A wide variety of naturally expressed anti-microbial peptides (AMPs) have been discovered in plants, animals, and humans. AMPs are remarkably for their general ability to halt growth of both Gram negative and Gram positive bacteria. Cationic AMPs are known to form amphipathic helices that bind to anionic cell membranes, form pores, and eventually lyse the cell. The relative inability of bacteria to resist this general mode of action makes AMPs and their mimics interesting drug candidates against antibiotic-resistant strains. While it is well established that AMPs degrade bacterial membranes and eventually lead to lysis, most of the mechanistic work has focused either on studies of synthetic vesicles in vitro or on long-time, bulk effects of AMPs on bacteria. The detailed mechanism of AMP attack on bacterial membranes is not well understood. The primary goal of this work is to develop novel fluorescence microscopy assays that directly observe the attack of AMPs on bacterial membranes in real time, for individual cells. For the first time, these methods will enable placement of a number of directly observable events on the same, unified time line covering the first 10 seconds to the first two hours after injection of the AMP. Measured events will include AMP binding density, halting of flagellar motion, cessation of growth, leakage of the periplasm, and leakage of the cytoplasm. Time lapse imaging after removal of the AMP will reveal which symptoms of the attack are reversible and which are not, as well as the time scale on which cells recover growth. The new methods will be used in an exploratory study of the mechanisms by which a variety of different AMPs attack membranes in both the Gram negative E. coli and the Gram positive Bacillus subtilis. These include LL-37, cecropin A, magainin-2, melittin, alamethicin, indolicidin, bactenecin-5, 1-defensin, and protegrin-1. We will directly compare the surface concentrations at which each AMP degrades bacterial cell membranes with results of previous studies in vitro on synthetic lipid bilayers. The results will help determine whether purported carpet- forming and pore-forming mechanisms gleaned from in vitro studies are relevant to real bacterial membranes. The methods developed here will be widely applicable to studies of both AMPs and drug candidates interacting with a variety of bacterial strains.

Public Health Relevance

Bacteria are increasingly resistant to drugs. Antimicrobial peptides are the front-line defense against pathogens throughout the animal kingdom, but we do not really understand how they work to kill bacterial cells. This work will develop novel imaging methods that will enable direct observation of the mechanisms of bacterial killing by antimicrobials with better spatial and time resolution than ever before.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM094510-03
Application #
8313950
Study Section
Biochemistry and Biophysics of Membranes Study Section (BBM)
Program Officer
Chin, Jean
Project Start
2010-08-01
Project End
2014-07-31
Budget Start
2012-08-01
Budget End
2013-07-31
Support Year
3
Fiscal Year
2012
Total Cost
$267,651
Indirect Cost
$79,551
Name
University of Wisconsin Madison
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Agrawal, Anurag; Weisshaar, James C (2018) Effects of alterations of the E. coli lipopolysaccharide layer on membrane permeabilization events induced by Cecropin A. Biochim Biophys Acta Biomembr 1860:1470-1479
Yang, Zhilin; Weisshaar, James C (2018) HaloTag Assay Suggests Common Mechanism of E. coli Membrane Permeabilization Induced by Cationic Peptides. ACS Chem Biol 13:2161-2169
Yang, Zhilin; Choi, Heejun; Weisshaar, James C (2018) Melittin-Induced Permeabilization, Re-sealing, and Re-permeabilization of E. coli Membranes. Biophys J 114:368-379
Yang, Zhilin; Choi, Heejun (2018) Single-Cell, Time-Lapse Reactive Oxygen Species Detection in E. coli. Curr Protoc Cell Biol 80:e60
Mustafi, Mainak; Weisshaar, James C (2018) Simultaneous Binding of Multiple EF-Tu Copies to Translating Ribosomes in Live Escherichia coli. MBio 9:
Choi, Heejun; Yang, Zhilin; Weisshaar, James C (2017) Oxidative stress induced in E. coli by the human antimicrobial peptide LL-37. PLoS Pathog 13:e1006481
Mohapatra, Sonisilpa; Choi, Heejun; Ge, Xueliang et al. (2017) Spatial Distribution and Ribosome-Binding Dynamics of EF-P in Live Escherichia coli. MBio 8:
Choi, Heejun; Chakraborty, Saswata; Liu, Runhui et al. (2016) Single-Cell, Time-Resolved Antimicrobial Effects of a Highly Cationic, Random Nylon-3 Copolymer on Live Escherichia coli. ACS Chem Biol 11:113-20
Li, Wenting; Bouveret, Emmanuelle; Zhang, Yan et al. (2016) Effects of amino acid starvation on RelA diffusive behavior in live Escherichia coli. Mol Microbiol 99:571-85
Choi, Heejun; Rangarajan, Nambirajan; Weisshaar, James C (2016) Lights, Camera, Action! Antimicrobial Peptide Mechanisms Imaged in Space and Time. Trends Microbiol 24:111-122

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