Discovery of a novel antimicrobial peptide using membrane binding-based approach

Most known antimicrobial peptides (AMPs) can bind to bacterial cells as the first step to exert their antimicrobial activity. Based on this membrane-binding activity, a novel antimicrobial peptide MDpep9 with the sequence Lys-Ser-Ser-Ser-Pro-Pro-Met-Asn-His was purified from housefly larvae. MDpep9 effectively inhibited the growth of the test bacteria (Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Shigella dysenteria, Pseudomonas aeruginosa, Bacillus subtilis, and Streptococcus pneumoniae), with MIC (minimal inhibitory concentration) values ranged from 9 to 72 μg/ml. Among these bacteria, the Gram-positive bacterium, B. subtilis 9372 was the most sensitive. Furthermore, the antimicrobial mode study showed that cytoplasmic cell membrane is the target for MDpep9 which can exert its antimicrobial action by disrupting and disintegrating bacterial cell membranes, leading ultimately to loss of cytoplasmic membrane integrity. Moreover, the acidic environment around bacterial cell membrane induced molecular unfolding and increased surface hydrophobicity of MDpep9, promoting the interaction of peptide with bacterial lipid membrane. Our results indicate membrane-binding strategy opens the road to simple and cheap large-scale production of a safe antimicrobial peptide from housefly.