Mitochondrial Membrane Organization Under Oxidative Stress: Insight By Solid-State Nmr And Neutron Reflectometry

Virtually every biological process involves membranes. Especially, the mitochondrial outer membrane (MOM) plays a key role in programmed cell death. Opposing members of the Bcl-2 protein family meet at this mitochondrial membrane system and decide about the fate of the cell. High intra-cellular oxidative stress levels trigger this cell death process and initiate permeabilization of the MOM and the release of cytochrome c. In recent years we have developed a realistic, MOM-like membrane system based on PC/PE/CL lipid mixed, an ideal system for elucidating the role of oxidized lipids on the regulation of mitochondria-mediated apoptosis. By using solid state NMR approaches in combination with neutron reflectometry approaches we could generate a comprehensive model of the dynamic and structural organization of these membranes under oxidative stress conditions. In particular we provided novel insight into the overall architecture behind the membrane's basic function, but also about its dynamics across the entire membrane using 13C MAS NMR and dynamic filters such as CP and INEPT.We observed that the MOM environment is severely altered structurally and dynamically in the presence of oxidized lipids (OxPls). To obtain a more comprehensive view about the overall organization across these membranes and changes due to oxidative stress and the presence of apoptosis regulating proteins of the Bcl-2 family we also employ neutron reflectometry (SURF at ISIS, UK). By this research we provide a basic understanding of the molecular mechanism by which OxPls are involved in regulation of apoptosis at the mitochondrial outer membrane and how apoptotic proteins such as Bax or its counterplayer Bcl-2 interact with them.