The inhibitor of apoptosis (IAP) proteins are major regulators of apoptosis that bind to and inhibit caspases-3,-7, and/or-9.Overexpression of IAP proteins has been demonstrated to confer protection against a variety of proapoptotic stimuli, including chemotherapies, and is a marker for poor prognosis in a variety of solid tumors and hematologic malignancies.All IAP proteins contain one to three copies of the baculoviral IAP repeat (BIR) domain, zinc-binding domains of about 80 amino acids, that are necessary for their interactions with a number of cytosolic target proteins, including activated caspases-3,-7, and/or-9.Antagonism of the IAP protein-mediated inhibition of these caspases is required for caspase-dependent cell death, and can be achieved by the mitochondrial protein second mitochondria-derived activator of caspases/direct IAP-binding protein with low pI (Smac/DIABLO), which is released into the cytoplasm in response to pro-apoptotic stimuli.