A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis
A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis
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DOI：
10.1038/35065125
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发表时间：
2001-03-01
期刊：
影响因子：
64.8
通讯作者：
Alnemri, ES
中科院分区：
文献类型：
--
作者：
Srinivasula, SM;Hegde, R;Alnemri, ES
X连锁凋亡相关蛋白（XIAP）与半胱天冬酶-9相互作用并抑制其活性（1-3），而Smac（也称为DIABLO）通过与XIAP相互作用缓解这种抑制（4-7）。在这里，我们表明，XIAP与活性caspase-9-Apaf-1全酶复合物通过结合到caspase-9的小亚基上的接头肽的氨基末端，其在天冬氨酸蛋白酶原-9的蛋白水解加工后暴露在Asp 315。支持这一观察结果的是，废除蛋白水解加工但不废除半胱天冬酶-9的催化活性的点突变，或接头肽的缺失，阻止了半胱天冬酶-9与XIAP的结合及其伴随的抑制。我们注意到胱天蛋白酶-9连接肽的N-末端四个残基与成熟Smac和果蝇蛋白Hid/Grim/Reaper中的N-末端四肽具有显著的同源性（8，9），从而定义了一类保守的IAP结合基序。与该发现一致，胱天蛋白酶-9连接肽和Smac与XIAP的BIR 3结构域的结合是互斥的，表明Smac通过破坏胱天蛋白酶-9的连接肽与BIR 3的相互作用来增强胱天蛋白酶-9活性。我们的研究揭示了一种机制，其中结合到BIR 3结构域的两个保守的肽，一个从Smac和其他一个从caspase-9，具有相反的影响caspase的活性和细胞凋亡。
X-linked inhibitor-of-apoptosis protein (XIAP) interacts with caspase-9 and inhibits its activity(1-3), whereas Smac (also known as DIABLO) relieves this inhibition through interaction with XIAP(4-7). Here we show that XIAP associates with the active caspase-9-Apaf-1 holoenzyme complex through binding to the amino terminus of the linker peptide on the small subunit of caspase-9, which becomes exposed after proteolytic processing of procaspase-9 at Asp 315. Supporting this observation, point mutations that abrogate the proteolytic processing but not the catalytic activity of caspase-9, or deletion of the linker peptide, prevented caspase-9 association with XIAP and its concomitant inhibition. We note that the N-terminal four residues of caspase-9 linker peptide share significant homology with the N-terminal tetra-peptide in mature Smac and in the Drosophila proteins Hid/Grim/Reaper(8,9), defining a conserved class of IAP-binding motifs. Consistent with this finding, binding of the caspase-9 linker peptide and Smac to the BIR3 domain of XIAP is mutually exclusive, suggesting that Smac potentiates caspase-9 activity by disrupting the interaction of the linker peptide of caspase-9 with BIR3. Our studies reveal a mechanism in which binding to the BIR3 domain by two conserved peptides, one from Smac and the other one from caspase-9, has opposing effects on caspase activity and apoptosis.