Chai J, Wu Q, Shiozaki E, Srinivasula S M, Alnemri E S, Shi Y
Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ 08544, USA.
Cell. 2001 Nov 2;107(3):399-407. doi: 10.1016/s0092-8674(01)00544-x.
Apoptosis is primarily executed by active caspases, which are derived from the inactive procaspase zymogens through proteolytic cleavage. Here we report the crystal structures of a caspase zymogen, procaspase-7, and an active caspase-7 without any bound inhibitors. Compared to the inhibitor-bound caspase-7, procaspase-7 zymogen exhibits significant structural differences surrounding the catalytic cleft, which precludes the formation of a productive conformation. Proteolytic cleavage between the large and small subunits allows rearrangement of essential loops in the active site, priming active caspase-7 for inhibitor/substrate binding. Strikingly, binding by inhibitors causes a 180 degrees flipping of the N terminus in the small subunit, which interacts with and stabilizes the catalytic cleft. These analyses reveal the structural mechanisms of caspase activation and demonstrate that the inhibitor/substrate binding is a process of induced fit.
细胞凋亡主要由活性半胱天冬酶执行，这些活性半胱天冬酶是通过蛋白水解切割从不活性的半胱天冬酶原衍生而来。在此，我们报告了一种半胱天冬酶原——半胱天冬酶-7以及没有任何结合抑制剂的活性半胱天冬酶-7的晶体结构。与结合抑制剂的半胱天冬酶-7相比，半胱天冬酶-7原酶在催化裂隙周围表现出显著的结构差异，这阻止了有效构象的形成。大小亚基之间的蛋白水解切割允许活性位点中关键环的重排，使活性半胱天冬酶-7能够结合抑制剂/底物。引人注目的是，抑制剂的结合导致小亚基中N末端180度翻转，该N末端与催化裂隙相互作用并使其稳定。这些分析揭示了半胱天冬酶激活的结构机制，并证明抑制剂/底物结合是一个诱导契合的过程。
