Effects Of Benzene Ring Structure On Antibacterial Activity Of Protonectin

In recent years,the emergence and widespread of durg-resistant bacteria decreased the bactericidal activity of the drugs which had good activities against bacteria originally.Therefore,it is necessary to design new molecules with good antibacteria activities to alleviate the issue of bacterial resistance.Antimcirobial peptides,as constituents of the first line of defense of organisms' immune system,have broad spectrum activities of anti-bacteria,anti-viruses,anti-fungi,anti-parasites,anti-cancer and other activities,and they are nto produce drug resistance of bacteria.As a result,antimicrobial peptides are promising to become a new type of antibiotic and apply to clinical field.Protonectin has good antibacteria activity.It is a cationic antimicrobial peptide which is originally isolated from the new tropical hornet Agelaia pallipes.Protonectin's amino acid sequence is ILGTILGLLKGL-NH2.Polybia-CP is a nature analogue of protonectin.It is a cationic antimicrobial peptide isolated from the Hornet Polybia paulista venom,and polybia-CP's amino acid sequence is ILGTILGLLKSL-NH2.The two peptides have similar antibacteria activity,while the main difference of protonectin and polybia-CP is located in side chain of the 11 th amino acid,which indicated that this site is not a key site.Therefore,this study focused on the side chain of this amino acid by introducing different side structure to explore the effect of other side chain structure of natural amino acids on the antibacterial activity of protonectin.The result demonstrated protonectin's analogs that containing benzene structure in the side chain of the 11 th amino acid.did not exhibit inhibitory activity against Gram-negative bacteria at 256?M,while the minimum inhibitory concentration of its analogs against Gram-positive bacteria was 2?M to 4?M,showing excellent selectivity.However,the introduction of other structure,such as Hydroxymethyl,methyl and other stuctures,have little effect on the antimicrobial activity of protonectin.Then the possible mechanism of this phenomenon was discussed.In view of the significant difference between Gram-negative bacteria and Gram-positive bacteria is the lipopolysaccharide structure.The lipopolysaccharide(LPS)of Gram negative bacteria is considered to be a major barrier for antibacteria agents.Antimirobial experiments,colony count assays,PI intake experiments and bacterial cell activity experiments indicated that LPS inhibited the activities of Protonectin and its three analogues against Gram negative bacteria.To conclude,the introduction of benzene ring structure to 11 th amino acid side chain leads to protonectin exhibiting excellent selectivity for Gram-negative and Gram-positive bacteria.In addition,the combination of LPS and antimicrobial peptides reduces its activity against Gram negative bacteria.Those discoveries provide a theoretical basis on the relationship between structure and efficacy,mechanism and selective transformation of antibacteria peptides.