Structural and biochemical basis of apoptotic activation by Smac/DIABLO

Abstract

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 Å 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.

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Figure 1: Schematic representation of Smac structure.
Figure 2: Specificity at the dimeric interface.
Figure 3: Functional significance of the dimeric interface in Smac.
Figure 4: Functional significance of the N terminus of Smac.
Figure 5: N-terminal peptides of Smac directly promote the activation of procaspase-3.
Figure 6: Model of Smac function.

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Acknowledgements

We thank D. Vaux for providing XIAP cDNA; E. Alnemri for providing caspase-3 expression vector; F. Hughson for critically reading the manuscript; and N. Hunt for secretarial assistance. This work was supported by start-up funds from Princeton University (to Y.S.) and Howard Hughes Medical Institute (to X.W.). Y.S. is a Searle Scholar and a Rita Allen Scholar.

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Correspondence to Yigong Shi.

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Chai, J., Du, C., Wu, JW. et al. Structural and biochemical basis of apoptotic activation by Smac/DIABLO . Nature 406, 855–862 (2000). https://doi.org/10.1038/35022514

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