Cell experiment:

Escherichia coli cells are incubated with magainin 2 (50 μg /mL). The cultures are acquired after incubation for 0, 2, 4, 6, and 8 h, respectively, and spread onto LB agar plates, and then the colony-forming units are counted after incubation for 24 h at 37℃. The percentage survival is determined relative to the control treatment[1].

Magainin 2 is an antimicrobial peptide discovered in the skin of Xenopus laevis.

Magainin 2 exhibits bactericidal effects and induces morphological changes in Escherichia coli regarding early apoptosis. Magainin 2 induces the expression of a bacterial protein with affinity for the caspase substrate and effects the expression of RecA as a caspase-like protein[1]. Magainin 2 kill bacteria by permeabilizing the cell membranes without exhibiting significant toxicity against mammalian cells. The main target of the peptide is considered to be the lipid matrix of the membranes. Application of 10 μg /mL magainin 2 to Paramecium caudatum, a protozoan, in pond water caused an osmotic swelling of the cell and a subsequent cell burst, suggesting that the peptide could perturb membrane functions responsible for osmotic balance[2]. Magainin 2 permeabilizes bacterial and mammalian membranes in significantly different ways. The peptide forms pores with a diameter of about 2.8 nm (less than 6.6 nm) in B. megaterium, and translocates into the cytosol. In contrast, the peptide significantly perturbes the membrane of CHO-K1 cells, permitting the entry of a large molecule (larger than 23 nm) into the cytosol, accompanied by membrane budding and lipid flip-flop, mainly accumulating in mitochondria and nuclei[3].

[1]. Lee W, et al. Magainin 2 induces bacterial cell death showing apoptotic properties. Curr Microbiol. 2014 Dec;69(6):794-801. [2]. Matsuzaki K, et al. Magainins as paradigm for the mode of action of pore forming polypeptides. Biochim Biophys Acta. 1998 Nov 10;1376(3):391-400. [3]. Imura Y, et al. Magainin 2 in action: distinct modes of membrane permeabilization in living bacterial and mammalian cells. Biophys J. 2008 Dec 15;95(12):5757-65.