Blanchard H, Kodandapani L, Mittl P R, Marco S D, Krebs J F, Wu J C, Tomaselli K J, Grütter M G
Biochemisches Institut Universität Zürich Winterthurer Strasse 190, CH-8057, Zürich, Switzerland.
Structure. 1999 Sep 15;7(9):1125-33. doi: 10.1016/s0969-2126(99)80179-8.
In the initial stages of Fas-mediated apoptosis the cysteine protease caspase-8 is recruited to the cell receptor as a zymogen (procaspase-8) and is incorporated into the death-signalling complex. Procaspase-8 is subsequently activated leading to a cascade of proteolytic events, one of them being the activation of caspase-3, and ultimately resulting in cell destruction. Variations in the substrate specificity of different caspases have been reported.
We report here the crystal structure of a complex of the activated human caspase-8 (proteolytic domain) with the irreversible peptidic inhibitor Z-Glu-Val-Asp-dichloromethylketone at 2.8 A resolution. This is the first structure of a representative of the long prodomain initiator caspases and of the group III substrate specificity class. The overall protein architecture resembles the caspase-1 and caspase-3 folds, but shows distinct structural differences in regions forming the active site. In particular, differences observed in subsites S(3), S(4) and the loops involved in inhibitor interactions explain the preference of caspase-8 for substrates with the sequence (Leu/Val)-Glu-X-Asp.
The structural differences could be correlated with the observed substrate specificities of caspase-1, caspase-3 and caspase-8, as determined from kinetic experiments. This information will help us to understand the role of the various caspases in the propagation of the apoptotic signal. The information gained from this investigation should be useful for the design of specific inhibitors.
在Fas介导的细胞凋亡初始阶段，半胱氨酸蛋白酶caspase-8作为一种酶原（procaspase-8）被招募到细胞受体，并被纳入死亡信号复合物中。随后procaspase-8被激活，引发一系列蛋白水解事件，其中之一是caspase-3的激活，最终导致细胞破坏。据报道，不同caspase的底物特异性存在差异。
我们在此报告了活化的人caspase-8（蛋白水解结构域）与不可逆肽类抑制剂Z-Glu-Val-Asp-二氯甲基酮复合物的晶体结构，分辨率为2.8埃。这是长前结构域起始caspase代表以及III类底物特异性类别的首个结构。整体蛋白质结构类似于caspase-1和caspase-3的折叠，但在形成活性位点的区域显示出明显的结构差异。特别是，在S(3)、S(4)亚位点以及参与抑制剂相互作用的环中观察到的差异，解释了caspase-8对具有(Leu/Val)-Glu-X-Asp序列底物的偏好。
结构差异可能与从动力学实验确定的caspase-1、caspase-3和caspase-8的底物特异性相关。这些信息将有助于我们理解各种caspase在凋亡信号传导中的作用。从这项研究中获得的信息应该有助于设计特异性抑制剂。
