Chai J, Du C, Wu J W, Kyin S, Wang X, Shi Y
Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
Nature. 2000 Aug 24;406(6798):855-62. doi: 10.1038/35022514.
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.
凋亡（程序性细胞死亡）是后生动物发育和体内平衡中的一个重要过程，由半胱天冬酶执行。线粒体蛋白Smac/DIABLO通过消除凋亡抑制蛋白（IAPs）对半胱天冬酶的抑制作用，在凋亡过程中发挥关键功能。我们在此表明，Smac/DIABLO不仅促进procaspase-3的蛋白水解激活，还促进成熟caspase-3的酶活性，这两者都依赖于其与IAPs进行物理相互作用的能力。Smac/DIABLO在2.2埃分辨率下的晶体结构显示，它通过广泛的疏水界面形成同型二聚体。使这个二聚体界面失活的错义突变显著损害了Smac/DIABLO的功能。如同果蝇蛋白Reaper、Grim和Hid一样，Smac/DIABLO的氨基末端氨基酸对其功能不可或缺，并且从氨基末端衍生的一个七肽在体外促进procaspase-3的激活。这些结果为Smac/DIABLO激活凋亡建立了一个进化上保守的结构和生化基础。
