The Anti-apoptotic Mitochondrial Membrane Protein Bcl-2; An Achilles Heel Of Cancer Cells?

Abstract

Escape from programmed cell death, apoptosis, is one of the main hallmarks of cancer.. The anti-apoptotic protein Bcl-2 belongs to the Bcl-2 protein family, which function as a major gatekeeper in the mitochondrial pathway. Bcl-2 is found to a great extent in many breast cancers and is highly involved in the inherent resistance to anti-cancer drugs. This protein is mitochondrial membrane-associated and we will use NMR spectroscopy to provide structural information of the membrane-mediated mechanism underlying the action of Bcl-2 as a potent inhibitor of cell death.For this purpose we express currently the full length protein and carry out various preliminary studies of the membrane dependent behaviour of synthesized segments of the proteins by a range of biophysical methods ranging from CD (Circular Dichroism), ATR (Attenuated Total Reflection), Calorimetry to solid state NMR spectroscopy.At present, we study the impact of the unique BH4 domain of the pro-survival Bcl-2 protein on the mitochondrial membranes, since this interaction seems to be essential to block any apoptotic activation with its connected pore-formation and cytochrome c release. Our first results reveal that the BH4 domain requires cardiolipin to be able to convert into an α-helix conformation. In contact with neutral membranes, the peptide seems to aggregate on the surface. Bcl-2's counterplayer is Bax protein which upon activation tranlocates to the mitochondrial membrane. In this process the first helix localized at the N-terminus of Bax (Bax-α1) can act as an addressing sequence, which upon activation directs the protein from the cytosol towards the mitochondrial surface. Our biophysical approach provided insight into the molecular mechanism behind the recognition of the mitochondrial membrane system by the Bax-α1 sequence.