Cell death in animals mainly proceeds through the programmed process of apoptosis. In vertebrates, this usually occurs by means of a pathway involving the mitochondrion, a cellular organelle1. Following damaging cellular stress, the outer mitochondrial membrane becomes permeable, and factors are released into the cytoplasm that precipitate apoptosis. The pro-apoptotic effector proteins of the BCL-2 family - BAK and BAX - are responsible for permeabilizing the membrane, yet there is little structural information on the main protein-protein interactions necessary to promote this mitochondrial event. On page 1076 of this issue, Walensky, Tjandra and colleagues2 present an intriguing structural analysis of the interactions between BAX and one of its activators, revealing an unsuspected binding site.
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