Transmission electron microscopic observations of membrane effects of antibiotic cecropin B on Escherichia coli.
The pathway of cell membrane lysis by the peptide antibiotic cecropin B (CB), which contains both a hydrophobic and an amphipathic alpha-helix, was analysed by assessing the morphological changes of Escherichia coli following treatment with the peptide. Exposure of green fluorescent protein (GFP)-expressing E. coli to CB does not lead to an efflux of GFP. Moreover, transmission electron microscopic (TEM) examination of cecropin B-treated cells showed that severe swelling precedes cell death and that the outer membrane becomes distended away from the plasma membrane. Using immuno-gold staining and TEM of E. coli expressing the maltose-binding protein in the cytoplasm, it was apparent that the protein remains restricted to the cytoplasmic compartment. These observations suggest that CB causes gross disruption of the outer membrane of Gram-negative bacteria. Circular dichroism measurements of CB in the presence of cell membrane-mimicking liposomes showed that CB forms secondary structure dependent on the ratio of [lipid]/[peptide]. These observations from this study are important for the future design of custom antimicrobial peptides.
Institute of BioAgricultural Sciences, Academia Sinica, Taipei, Taiwan 115.
Hueih Min
HM
Chen
Shiu-Chiu
SC
Chan
Jao-Chang
JC
Lee
Chia-Ching
CC
Chang
Marudhamuthu
M
Murugan
Ralph W
RW
Jack
D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects* / Q000473:pathology / Q000648:ultrastructure*; D004926:Escherichia coli / Q000187:drug effects* / Q000648:ultrastructure; D049452:Green Fluorescent Proteins; D007150:Immunohistochemistry; D019476:Insect Proteins / Q000494:pharmacology*; D008081:Liposomes / Q000378:metabolism; D008164:Luminescent Proteins; D008854:Microscopy, Electron
D000890:Anti-Infective Agents; D019476:Insect Proteins; D008081:Liposomes; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; C031162:cecropin B protein, Insecta