Structural and biochemical basis of apoptotic activation by Smac/DIABLO.
Apoptosis (programmed cell death), an essential process in the development and homeostasis of metazoans, is carried out by caspases. The mitochondrial protein Smac/DIABLO performs a critical function in apoptosis by eliminating the inhibitory effect of IAPs (inhibitor of apoptosis proteins) on caspases. Here we show that Smac/DIABLO promotes not only the proteolytic activation of procaspase-3 but also the enzymatic activity of mature caspase-3, both of which depend upon its ability to interact physically with IAPs. The crystal structure of Smac/DIABLO at 2.2 A resolution reveals that it homodimerizes through an extensive hydrophobic interface. Missense mutations inactivating this dimeric interface significantly compromise the function of Smac/DIABLO. As in the Drosophila proteins Reaper, Grim and Hid, the amino-terminal amino acids of Smac/DIABLO are indispensable for its function, and a seven-residue peptide derived from the amino terminus promotes procaspase-3 activation in vitro. These results establish an evolutionarily conserved structural and biochemical basis for the activation of apoptosis by Smac/DIABLO.
Chai
J
J
Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
Du
C
C
Wu
J W
JW
Kyin
S
S
Wang
X
X
Shi
Y
Y
D000595:Amino Acid Sequence; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D018360:Crystallography, X-Ray; D019281:Dimerization; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D004926:Escherichia coli; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D008956:Models, Chemical; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C412403:DIABLO protein, human; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases