Cecropin B Research Articles

The Dependence of Membrane Permeability by the Antibacterial Peptide Cecropin B and Its Analogs, CB-1 and CB-3, on Liposomes of Different Composition

A natural antibacterial peptide, cecropin B (CB), and designed analogs, CB-1 and CB-3, were synthesized. The three peptides have different structural characteristics, with CB having one hydrophobic and one amphipathic alpha-helix, CB-1 having two amphipathic alpha-helices, and CB-3 having two hydrophobic alpha-helices. These differences were used as the rationale for a study of their efficacy in breaking liposomes with different combinations of phosphatidic acid and phosphatidylcholine. Biosensor binding measurements and encapsulating dye leakage studies showed that the higher binding affinity of CB and CB-1 to the polar heads of lipids is not necessary for the peptides to be more effective at lysing lipid bilayers, especially when liposomes have a higher phosphatidic acid content. Kinetic studies, by intrinsic and extrinsic fluorescence stopped-flow measurements, revealed two transitional steps in liposome breakage by CB and CB-1, although only one kinetic step was found for CB-3. Circular dichroism stopped-flow measurements, monitoring the formation of secondary structure in the peptides, found one kinetic step for the interaction of all of the peptides with the liposomes. Also, the alpha-helical motif of the peptides was maintained after interacting with the liposomes. Based on these results, the mechanisms of liposome lysis by CB, CB-1, and CB-3 are discussed.

Effects of the anti-bacterial peptide cecropin B and its analogs, cecropins B-1 and B-2, on liposomes, bacteria, and cancer cells

Custom designed analogs of the natural anti-bacterial peptide cecropin B (CB) have been synthesized; cecropin B-1 (CB-1) was constructed by replacing the C-terminal segment (residues 26 to 35) with the N-terminal sequence of CB (positions 1 to 10 which include five lysine residues). The second analog, CB-2, is identical to CB-1 except for the insertion of a Gly-Pro residue pair between Pro-24 and Ala-25. These peptides were used to investigate their anti-liposome, anti-bacterial and anti-cancer activities. The strength of anti-liposome activity is reduced two- to three-fold when the analogs are used instead of natural CB based on DL 50 analysis. Similarly, the potency of these analogs on certain bacteria is about two- to four-fold lower than those of CB based on LC measurements. In contrast, on leukemia cancer cells, the potency of CB-1 and CB-2 is about two- to three-fold greater than that of natural CB based on IC 50 measurements. All CB, CB-1 and CB-2 peptides have comparable helix contents according to CD measurements. These results indicate that the designed cationic lytic peptides, having extra cationic residues, are less effective in breaking liposomes and killing bacteria but more effective in lysing cancer cells. The possible interpretations for these observations are discussed. © 1997 Elsevier Science B.V.