1.A.21.1.3
The mitochondrial apoptosis-inducing channel-forming protein, BAK. 3-D structures are known (2IMT_A).  Functions like a holin when expressed in bacteria (Pang et al. 2011).  Formation of the apoptotic pore involves a flexible C-terminal domain (Iyer et al. 2015). 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). BAK is a C-tail-anchored mitochondrial outer membrane protein (Setoguchi et al. 2006). BAK plays a role in peroxisomal permeability, similar to mitochondrial outer membrane permeabilization (Hosoi 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 herniates, carrying with it mitochondrial matrix components including the mitochondrial genome (McArthur et al. 2018). A high-resolution analysis of the conformational transition of pro-apoptotic Bak at the lipid membrane has been published (Sperl et al. 2021).