alexa Insect defensin, an inducible antibacterial peptide, forms voltage-dependent channels in Micrococcus luteus.
Bioinformatics & Systems Biology

Bioinformatics & Systems Biology

Journal of Proteomics & Bioinformatics

Author(s): Cociancich S, Ghazi A, Hetru C, Hoffmann JA, Letellier L

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Abstract Insect defensins are cationic, cysteine-rich peptides (approximately 4 kDa) that appear after bacterial challenge or injury in the hemolymph of insects belonging to a large variety of orders. These peptides possess anti-Gram-positive activity and participate in the potent antibacterial defense reactions of insects. Using recombinant insect defensin and the strain Micrococcus luteus as a test organism, we have investigated the mode of action of this peptide. We show that defensin disrupts the permeability barrier of the cytoplasmic membrane of M. luteus, resulting in a loss of cytoplasmic potassium, a partial depolarization of the inner membrane, a decrease in cytoplasmic ATP, and an inhibition of respiration. Potassium loss is inhibited below the order-disorder transition of the lipid hydrocarbon chains. It is also inhibited by divalent cations and by a decrease in the membrane potential below a threshold of 110 mV. We propose that these permeability changes reflect the formation of channels in the cytoplasmic membrane by defensin oligomers. This proposal is supported by patch-clamp experiments that show that insect defensins form channels in giant liposomes.
This article was published in J Biol Chem and referenced in Journal of Proteomics & Bioinformatics

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