Ministry of Education Protein Science Laboratory, Tsinghua-Peking Joint Center for Life Sciences, Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China.
Cell Rep. 2013 Oct 17;5(1):70-8. doi: 10.1016/j.celrep.2013.08.044. Epub 2013 Oct 3.
RIP3 is an essential upstream kinase in necroptosis. The pseudokinase MLKL functions as a substrate of RIP3 to mediate downstream signaling. The molecular mechanism by which RIP3 recognizes and phosphorylates MLKL remains unknown. Here, we report the crystal structures of the mouse RIP3 kinase domain, the MLKL kinase-like domain, and a binary complex between the two. Both RIP3 and MLKL adopt the canonical kinase fold. Free RIP3 exists in an active conformation, whereas MLKL-bound RIP3 is stabilized by AMP-PNP to adopt an inactive conformation. The formation of the RIP3-MLKL complex, involving their respective N- and C-lobes, is accompanied by pronounced conformational changes of the αC helix and activation loop in RIP3 and the corresponding structural elements in MLKL. RIP3-mediated MLKL phosphorylation, though important for downstream signaling, is dispensable for stable complex formation between RIP3 and MLKL. Our study serves as a framework for mechanistic understanding of RIP3-mediated necroptotic signaling.
RIP3 是 necroptosis 中的必需上游激酶。假激酶 MLKL 作为 RIP3 的底物发挥作用，介导下游信号转导。RIP3 识别和磷酸化 MLKL 的分子机制尚不清楚。在这里，我们报告了鼠 RIP3 激酶结构域、MLKL 激酶样结构域以及两者之间二元复合物的晶体结构。RIP3 和 MLKL 均采用典型的激酶折叠。游离的 RIP3 处于活性构象，而与 MLKL 结合的 RIP3 被 AMP-PNP 稳定，从而采用无活性构象。RIP3-MLKL 复合物的形成涉及它们各自的 N-和 C-结构域，伴随着 RIP3 中的 αC 螺旋和激活环以及 MLKL 中相应结构元件的显著构象变化。虽然 RIP3 介导的 MLKL 磷酸化对于下游信号转导很重要，但对于 RIP3 和 MLKL 之间稳定复合物的形成是可有可无的。我们的研究为 RIP3 介导的 necroptotic 信号转导的机制理解提供了一个框架。
