The Structural Basis for Bax-mediated Membrane Permeabilization

Apoptosis is a form of controlled cell death, which is a vital process to maintain healthy and functional cells. There are two main apoptotic pathways: the intrinsic pathway and the extrinsic pathway. Disruption of the apoptosis mechanism can lead to several diseases, such as different types of cancer and neurodegenerative diseases. Bax is a protein that is vital in the intrinsic pathway. When the intrinsic pathway is triggered, Bax activates and translocates from the cytosol to the mitochondrial outer membrane. It starts to oligomerize and forms a pore, which leads to mitochondrial outer membrane permeabilization. This results in the release of mitochondrial proteins into the cytosol, which eventually leads to cell death. Endophilin B1, a membrane-remodeling protein implicated in apoptosis, has been proposed to cooperate with Bax during mitochondrial outer membrane permeabilization, although its exact role remains unclear. The aim of this project is to investigate the mechanisms of Bax, the potential cooperative role of endophilin B1 in this process, and how different apoptotic stimuli can induce early apoptosis in mammalian cells. In in vitro studies using artificial liposomes, Bax was shown to form pores, and the degree of cardiolipin saturation rather than its concentration was found to enhance the Bax-mediated permeabilization. Endophilin B1 appeared to hinder Bax from performing mitochondrial outer membrane permeabilization rather than promoting under the tested conditions, though this may be due to experimental factors such as excess Endophilin B1 concentration. Further investigation is needed to clarify this interaction. Early apoptosis is induced in HeLa cells when incubated with 10μM embelin and 20μM caspase inhibitor for 2 hours, allowing visualization of Bax mitochondrial recruitment while preventing cell detachment. This condition can be used for future high-resolution imaging to explore protein–protein interactions at the mitochondria.