Smac/DIABLO is a mitochondrial protein that is released along with cytochrome c during apoptosis and activates cytochrome c/Apaf-1/caspase-9 pathway. Smac/DIABLO binds to IAPs (Inhibitor of Apoptosis Proteins) and neutralizes the inhibitory effect of IAPs. Analysis of the structural basis of Smac/DIABLO has revealed that the N-terminal amino acids are required for Smac/DIABLO to bind to IAPs and activation of caspases.