Modulation of the Hydrophobic Domain of Polymyxin B Nonapeptide: Effect on Outer-Membrane Permeabilization and Lipopolysaccharide Neutralization
- 1Department of Organic Chemistry (H.T., M.F.) and 2Chemical Services Unit (M.E.), the Weizmann Institute of Science, Rehovot, Israel; and3Department of Human Microbiology, Sackler Faculty of Medicine, Tel Aviv University, Tel-Aviv Israel (H.T., I.O., S.C.)
- Mati Fridkin, Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot, 76100, Israel. E-mail: mati.fridkin{at}weizmann.ac.il
Abstract
Polymyxin B nonapeptide (PMBN), a cationic cyclic peptide derived from the antibacterial peptide polymyxin B, is capable of specifically increasing the permeability of the outer membrane (OM) of Gram-negative bacteria toward hydrophobic antibiotics. In this study, we evaluated the contribution of the hydrophobic segment of PMBN (i.e.,d-Phe5-Leu6) to this activity. Accordingly, we synthesized four analogs of PMBN by replacingd-Phe5 with either with d-Trp ord-Tyr and Leu6 with Phe or Ala and evaluated their ability to bind cell-free lipopolysaccharide (LPS) and increase bacterial OM permeability. Compared with PMBN, [d-Tyr5]PMBN and [Ala6]PMBN possessed reduced LPS affinity (IC50 = 2.5, 25, and 12 μM, respectively) and significantly reduced OM permeability and LPS neutralization activity. [Phe6]PMBN exhibited rather similar affinity to cell-free LPS (IC50 = 5 μM) and the same OM permeability capacity as PMBN. However, [d-Trp5]PMBN, despite its similar affinity to cell-free LPS (IC50 = 4 μM), had moderately reduced OM permeability capacity. These results demonstrate the significant role of the PMBN hydrophobic segment in promoting biological activity.
Footnotes
- Abbreviations:
- LPS
- lipopolysaccharide
- OM
- outer membrane
- PMB
- polymyxin B
- PMBN
- polymyxin B nonapeptide
- Dab
- 2,4-diaminobutyric acid
- Cbz
- benzyloxycarbonyl
- DMF
- dimethylformamide
- TFA
- trifluoroacetic acid
- HPLC
- high-performance liquid chromatography
- GRAVY
- grand average of hydropathicity
- ISB
- Isotonic Sensitest Broth
- CFU
- colony forming unit
- MIC
- minimal inhibitory concentration
- CD
- circular dichroism
- TNF
- tumor necrosis factor
- IL
- interleukin
- RP-HPLC
- reversed phase–high-performance liquid chromatography
- MM6
- MONO-MAC-6
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- Received April 24, 2002.
- Accepted August 5, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
