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Localized permeabilization of E. coli membranes by the antimicrobial peptide Cecropin A

Nambirajan Rangarajan1, Somenath Bakshi, James C Weisshaar

  • 1Department of Chemistry and ‡Molecular Biophysics Program, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.

Biochemistry
|August 31, 2013
PubMed

Insights

Antimicrobial peptide Cecropin A permeabilizes E. coli membranes, with disruptions occurring faster in dividing cells. This process shows a concentration threshold and lag time, suggesting a nucleation mechanism for membrane damage.

Area of Science:

  • Microbiology
  • Biophysics
  • Cell Biology

Background:

  • Antimicrobial peptides (AMPs) are crucial in innate immunity.
  • Understanding AMPs' membrane interaction mechanisms is vital for developing new therapeutics.
  • Cecropin A is a well-studied model AMP.

Purpose of the Study:

  • To investigate the real-time effects of Cecropin A on bacterial membranes.
  • To determine the kinetics and mechanisms of membrane permeabilization by Cecropin A.
  • To explore factors influencing Cecropin A's antimicrobial activity.

Main Methods:

  • Utilized time-resolved fluorescence microscopy to observe single E. coli cells.
  • Employed fluorescent reporters (periplasmic GFP, Sytox Green) to monitor membrane integrity.
  • Performed Monte Carlo simulations to model membrane pore formation.

Main Results:

  • Cecropin A permeabilizes both the outer membrane (OM) and cytoplasmic membrane (CM) of E. coli.
  • Membrane permeabilization exhibits a concentration threshold and lag time.
  • Septating cells and curved membrane surfaces are preferentially targeted.
  • OM permeabilization leads to rapid CM permeabilization.

Conclusions:

  • Cecropin A induces membrane damage through a process potentially involving nucleation.
  • The observed lag times and threshold concentration suggest a complex initiation mechanism.
  • Cecropin A rapidly increases membrane permeability, comparable to large pores or multiple small pores.

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