期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：3
页码：E303-E310
DOI：10.1073/pnas.1417703112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceAntimicrobial peptides (AMPs) help to kill invading bacteria on skin and lung surfaces. We are developing fluorescence microscopy assays that reveal the mechanisms of action of AMPs in real time. It is increasingly clear AMP damage to bacterial cells goes far beyond permeabilization of membranes. Here we demonstrate that for Escherichia coli in aerobic conditions, the peptide CM15 [combining residues 1-7 of cecropin A (from moth) with residues 2-9 of melittin (bee venom)], induces a burst of biochemically harmful reactive oxygen species within 30 s of membrane permeabilization. In anaerobic conditions, CM15 is 20-fold less potent. AMP efficacy in vivo may be tuned to the local level of oxygenation. Antibiotics target specific biochemical mechanisms in bacteria. In response to new drugs, pathogenic bacteria rapidly develop resistance. In contrast, antimicrobial peptides (AMPs) have retained broad spectrum antibacterial potency over millions of years. We present single-cell fluorescence assays that detect reactive oxygen species (ROS) in the Escherichia coli cytoplasm in real time. Within 30 s of permeabilization of the cytoplasmic membrane by the cationic AMP CM15 [combining residues 1-7 of cecropin A (from moth) with residues 2-9 of melittin (bee venom)], three fluorescence signals report oxidative stress in the cytoplasm, apparently involving O2-, H2O2, and [bullet]OH. Mechanistic studies indicate that active respiration is a prerequisite to the CM15-induced oxidative damage. In anaerobic conditions, signals from ROS are greatly diminished and the minimum inhibitory concentration increases 20-fold. Evidently the natural human AMP LL-37 also induces a burst of ROS. Oxidative stress may prove a significant bacteriostatic mechanism for a variety of cationic AMPs. If so, host organisms may use the local oxygen level to modulate AMP potency.
