,the nanofibers disassembled into small nanostructure and finally into peptide monomer.The self-assembly of the two peptides was similar,but the disassembly rate of peptide K₃?FA?₄K₃ showed faster than that of peptide K₆?FA?₄.With time increasing,both two peptide fibrils presented better antibacterial activity and the increased antibacterial rate.The bacterial cells can be killed within 5 h initially,and it only took 1 h to complete the sterilization after 48 h disassembling of peptide fibrils.Compared to peptide K₆?FA?₄,peptide K₃?FA?₄K₃ exhibited faster antibacterial rate within 1 day disassembling,whereas after 2 days,both them showed similar antibacterial activity.