The Bcl2 family proteins regulate and mediate the mitochondrial outer membrane permeabilization, a crucial event in the mitochondrial pathway of apoptosis in vertebrates.
The regulation of apoptosis is governed largely by interactions between the pro-survival and pro-death members of the Bcl2 protein family.
Some members of this family (e.g., Bax, Bak, and Bid: pro-apoptotic protines) promote apoptosis, while others such as BCL2, BCL2L1, BCL2L2 (anti-apoptotic protines)work against programmed cell death.
The BCL2 family proteins are characterized by regions of specific sequence homology named as BCL2 homology (BH) motifs that number from 1 to 4 and are critical for function.
Especially a helical BH3 motif of pro-apoptotic proteins occupy and form strong interactions with hydrophobic groove of anti-apoptotic BCL2 family proteins which leads to the activation of the essential death mediators Bax and Bak, thereby committing cells to apoptosis: