BAX and cancer: A thorough understanding of BH3-only proteins is crucial for the development of cancer therapeutics such as the new class of anti-cancer molecules called BH3 mimetics that are showing significant promise in clinical trials.12, 13 The binding of BH3-only proteins to prosurvival proteins has been well-characterized and revealed significant preferences for engaging different members.6, 8, 9 How BH3-only proteins bind and activate Bak and Bax remains less understood for several reasons.