Observation of real-time interactions of Bcl-2 family members during apoptosis

Apoptosis is a physiological process of cell death resulting from an intricate cascade of sequential protein-protein interactions. Using donor and acceptor mutant GFP fusion constructs, we have monitored the interaction between specific pro- and anti-apoptotic members of the Bcl-2 family with each other as well as proteins located in the outer mitochondrial membrane, as current hypotheses regarding apoptosis suggest that interaction of Bcl-2 family members with each other, or with other mitochondrial membrane proteins, regulates apoptosis. Our data indicate that specific interactions between pro- and anti-apoptotic Bcl-2 family members do occur in situ in the mitochondrial membrane, are altered during apoptosis and regulate cellular sensitivity to apoptosis. These findings are the first to demonstrate real time protein-protein interactions in situ at the level of individual mitochondria.