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Protonation State-dependent Interaction of Polycationic Polymyxins with the Pseudomonas aeruginosa Outer Membrane
Luigi Cutarella1, Alvaro G Temprano1,2,3, Andrea Tafi1
1Department of Biotechnology, Chemistry and Pharmacy, University of Siena, 53100 Siena, Italy.
Abstract:
The rapid spread of antimicrobial resistance (AMR) has relaunched Colistin A, a member of the polycationic polymyxin (PMBs) family, as a last resort option against infection by Gram-negative pathogens such as Pseudomonas aeruginosa. However, the presence of positively charged α,γ-Diamino Butyric acid (Dab) moieties in PMBs is associated with clinical toxicity, so efforts have been made toward the development of derivatives with a reduced total charge. In this study, we used all-atom molecular dynamics (MD) simulations to elucidate the interaction of PMBs with an evolved model of the P. aeruginosa outer membrane (OM) that includes Lipid A and the entire oligosaccharide core. To investigate the potential effects of pH and total charge on OM perturbation by Colistin A, used as a model scaffold, four different protonation states were studied. Results reveal that the Colistin A equipped with an overall +2 formal charge deeply penetrates the OM, displaces Ca2+ ions within the simulated time scale, and destabilizes OM integrity with a higher efficacy than other protonation states. These results highlight the importance of the total charge of small molecules directed toward the OM of Gram-negative pathogens such as P. aeruginosa, providing additional insights into the mechanism of action of Colistin A, essential for guiding the rational design of effective PMB derivatives.
Insights
Colistin A with a +2 charge effectively penetrates the outer membrane of Pseudomonas aeruginosa, displacing calcium ions and destabilizing membrane integrity. This highlights the importance of charge in designing new antimicrobial polymyxin derivatives.
Area of Science:
- Biochemistry
- Molecular Biology
- Computational Chemistry
Background:
- Antimicrobial resistance (AMR) necessitates the use of last-resort antibiotics like Colistin A.
- Polymyxin B derivatives (PMBs) face toxicity concerns due to positively charged moieties, driving research into reduced-charge alternatives.
- Pseudomonas aeruginosa poses a significant threat due to its Gram-negative outer membrane.
Purpose of the Study:
- To elucidate the interaction mechanism of PMBs with the P. aeruginosa outer membrane (OM) using molecular dynamics (MD) simulations.
- To investigate the impact of pH and total charge on OM perturbation by Colistin A.
- To guide the rational design of novel, effective PMB derivatives with reduced toxicity.
Main Methods:
- All-atom molecular dynamics (MD) simulations were employed.
- An evolved model of the P. aeruginosa OM, including Lipid A and the complete oligosaccharide core, was utilized.
- Four distinct protonation states of Colistin A were simulated to assess charge-dependent interactions.
Main Results:
- Colistin A with a +2 formal charge demonstrated deep penetration into the OM.
- The +2 charged Colistin A displaced Ca2+ ions and destabilized OM integrity more effectively than other protonation states.
- Results underscore the critical role of total charge in the efficacy of OM-targeting molecules.
Conclusions:
- The total charge of small molecules is crucial for targeting the OM of Gram-negative pathogens like P. aeruginosa.
- Understanding Colistin A's mechanism of action, particularly charge-dependent interactions, is vital for developing improved PMB derivatives.
- This study provides key insights for designing safer and more effective antimicrobial agents against resistant bacteria.
