Second Mitochondria-derived Activator of Caspases promotes apoptosis by activating caspases in the cytochrome c/Apaf-1/caspase-9 pathway, and by opposing the inhibitory activity of inhibitor of apoptosis proteins (XIAP-BIR3). The protein assumes an elongated three-helix bundle structure, and forms a dimer in solution [1].

1: Structural basis of IAP recognition by Smac/DIABLO. Wu G, Chai J, Suber TL, Wu JW, Du C, Wang X, Shi Y; Nature. 2000;408:1008-1012. PMID:11140638