A single BIR domain of XIAP sufficient for inhibiting caspases
A single BIR domain of XIAP sufficient for inhibiting caspases
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DOI：
10.1074/jbc.273.14.7787
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发表时间：
1998-04-03
影响因子：
4.8
通讯作者：
Reed, JC
中科院分区：
文献类型：
--
作者：
Takahashi, R;Deveraux, Q;Reed, JC
凋亡抑制蛋白（inhibitor of apoptosis proteins，IAPs）是一个进化上保守的同源蛋白家族，能抑制多种刺激诱导的细胞凋亡。一些IAP家族蛋白，包括XIAP、cIAP-1和cIAP-2，可以结合并直接抑制选定的半胱天冬酶，一组细胞内细胞死亡蛋白酶。这些半胱天冬酶抑制IAP家族蛋白都含有三个串联的BIR结构域，随后是RING锌指结构域。为了确定XIAP抑制caspase的结构基础，我们分析了IAP家族蛋白的各种片段对体外caspase活性和完整细胞中凋亡抑制的影响。XIAP的RING结构域不能抑制重组半胱天冬酶-3或-7的活性，而XIAP的一个片段包含三个串联的BIR结构域，在体外有效地抑制这些半胱天冬酶，并阻断Fas（CD 95）诱导的细胞凋亡时，在细胞中表达。对XIAP蛋白的进一步分析表明，只有三个BIR结构域中的第二个（BIR 2）能够结合和抑制这些半胱天冬酶。BIR 2介导的caspase-3和caspase-7抑制的表观抑制常数（Ki）为2-5 nM，表明该单一BIR结构域具有有效的抗caspase活性。BIR 2在细胞中的表达主要也部分抑制Fas诱导的细胞凋亡，并阻断细胞溶质提取物中细胞色素c诱导的caspase-9加工，而BIR 1和BIR 3则没有。这些发现将BIR 2鉴定为XIAP的最小半胱天冬酶抑制结构域，并表明单个BIR结构域足以结合和抑制半胱天冬酶。
The inhibitor of apoptosis proteins (IAPs) constitute an evolutionarily conserved family of homologous proteins that suppress apoptosis induced by multiple stimuli. Some IAP family proteins, including XIAP, cIAP-1, and cIAP-2, can bind and directly inhibit selected caspases, a group of intracellular cell death proteases. These caspase-inhibiting IAP family proteins all contain three tandem BIR domains followed by a RING zinc finger domain. To determine the structural basis for caspase inhibition by XIAP, we analyzed the effects of various fragments of this IAP family protein on caspase activity in vitro and on apoptosis suppression in intact cells. The RING domain of XIAP failed to inhibit the activity of recombinant caspases-3 or -7, whereas a fragment of XIAP encompassing the three tandem BIR domains potently inhibited these caspases in vitro and blocked Fas (CD95)-induced apoptosis when expressed in cells. Further dissection of the XIAP protein demonstrated that only the second of the three BIR domains (BIR2) was capable of binding and inhibiting these caspases. The apparent inhibition constants (K-i) for BIR2-mediated inhibition of caspases-3 and -7 were 2-5 nM, indicating that this single BIR domain possesses potent anti caspase activity, Expression of the BIR2 do main in cells also partially suppressed Fas-induced apoptosis and blocked cytochrome c-induced processing of caspase-9 in cytosolic extracts, whereas BIR1 and BIR3 did not. These findings identify BIR2 as the minimal caspase-inhibitory domain of XIAP and indicate that a single BIR domain can be sufficient for binding and inhibiting caspases.