Membrane Interactions of Cyclic Lipodepsipeptides

The use of natural products isolated from microorganisms is becoming a promising alternative approach to control plant diseases caused by phytopathogens. In this respect, cyclic lipodepsipeptides (CLPs) are a diverse group of secondary metabolites produced by various bacteria with interesting biological functions. However, they have yet unresolved molecular mechanisms. CLPs are made up of an amino acid sequence consisting of both D- and L-amino acids. At the N-terminus, they are capped by a fatty acid moiety, in most cases a hydroxydecanoic acid. Depending on chemical properties, such as the amino acid sequence length, the CLPs can be classified into different groups. Our previous efforts have gone towards characterizing the three-dimensional conformations of several CLP groups using liquid-state NMR spectroscopy, X-ray crystallography or both. [1-2] It is believed that CLPs exert their biological functions through interactions with the cellular membrane. However, 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 various, complementary techniques including liquid-state NMR spectroscopy. Using this technique, the affinity, 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, 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 in the membrane. [3] 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 results. 1. Sinnaeve, D., Hendrickx, P.M. et al., Chemistry - A European Journal, 2009, 15(46): 12653 2. Geudens N., De Vleeschouwer M. et al., ChemBioChem, 2014, 15: 2736 3. Bodor, A., Kover, E et al., BBA Biomembranes, 2015, 1848(3): 760