Principle investigator: Christiane A. Helm
Co-supervisor: U. Bornscheuer

Effects of ROS include the oxidation of amino acids in proteins and the oxidation of polyunsaturated fatty acids in lipids. Also, both ROS and RNS may induce partial decomposition. We plan to investigate how these changes on a molecular level influence the ensemble. We use model membranes, lipid monolayers at the air-water interface with and without adsorbed polyelectrolytes or proteins. Changes of the surface charge, the crystalline structure of ordered alkyl chains and surface homogeneity are monitored with isotherms, X-ray diffraction and reflection, fluorescence and Brewster microscopy [1], and infrared spectroscopy with B3 (Brezesinski) [2]. A changed lipid head group leads to a different crystalline structure of the ordered alkyl chains, as does the removal of one alkyl chain. Additionally, the nucleation and growth of lipid domains in the ordered phase are affected. The phase separation on µm-scale is monitored with Brewster microscopy. To image lateral structures on the nm-scale the model membranes are transferred on solid substrates and are imaged with atomic force microscopy (AFM) [4]. The surface charge of lipid layers is determined by surface forces using colloidal probe AFM in aqueous solution [3]. When the altered surface charge is quantified, the equilibrium coverage of adsorbed macromolecules and counterions will be explored [2,3]. We are especially interested in cardiolipins and how their oxidation influences the cytochrome C attachment. This will be studied together with A1 (Lillig), B2 (Scholz), and C2 (Lendeckel).
In the next step, nanocomposite systems consisting of lipid monolayers and adsorbed proteins are exposed to radicals. Repeated exposure to ROS/RNS will lead to fragmentation of the protein, and eventually of the model membrane. Fragmented macromolecules will not only show a changed saturation surface coverage but also different adsorption kinetics. 
Complementary experiments will explore the molecular pathways of macromolecule destruction. For that end, macromolecules in a physiological solution will be exposed to ROS/RNS, adsorbed to a surface and imaged with AFM. The partial destruction of macromolecules will indicate pathways and time scales of destruction. Different ROS/RNS as well as radical scavengers will be explored (together with the biological groups).

Literature

1 Möhwald, H.: Rep. Prog. Phys. (1993) 56, 653.

2 Gröning, A., Ahrens, H., Ortmann, T., Lawrenz, F., Brezesinski, G., Scholz, F., Helm, C.A.: Soft Matter (2011) 7, 6467.

3 Berg, F., Block, S., Drache, S., Hippler, R., Helm, C.A.: J. Phys. Chem. B (2013) 117, 8475. 

4 Greinacher A., Gopinadhan, M., Günter J.U., Omer-Adam, M.A., Strobel, U., Warkentin, T.E., Papastavrou, G., Weitschies, W., Helm, C.A.: Artherioscleros, Thromb. Vasc. Biol. (2006) 26, 2386.

5 Borkovec, M., Papastavrou, G.: Curr. Opinion Colloid Interface Sci. (2008) 13, 429.