Characterization of the antimicrobial activity of mycosubtilin on the plasma membranes. A biomimetic approach

Mycosubtilin, an antimicrobial lipopeptide, is produced by Bacillus subtilis strains. It belongs to the iturin family, which is characterized by the presence of a peptide part, constituted of a constant chiral amino acid sequence cycled by a β-amino fatty acid (Fig. 1).
As all the iturinic lipopeptides, mycosubtilin exhibits its biocide activities on cytoplasmic membrane of target cells [1]. Recently, the activity of mycosubtilin on pathogenic strains resistant to classical agents was shown [2]. However, despite many works focused on its structure and the optimization of its production, only a few studies are conducted to analyze mycosubtilin-membrane interactions.
The purpose of our work was to better understand, at the molecular level, the mechanisms of the mycosubtilin activity on cytoplasmic membranes. Firstly, we modelled the mycosubtilin-membrane interactions by using biomimetic monolayers and their associated techniques (tensiometry and PM-IRRAS). After characterizing the interfacial properties of pure mycosubtilin [3], we used Langmuir films to investigate the mycosubtilin behavior when the lipopeptide reaches the external leaflet of the membrane. We found that the mycosubtilin adsorption to lipid monolayers depended on their lipid composition and the lipopeptide interaction with the membrane was facilitated by the presence of sterols. Then, we mimicked the insertion of the lipopeptide in the whole membrane by using multilamellar vesicles. FT-IR spectroscopy analysis showed that the interaction of mycosubtilin with the artificial membranes induced conformational changes of the lipopeptide only in the presence of sterol.
1. Maget-Dana R, Peypoux F. (1994) Toxicology 87:151-74.
2. Fickers P, Guez JS, Damblon C, Leclère V, Béchet M, Jacques P, Joris B. (2009) Appl. Environ. Microbiol. 75:4636-40.
3. Nasir MN, Thawani A, Kouzayha A, Besson F. (2010) Colloids Surf. B Biointerfaces 78 :17-23.