Related Experiment Videos
The outer membrane permeability-increasing action of linear analogues of polymyxin B nonapeptide
1Department of Bacteriology and Immunology, University of Helsinki, Finland.
Abstract:
Polymyxin nonapeptides such as polymyxin B nonapeptide (PMBN) are polymyxin-derived deacylated nonapeptides which contain a heptapeptide ring and are known as effective permeabilizers of the outer membrane (OM) of Gram-negative bacteria. In order to assess the role of the cyclic moiety of PMBN in the permeabilization of the OM, the author compared the OM permeabilizing activity of two synthetic linear PMBN analogues with the well-characterized activity of PMBN. While a low concentration (1-3 micrograms/ml) of PMBN was sufficient to sensitize both Escherichia coli and Pseudomonas aeruginosa to hydrophobic probe antibiotics (rifampin, fusidic acid) by a factor of 100, even a high concentration (100 micrograms/ml) of linear arginyl polymyxin B decapeptide sensitized E. coli only by a factor of 3 and did not sensitize P. aeruginosa at all. In identical assays, linear lysyl polymyxin B nonapeptide completely lacked any sensitizing activity. These findings indicate that the cyclic peptide ring is crucial for the OM-permeabilizing activity of polymyxin nonapeptides.
Insights
The cyclic structure of polymyxin B nonapeptide (PMBN) is essential for its outer membrane permeabilization activity. Linear PMBN analogues showed significantly reduced or no ability to sensitize Gram-negative bacteria to antibiotics.
Area of Science:
- Microbiology
- Biochemistry
- Pharmacology
Background:
- Polymyxin nonapeptides (PMBN) are deacylated polymyxin derivatives.
- PMBN effectively permeabilizes the outer membrane (OM) of Gram-negative bacteria.
- PMBN contains a characteristic heptapeptide ring structure.
Purpose of the Study:
- To investigate the role of the cyclic moiety in PMBN's OM permeabilization.
- To compare the activity of PMBN with its linear analogues.
Main Methods:
- Synthesis of two linear PMBN analogues: linear arginyl polymyxin B decapeptide and linear lysyl polymyxin B nonapeptide.
- Assessing OM permeabilization by measuring bacterial sensitization to hydrophobic antibiotics (rifampin, fusidic acid).
- Testing activity against Escherichia coli and Pseudomonas aeruginosa.
Main Results:
- PMBN (1-3 µg/ml) sensitized E. coli and P. aeruginosa 100-fold to antibiotics.
- Linear arginyl polymyxin B decapeptide (100 µg/ml) showed only a 3-fold sensitization in E. coli and no activity in P. aeruginosa.
- Linear lysyl polymyxin B nonapeptide lacked any sensitizing activity.
Conclusions:
- The cyclic peptide ring of PMBN is critical for its outer membrane permeabilizing function.
- Linearization of PMBN significantly diminishes or abolishes its antibacterial potentiating activity.