title: Insect defensin, an inducible antibacterial peptide, forms voltage-dependent channels in Micrococcus luteus.
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.
authors.affiliation: Laboratoire de Biologie Générale, Université Louis Pasteur, URA 1490 Centre National de la Recherche Scientifique Bases Cellulaires et Moléculaires de la Réponse Immunitaire des Insectes, Strasbourg, France.
authors.forename: S
authors.initials: S
authors.lastname: Cociancich
authors.forename: A
authors.initials: A
authors.lastname: Ghazi
authors.forename: C
authors.initials: C
authors.lastname: Hetru
authors.forename: J A
authors.initials: JA
authors.lastname: Hoffmann
authors.forename: L
authors.initials: L
authors.lastname: Letellier
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001798:Blood Proteins / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D023082:Defensins; D006863:Hydrogen-Ion Concentration; D007313:Insecta; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D016982:Micrococcus luteus / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D009994:Osmolar Concentration; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D013696:Temperature
chemical_list: D000900:Anti-Bacterial Agents; D001798:Blood Proteins; D023082:Defensins; D007473:Ion Channels; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D011188:Potassium