(D) Structure of human BAK (PDB 2IMS) with the hydrophobic binding groove comprising α-helices 3-5 highlighted in blue. The ubiquitination site, K113, (red) resides in the binding groove. A modelled transmembrane anchor (α9) and the C-terminal K210 localised to the inter-membrane space is based on evidence that the BAK transmembrane anchor spans the mitochondrial outer membrane (Iyer et al CDD, 2014). The orientation of the soluble portion (α-helices 1-8) of BAK with respect to the mitochondrial outer membrane is hypothetical. 