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Bacterial susceptibility and resistance to modelin-5
Sarah R Dennison1, Leslie Hg Morton1, Kamal Badiani2
1School of Pharmacy and Biomedical Sciences, University of Central Lancashire, Preston PR1 2HE, UK. srdennison1@uclan.ac.uk.
Abstract:
Modelin-5 (M5-NH2) killed Pseudomonas aeruginosa with a minimum lethal concentration (MLC) of 5.86 μM and strongly bound its cytoplasmic membrane (CM) with a Kd of 23.5 μM. The peptide adopted high levels of amphiphilic α-helical structure (75.0%) and penetrated the CM hydrophobic core (8.0 mN m-1). This insertion destabilised CM structure via increased lipid packing and decreased fluidity (ΔGmix < 0), which promoted high levels of lysis (84.1%) and P. aeruginosa cell death. M5-NH2 showed a very strong affinity (Kd = 3.5 μM) and very high levels of amphiphilic α-helical structure with cardiolipin membranes (96.0%,) which primarily drove the peptide's membranolytic action against P. aeruginosa. In contrast, M5-NH2 killed Staphylococcus aureus with an MLC of 147.6 μM and weakly bound its CM with a Kd of 117.6 μM, The peptide adopted low levels of amphiphilic α-helical structure (35.0%) and only penetrated the upper regions of the CM (3.3 mN m-1). This insertion stabilised CM structure via decreased lipid packing and increased fluidity (ΔGmix > 0) and promoted only low levels of lysis (24.3%). The insertion and lysis of the S. aureus CM by M5-NH2 showed a strong negative correlation with its lysyl phosphatidylglycerol (Lys-PG) content (R2 > 0.98). In combination, these data suggested that Lys-PG mediated mechanisms inhibited the membranolytic action of M5-NH2 against S. aureus, thereby rendering the organism resistant to the peptide. These results are discussed in relation to structure/function relationships of M5-NH2 and CM lipids that underpin bacterial susceptibility and resistance to the peptide.
Insights
Modelin-5 (M5-NH2) effectively kills Pseudomonas aeruginosa by disrupting its cell membrane, but is less effective against Staphylococcus aureus due to lysyl phosphatidylglycerol content. This study reveals M5-NH2
Area of Science:
- Biochemistry
- Microbiology
- Structural Biology
Background:
- Antimicrobial peptides (AMPs) are crucial in combating bacterial infections.
- Understanding the mechanisms of bacterial resistance to AMPs is vital for developing new therapeutics.
- Modelin-5 (M5-NH2) is an AMP with known antimicrobial activity.
Purpose of the Study:
- To elucidate the structure-function relationship of Modelin-5 (M5-NH2) in its interaction with bacterial cytoplasmic membranes (CMs).
- To investigate the differential activity of M5-NH2 against Pseudomonas aeruginosa and Staphylococcus aureus.
- To identify the role of specific membrane lipids in mediating bacterial susceptibility or resistance to M5-NH2.
Main Methods:
- Minimum lethal concentration (MLC) assays to determine peptide efficacy.
- Surface plasmon resonance (SPR) to measure peptide-membrane binding affinity (Kd).
- Circular dichroism (CD) spectroscopy to assess peptide secondary structure.
- Membrane permeabilization and dye release assays to quantify membrane disruption and lysis.
Main Results:
- M5-NH2 exhibited potent activity against P. aeruginosa (MLC 5.86 μM), inducing high levels of cell lysis (84.1%) through deep insertion into the CM.
- M5-NH2 showed significantly lower activity against S. aureus (MLC 147.6 μM), with minimal CM penetration and lysis (24.3%).
- Lysyl phosphatidylglycerol (Lys-PG) in S. aureus membranes was identified as a key factor mediating resistance to M5-NH2, showing a strong negative correlation with peptide insertion and lysis.
Conclusions:
- M5-NH2's membranolytic mechanism involves adopting an amphipathic α-helical structure and destabilizing the bacterial CM.
- The differential susceptibility of P. aeruginosa and S. aureus to M5-NH2 is primarily attributed to the presence of Lys-PG in S. aureus, which inhibits peptide-membrane interaction.
- These findings provide insights into AMP-lipid interactions and offer a basis for designing novel AMPs with improved efficacy against resistant bacteria.
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