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Updated: Aug 28, 2025
Antimicrobial Peptides Produced by Selective Pressure Incorporation of Non-canonical Amino Acids
Published on: May 4, 2018
Where Electrostatics Matter: Bacterial Surface Neutralization and Membrane Disruption by Antimicrobial Peptides
Djenana Vejzovic1, Paulina Piller1, Robert A Cordfunke2
1Institute of Molecular Biosciences, University of Graz, Humboldtstrasse 50/III, 8010 Graz, Austria.
Abstract:
The need for alternative treatment of multi-drug-resistant bacteria led to the increased design of antimicrobial peptides (AMPs). AMPs exhibit a broad antimicrobial spectrum without a distinct preference for a specific species. Thus, their mechanism, disruption of fundamental barrier function by permeabilization of the bacterial cytoplasmic membrane is considered to be rather general and less likely related to antimicrobial resistance. Of all physico-chemical properties of AMPs, their positive charge seems to be crucial for their interaction with negatively charged bacterial membranes. Therefore, we elucidate the role of electrostatic interaction on bacterial surface neutralization and on membrane disruption potential of two potent antimicrobial peptides, namely, OP-145 and SAAP-148. Experiments were performed on Escherichia coli, a Gram-negative bacterium, and Enterococcus hirae, a Gram-positive bacterium, as well as on their model membranes. Zeta potential measurements demonstrated that both peptides neutralized the surface charge of E. coli immediately after their exposure, but not of E. hirae. Second, peptides neutralized all model membranes, but failed to efficiently disrupt model membranes mimicking Gram-negative bacteria. This was further confirmed by flow cytometry showing reduced membrane permeability for SAAP-148 and the lack of OP-145 to permeabilize the E. coli membrane. As neutralization of E. coli surface charges was achieved before the cells were killed, we conclude that electrostatic forces are more important for actions on the surface of Gram-negative bacteria than on their cytoplasmic membranes.
Insights
Antimicrobial peptides (AMPs) neutralize Gram-negative bacteria surfaces via electrostatic interactions, but struggle to disrupt their membranes. This suggests charge neutralization is key for AMP efficacy against these pathogens.
Area of Science:
- Microbiology
- Biochemistry
- Drug Discovery
Background:
- Multi-drug-resistant bacteria necessitate novel treatments, driving antimicrobial peptide (AMP) development.
- AMPs possess broad-spectrum activity, with membrane permeabilization as a primary mechanism, theoretically limiting resistance.
- Positive charge on AMPs is critical for interacting with negatively charged bacterial membranes.
Purpose of the Study:
- To investigate the role of electrostatic interactions in bacterial surface charge neutralization and membrane disruption by AMPs.
- To compare the effects of two potent AMPs, OP-145 and SAAP-148, on Gram-negative (Escherichia coli) and Gram-positive (Enterococcus hirae) bacteria and their model membranes.
Main Methods:
- Zeta potential measurements to assess bacterial surface charge neutralization.
- Flow cytometry to evaluate bacterial membrane permeability.
- Experiments conducted on live bacteria (E. coli, E. hirae) and their corresponding model membranes.
Main Results:
- Both OP-145 and SAAP-148 rapidly neutralized the surface charge of E. coli but not E. hirae.
- AMPs effectively neutralized model membranes but showed limited disruption of Gram-negative mimicking membranes.
- Flow cytometry confirmed reduced membrane permeability for SAAP-148 and a lack of permeabilization for E. coli by OP-145.
Conclusions:
- Electrostatic forces are crucial for AMPs' surface action on Gram-negative bacteria.
- AMPs' ability to neutralize bacterial surface charge precedes cell death, highlighting the importance of initial electrostatic interactions.
- The findings suggest electrostatic interactions are more significant for AMPs' effects on Gram-negative bacterial surfaces than for direct cytoplasmic membrane disruption.
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