The mitochondrial apoptosis-inducing channel-forming protein, BAX.  The C-terminal helix mediates membrane binding and pore formation (Garg et al. 2012). BAX pores are large enough to allow cytochrome c release and it activates the mitochondrial permeabilty transition pore; both play a role in programmed cell death, but the latter is quantitatively more important (Gómez-Crisóstomo et al. 2013). Bax functions like a holin when expressed in bacteria (Pang et al. 2011).  Bax (and likely Bak) dimers assemble into oligomers with an even number of molecules that fully or partially delineate pores of different sizes to permeabilize the mitochondrial outer membrane (MOM) during apoptosis (Cosentino and García-Sáez 2016). The membrane domain of Bax interacts with other members of the Bcl-2 family to form hetero-oligomers (Andreu-Fernández et al. 2017).  Uren et al. 2017 reviewed how clusters of dimers and their lipid-mediated interactions provide a molecular explanation for the heterogeneous assemblies of Bak and Bax observed during apoptosis. After BAK/BAX activation and cytochrome c loss, the mitochondrial network breaks down, and large BAK/BAX pores appear in the outer membrane. These macropores allow the inner membrane an outlet through which it herniated, carrying with it mitochondrial matrix components including the mitochondrial genome (McArthur et al. 2018). The core/dimerization domain of Bax and Bak is water exposed with only helices 4 and 5 in membrane contact, whereas the piercing/latch domain is in peripheral membrane contact, with helix 9 being transmembrane (Bleicken et al. 2018). The mechanism of the membrane disruption and pore-formation by the BAX C-terminal TMS has been investigated (Jiang and Zhang 2019).  Bax membrane permeabilization results from oligomerization of transmembrane monomers (Annis et al. 2005). Bax localization and apoptotic activity are conformationally controled by Pro168 (Schinzel et al. 2004).