Effect of antimicrobial apomyoglobin 56-131 peptide on liposomes and planar lipid bilayer membrane

The horse apomyoglobin 56-131 peptide is a convenient object for studies on the recently discovered antimicrobial activities of haem-binding protein fragments called haemocidins. The purpose of this study was to determine the effect of this peptide on planar lipid bilayer membranes and on liposomes of different lipid compositions. Micromolar concentrations of the apomyoglobin 56-131 fragment disrupt phosphatidylserine/phosphatidylethanolamine planar lipid bilayers without discrete conductance changes. The observed detergent-like action is dependent on peptide concentration: the lower amount of peptide resulted in longer bilayer lifetime. The cholesterol has an inhibitory effect on peptide-induced liposome lysis as shown by calcein release from liposomes. Additionally, there was considerable lytic activity on liposomes formed from anionic lipids of the sort found in bacterial membranes. Circular dichroism (CD) experiments showed that the peptide had a disordered structure in aqueous solutions and folds gradually to form helices in both membrane-mimetic trifluoroethanol solutions as well as in liposome suspensions. The features of the apomyoglobin 56 131 fragment that are similar to the cationic antimicrobial peptides acting in a 'carpet-like' manner are discussed. (C) 2001 Elsevier Science B.V. and International Society of Chemotherapy. All rights reserved.