Abstract
Oxidized phospholipids (OxPls)are involved in numerous pathological conditions. They are formed under oxidative stress and are therefore closely linked to programmed cell death events (apoptosis). Unfortunately, a coherent overall view of the causalities and mechanisms is lacking, mainly because of insufficient understanding of the occurring processes on a cellular and molecular level. In general, OxPLs are the oxidation products of (poly)unsaturated diacyl- and alk(en)ylacyl glycerophospholipids. Their differences in the structure, polarity and shape from their parent molecules can change the biophysical properties and function of membranes. Simultaneously changes in the lipid-protein interactions might result in the alternation of protein functions.To characterize their impact on the organization of lipid membranes and involvement in specific protein-lipid interactions - with respect to protein misfolding but also the function of anti-apoptotic Bcl-2 protein - we study various biological lipid model systems by a combination of Solid State NMR, Circular Dichroism and Calorimetry techniques. DSC measurements revealed significant effects of OxPls on the physical behavior of DMPC bilayer especially at high concentration of OxPls. The size of changes was for all oxidized lipids used clearly visible but differentiated as a function of OxPls species (PazePc, PoxnoPc, POVPC,PGPC). The observed phase transition in these mixed DMPC bilayers were moved to higher temperatures in the presence of heavy water due to condensing effects. Temperature dependent solid state31P NMR lineshapes of lipid headgroups in OxPl-containing DMPC bilayers reflected their complex phase behavior as visible in the thermograms. In addition there was a two phase region visible where two different types of lamellar phases coexist. In addition, 2H solid state NMR was used to characterize the hydration behavior (D2O) at the membrane interface in the presense of OxPls.
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