D BAK-6H oligomerisation on liposomes involves its BH3 domain. Liposomes were incubated with BAK-6H (150 nM) together with cBID (90 nM). Antibody recognising the BAK BH3 domain (4B5) or α1-α2 loop (7D10), as shown on the structure of BAK (PDB:2IMS), were added (2.4 μg/μl) either prior to (pre) or after (post) incubation with cBID for 60 mins. BAK:Ab complex is indicated (arrowhead). 7D10 which recognises the activated form of mBAK (Iyer et al., 2016), bound to and gel-shifted BAK when added either before or after activation with cBID. In contrast, 4B5 failed to appreciably gel-shift inactive BAK (lanes 3 and 5) or BAK that was already activated (lane 6), but gel-shifted BAK when present during cBID activation (lane 4). Liposome permeabilisation was assessed after 20 min incubation with cBID (90 nM), BAK-6H (150 nM) and antibodies 4B5 (2.5 μg) or 7D10 (2.5 μg). Data is presented as mean of 2 independent experiments with percentage release relative to detergent-lysed liposomes at a timepoint when permeabilisation with BAK and cBid was approximately 50% of detergent-lysis maximum. 