Insight into Bcl-2 proteins' functioning at mitochondrial membrane level

Programmed cell death (apoptosis) is essential in life. In its intrinsic apoptotic pathway opposing members of the B-cell lymphoma 2 (Bcl-2) protein family control the permeability of the mitochondrial outer membrane (MOM) and the release of apoptotic factors such as cytochrome c. Any misregulation of this process can cause disorders most prominently cancer, where often upregulation of cell protecting (anti-apoptotic) Bcl-2 members such as the Bcl-2 membrane protein itself plays a notorious role by blocking MOM perforation by - often drug induced - apoptotic proteins such as Bax which would cause cancer cell death normally. Here, we apply neutron reflectometry (NR) on supported lipid bilayers which mimic MOM environment and solid state/liquid state NMR spectroscopy to unravel the molecular basis driving opposing proteins to interact with each other at the MOM; a mechanism which is not really understood yet due to lack of high-resolution structural insight. Based on our central hypothesis that Bcl-2 drives its cell-protecting function at a membrane-embedded location as revealed by NR (1), we focus i) to determine the structure of human Bcl-2 protein in its membrane setting by combining solution and solid-state NMR; ii) use NR to study the kinetics and lipid/protein pore assemblied upon binding of Bax to mitochondrial membranes and its membrane destroying activities there; and iii) unravel the nature of direct interaction between Bcl-2 and Bax to neutralize each other. Knowledge generated here, will be indispensable in understanding the regulative function of the Bcl-2 family at mitochondrial membranes. 1. A. Ul Mushtaq, J. Åden, L.A. Clifton, H. Wacklin-Knecht, M. Campana, A.P.G. Dingeldein, C. Persson, T. Sparrman, G. Gröbner. Neutron reflectometry and NMR spectroscopy of full length Bcl-2 protein reveal its membrane localization and conformation. Communications Biology 4 (2021) 507.