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Structure-function studies of polymyxin B nonapeptide: implications to sensitization of gram-negative bacteria
1Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
Abstract:
Polymyxin B nonapeptide (PMBN), a cationic cyclic peptide derived by enzymatic processing from the naturally occurring peptide polymyxin B, is able to increase the permeability of the outer membrane of Gram-negative bacteria toward hydrophobic antibiotics probably by binding to the bacterial lipopolysaccharide (LPS). We have synthesized 11 cyclic analogues of PMBN and evaluated their activities compared to that of PMBN. The synthetic peptides were much less potent than PMBN in their capacity to sensitize Escherichia coli and Klebsiella pneumoniae toward novobiocin and to displace dansyl-PMBN from Escherichia coli LPS. Moreover, unlike PMBN, none of the analogues were able to inhibit the growth of Pseudomonas aeruginosa. The structural-functional features of PMBN were characterized and identified with regard to the ring size, the distance between positive charges and peptide backbone, the chirality of the DPhe-Leu domain, and the nature of the charged groups. Apparently, the structure of PMBN is highly specific for efficient perturbation of the outer membrane of Gram-negative bacteria as well as for LPS binding. The present study further increases our understanding of the complex PMBN-LPS and may, potentially, enable the design of compounds having enhanced permeabilization potency of the Gram-negative outer membrane.
Insights
Polymyxin B nonapeptide (PMBN) enhances Gram-negative bacterial outer membrane permeability. Its specific structure is crucial for this activity and lipopolysaccharide (LPS) binding, unlike synthesized analogues.
Area of Science:
- Microbiology
- Biochemistry
- Peptide Chemistry
Background:
- Polymyxin B nonapeptide (PMBN) is a derivative of polymyxin B.
- PMBN increases Gram-negative bacterial outer membrane permeability, potentially enhancing antibiotic efficacy.
- Its mechanism involves binding to bacterial lipopolysaccharide (LPS).
Purpose of the Study:
- To synthesize and evaluate cyclic analogues of PMBN.
- To identify the structure-activity relationships of PMBN for outer membrane permeabilization.
- To understand the PMBN-LPS interaction for potential drug design.
Main Methods:
- Synthesis of 11 cyclic analogues of PMBN.
- Evaluation of analogue activity in sensitizing Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae) to novobiocin.
- Assay for dansyl-PMBN displacement from E. coli LPS.
- Assessment of growth inhibition of Pseudomonas aeruginosa.
Main Results:
- All synthesized analogues were less potent than PMBN in sensitizing bacteria and displacing LPS.
- None of the analogues inhibited Pseudomonas aeruginosa growth.
- PMBN's specific structural features (ring size, charge distribution, chirality, charged groups) are critical for its activity.
Conclusions:
- PMBN possesses a highly specific structure essential for its potent Gram-negative outer membrane permeabilization and LPS binding.
- Synthesized analogues did not replicate PMBN's efficacy.
- This research deepens the understanding of PMBN-LPS interactions and may guide the design of novel outer membrane permeabilization agents.