Membrane interactions of natural cyclic lipodepsipeptides

Cyclic lipodepsipeptides (CLPs) are a diverse group of secondary metabolites produced by various bacteria with important biological functions, but with yet unresolved molecular mechanisms. Our previous efforts have gone towards characterizing with NMR the conformation and self-assembling properties of a collection of CLPs known as the viscosin group. [1-4] CLPs increasingly attract attention because of their antifungal and antibiotic properties through membrane permeabilization. A full understanding of their membrane interactions is essential to elucidate the exact working mechanism of CLPs. To obtain comprehensive structural information in a membrane environment, we have used liquid-state NMR and model membrane systems, such as micelles and isotropic lipid bicelles. Like micelles, isotropic bicelles display favourable NMR relaxation properties, while possessing structural characteristics of lipid bilayers. [5] The orientation and insertion depth of CLPs in a membrane environment can be investigated using diffusion NMR and paramagnetic relaxation enhancement measurements. The latter is achieved by introducing paramagnetic probes at various locations. By introducing a water-soluble paramagnetic complex to a bicelle sample, NMR signals from nuclei closer to the aqueous phase can be identified. Adding lipid molecules with covalently linked paramagnetic radicals at various positions deliver the orientation and the insertion depth of the peptides in the bilayer. Finally, 31P longitudinal relaxation measurements allow to obtain detailed information regarding the local dynamics of the lipid head groups of the bicelles. [6] The NMR results are complemented with other experimental techniques, including fluorescence spectroscopy, circular dichroism and infrared spectroscopy. We have also performed all-atom molecular dynamics (MD) simulations of CLPs within lipid membranes, which can be confronted with the experimental NMR results. References 1. Sinnaeve, D., Hendrickx, P.M. et al., Chemistry - A European Journal, 2009, 15(46): 12653-12662 2. Sinnaeve, D., Delsuc, M.-A. et al., Chemical Science, 2012, 3: 1284-1292 3. De Vleeschouwer, M., Sinnaeve D. et al., Chemistry - A European Journal, 2014, 20(25): 7766-7775 4. Geudens N., De Vleeschouwer M. et al., ChemBioChem, 2014, 15: 2736-2746 5. Durr, U. H., Gildenberg M. et al., Chem Rev, 2014, 112(11): 6054-6074 6. Bodor, A., Kover, E et al., BBA Biomembranes, 2015, 1848(3): 760-766

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