Ministry of Education Protein Science Laboratory, Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, China.
Nat Commun. 2011 Aug 2;2:408. doi: 10.1038/ncomms1418.
The Drosophila inhibitor of apoptosis protein DIAP1 exists in an auto-inhibited conformation, unable to suppress the effector caspase drICE. Auto-inhibition is disabled by caspase-mediated cleavage of DIAP1 after Asp20. The cleaved DIAP1 binds to mature drICE, inhibits its protease activity, and, presumably, also targets drICE for ubiquitylation. DIAP1-mediated suppression of drICE is effectively antagonized by the pro-apoptotic proteins Reaper, Hid, and Grim (RHG). Despite rigorous effort, the molecular mechanisms behind these observations are enigmatic. Here we report a 2.4 Å crystal structure of uncleaved DIAP1-BIR1, which reveals how the amino-terminal sequences recognize a conserved surface groove in BIR1 to achieve auto-inhibition, and a 3.5 Å crystal structure of active drICE bound to cleaved DIAP1-BIR1, which provides a structural explanation to DIAP1-mediated inhibition of drICE. These structures and associated biochemical analyses, together with published reports, define the molecular determinants that govern the interplay among DIAP1, drICE and the RHG proteins.
果蝇凋亡抑制蛋白 DIAP1 以自身抑制构象存在，无法抑制效应半胱天冬酶 drICE。Caspase 介导的 DIAP1 在 Asp20 后切割可使自身抑制失活。切割后的 DIAP1 与成熟的 drICE 结合，抑制其蛋白酶活性，并可能将 drICE 作为泛素化的靶标。凋亡蛋白抑制物 1（DIAP1）介导的对 drICE 的抑制作用被促凋亡蛋白 Reaper、Hid 和 Grim（RHG）有效拮抗。尽管进行了严格的努力，但这些观察结果背后的分子机制仍然是神秘的。在这里，我们报告了未切割的 DIAP1-BIR1 的 2.4 Å 晶体结构，该结构揭示了氨基末端序列如何识别 BIR1 中的保守表面凹槽以实现自身抑制，以及与切割的 DIAP1-BIR1 结合的活性 drICE 的 3.5 Å 晶体结构，该结构为 DIAP1 介导的 drICE 抑制提供了结构解释。这些结构和相关的生化分析，以及已发表的报告，定义了控制 DIAP1、drICE 和 RHG 蛋白相互作用的分子决定因素。
