State Key Laboratory of Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, China.
State Key Laboratory of Molecular Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai, China; Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China.
Cell Res. 2023 Nov;33(11):851-866. doi: 10.1038/s41422-023-00859-3. Epub 2023 Aug 14.
Ultra-stable fibrous structure is a hallmark of amyloids. In contrast to canonical disease-related amyloids, emerging research indicates that a significant number of cellular amyloids, termed 'functional amyloids', contribute to signal transduction as temporal signaling hubs in humans. However, it is unclear how these functional amyloids are effectively disassembled to terminate signal transduction. RHIM motif-containing amyloids, the largest functional amyloid family discovered thus far, play an important role in mediating necroptosis signal transduction in mammalian cells. Here, we identify heat shock protein family A member 8 (HSPA8) as a new type of enzyme - which we name as 'amyloidase' - that directly disassembles RHIM-amyloids to inhibit necroptosis signaling in cells and mice. Different from its role in chaperone-mediated autophagy where it selects substrates containing a KFERQ-like motif, HSPA8 specifically recognizes RHIM-containing proteins through a hydrophobic hexapeptide motif N(X)φ(X). The SBD domain of HSPA8 interacts with RHIM-containing proteins, preventing proximate RHIM monomers from stacking into functional fibrils; furthermore, with the NBD domain supplying energy via ATP hydrolysis, HSPA8 breaks down pre-formed RHIM-amyloids into non-functional monomers. Notably, HSPA8's amyloidase activity in disassembling functional RHIM-amyloids does not require its co-chaperone system. Using this amyloidase activity, HSPA8 reverses the initiator RHIM-amyloids (formed by RIP1, ZBP1, and TRIF) to prevent necroptosis initiation, and reverses RIP3-amyloid to prevent necroptosis execution, thus eliminating multi-level RHIM-amyloids to effectively prevent spontaneous necroptosis activation. The discovery that HSPA8 acts as an amyloidase dismantling functional amyloids provides a fundamental understanding of the reversibility nature of functional amyloids, a property distinguishing them from disease-related amyloids that are unbreakable in vivo.
超稳定的纤维结构是淀粉样蛋白的标志。与典型的与疾病相关的淀粉样蛋白不同，新兴的研究表明，大量的细胞淀粉样蛋白，称为“功能淀粉样蛋白”，作为人类中临时信号枢纽参与信号转导。然而，目前尚不清楚这些功能淀粉样蛋白如何有效地被拆卸以终止信号转导。迄今为止发现的最大的功能淀粉样蛋白家族 RHIM 基序包含的淀粉样蛋白，在调节哺乳动物细胞中的坏死性凋亡信号转导中发挥着重要作用。在这里，我们鉴定热休克蛋白家族 A 成员 8（HSPA8）为一种新型的酶 - 我们将其命名为“淀粉样蛋白酶” - 它可以直接拆卸 RHIM-淀粉样蛋白，从而抑制细胞和小鼠中的坏死性凋亡信号。与它在伴侣介导的自噬中的作用不同，在自噬中它选择含有 KFERQ 样基序的底物，HSPA8 特异性地通过疏水六肽基序 N(X)φ(X)识别含有 RHIM 的蛋白质。HSPA8 的 SBD 结构域与含有 RHIM 的蛋白质相互作用，防止相邻的 RHIM 单体堆叠成功能性纤维；此外，通过 NBD 结构域利用 ATP 水解提供能量，HSPA8 将预先形成的 RHIM-淀粉样蛋白分解成无功能的单体。值得注意的是，HSPA8 在拆卸功能性 RHIM-淀粉样蛋白中的淀粉样蛋白酶活性不需要其伴侣蛋白系统。利用这种淀粉样蛋白酶活性，HSPA8 将起始 RHIM-淀粉样蛋白（由 RIP1、ZBP1 和 TRIF 形成）逆转，以防止坏死性凋亡的起始，并将 RIP3-淀粉样蛋白逆转，以防止坏死性凋亡的执行，从而消除多层次的 RHIM-淀粉样蛋白，有效地防止自发性坏死性凋亡的激活。HSPA8 作为一种淀粉样蛋白酶来拆卸功能淀粉样蛋白的发现，为功能淀粉样蛋白的可逆性本质提供了基本的理解，这一特性将它们与体内不可破坏的与疾病相关的淀粉样蛋白区分开来。
