Mitochondrial Membranes Involved in Apoptosis - the Bcl-2 Proteins

Abstract

Removal of cells via programmed cell death (apoptosis) is an essential mechanism in life. Upon internal stress clearance of undesired cells is executed via intrinsic (mitochondrial) apoptosis, a pathway tightly controlled by the Bcl-2 protein family. Its pro- and anti-apoptotic members meet at the mitochondrial surface, more precisely at its outer membrane system, where they arbitrate a life or death (membrane permeabilization) decision. Failures cause pathological disorders including abnormal embryogenic development and cancer. However, how opposing Bcl-2 members meet and form a sophisticated regulative network there, is still poorly understood due to the lack of structural and functional information for these proteins acting at the the mitochondrial membraneous surface. To provide structural about this molecular regulation mechanism occurring at the mitochondrial outer membrane system, we apply solid-state/liquid NMR approaches together with neutron reflectometry on two representative Bcl-2 family members, namely the anti-apoptotic Bcl-2 protein itself which is an integral membrane protein, and its counterpart, the pro-apoptotic, membrane perforating Bax protein. i) Using MOM-like membranes doped with oxidized lipids to simulate apoptosis triggering oxidative stress, we investigate changes in the dynamic and structural organization of these membranes in the presence of Bax protein to identify the key structural elements which regulate Bax perforation activity in response to type and level of oxidative membrane damage. ii) The atomic structure of the Bcl-2 membrane protein is still undetermined, preventing a detailed mechanistic insight into its function, especially its loops as anti-apoptotic molecular switches. We are going to provide this information by combining liquid-state NMR on Bcl-2 in micelles with solid-state NMR on Bcl-2/lipid assemblies.