Symmetry and Size of Membrane Protein Polyhedral Nanoparticles

faith of a cell are members of the Bcl-2 protein family interacting with the mitochondrial outer membrane (MOM) and modulating its permeability. For the longest time MOM forming lipids have been seen as structural building blocks without any mechanistically importance in apoptosis. This view changed in recent years after evidence for the direct involvement in apoptotic events of oxidized phospholipids (OxPls) formed under intracellular stress has been provided. Since the presence of OxPls strongly influences the equilibrium of proapoptotic Bax protein towards its membrane bound state, we investigate their role in the Bax induced step of membrane pore formation and the undergoing structural changes of Bax protein during this event. We therefore created cell-free MOM mimicking liposome systems who resemble the cellular situation prior and upon oxidative stress. By using differential scanning calorimetry accompanied by 1H, 13C and 31P solid state MAS NMR spectroscopy we could gain insights into the hydrophilic interface region of the membranes as well as their hydrophobic fatty acid regions. Upon incorporation of OxPls both methods revealed drastic changes in the dynamics of the membranes. Additionally we could relate these perturbations caused by lipid oxidation to an increased membrane affinity of pro-apoptotic Bax protein, presumably aiding Bax membrane penetration necessary for successful pore formation. Currently we are investigating the structural changes of Bax protein upon membrane insertion by solid state MAS NMR spectroscopy to gain mechanistically insights in the process of MOM pore formation. First 15N NMR suggest the observation of a Bax-lipid assembly. Structural studies with fully labeled Bax protein are in progress.