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.
Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
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W
Wang
D K
DK
Smith
K
K
Moulding
H M
HM
Chen
D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000737:chemistry / Q000378:metabolism*; D015374:Biosensing Techniques; D002942:Circular Dichroism; D015195:Drug Design; D017022:Flow Injection Analysis; D019476:Insect Proteins / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D016624:Negative Staining; D010539:Permeability / Q000187:drug effects; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D011485:Protein Binding
D000890:Anti-Infective Agents; D019476:Insect Proteins; D008081:Liposomes; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; C115150:cecropin B1 protein, insect; C115151:cecropin B3 protein, insect; C031162:cecropin B protein, Insecta