Antibacterial Activity And Membrane-active Mechanism Of Antimicrobial Peptide NS And Its Analogues

The misuse of antibiotics has resulted in the emergence of resistant bacteria,and the antibacterial peptides with novel membrane mechanism of action have attracted more and more attention.Currently,more and more people think that antibacterial peptides can be instead of the traditional antibiotics.This study explore the antimicrobial activity and mechanism of action of antimicrobial peptide NS and its anologues.Substance P(SP)belong to the tachykinin family of neuropeptides,which takes part in modulating many physiological responses and exhibites direct antimicrobial activity.To improve its potential as novel therapeutic agent,we designed a series of hybrid antimicrobial peptide analogs.Interestingly,antimicrobial peptide SP6 displayed higher antibacterial activity to E.coli,P.aeruginosa and B.subtilis,but showed low antibacterial activity to S.aureus,while NS displayed higher antibacterial activity to all the tested strains.The research was carried out from the following two aspects: What were the factors leading that analogs SP6 showed different activity to E.coli and S.aureus? And what were the factors leading that SP6 and NS showed different activity to S.aureus?We choosed respectively SP6 and NS as templates,and we have designed peptide analogs by amino acid substitution,truncated polypeptide sequence and the introduction of D-amino acids.The results indicate that analogs SP6-1,NS-1and NS-2 showed higher activity to E.coli,P.aeruginosa and B.subtilis than S.aureus,while peptides SP6-3,NS and NS-3 displayed higher antibacterial activity to all the tested strains,and analog NS-3 exhibited relatively low hemolytic activity.The results of Outer and Inner membranes permeability,Con-focal fluorescence microscopy and Flow cytometry test demonstrated that NS and its analogs was membrane active,the results of the Time-killing,MTT and Flow cytometry test that hydrophobic was an very important factors for the peptides in the interaction with cell membrane.And we achieved the conclusion that the hydrophobic leaded SP6 showing different activity to E.coli and S.aureus,and SP6 and NS showing different activity to S.Aureus.