Untangling aggregates one step at a time Conserved AAA+ protein complexes exploit adenosine triphosphate hydrolysis to unfold and disaggregate their substrates in response to cell stress, but exactly how they do this has been unclear. Gates et al. determined high-resolution cryo-electron microscopy structures of the Hsp104 disaggregase bound to an unfolded polypeptide substrate in its channel. The structures reveal substrate interactions and two different translocation states. Hsp104 undergoes conformational changes that drive movement along the substrate by two-amino-acid steps. These states help explain how this molecular machine can solubilize protein aggregates and amyloids. Science, this issue p. 273 Cryo–electron microscopy structures of an AAA+ machine reveal details of the mechanism used for substrate protein disaggregation. Hsp100 polypeptide translocases are conserved members of the AAA+ family (adenosine triphosphatases associated with diverse cellular activities) that maintain proteostasis by unfolding aberrant and toxic proteins for refolding or proteolytic degradation. The Hsp104 disaggregase from Saccharomyces cerevisiae solubilizes stress-induced amorphous aggregates and amyloids. The structural basis for substrate recognition and translocation is unknown. Using a model substrate (casein), we report cryo–electron microscopy structures at near-atomic resolution of Hsp104 in different translocation states. Substrate interactions are mediated by conserved, pore-loop tyrosines that contact an 80-angstrom-long unfolded polypeptide along the axial channel. Two protomers undergo a ratchet-like conformational change that advances pore loop–substrate interactions by two amino acids. These changes are coupled to activation of specific nucleotide hydrolysis sites and, when transmitted around the hexamer, reveal a processive rotary translocation mechanism and substrate-responsive flexibility during Hsp104-catalyzed disaggregation.

中文翻译：

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AAA+解聚酶Hsp104的棘轮样多肽易位机制

一次一步解开聚集体 保守的 AAA+ 蛋白质复合物利用三磷酸腺苷水解来展开和分解其底物以响应细胞压力，但具体如何做到这一点尚不清楚。盖茨等人。确定了 Hsp104 解聚酶的高分辨率冷冻电子显微镜结构，该酶与其通道中未折叠的多肽底物结合。这些结构揭示了底物相互作用和两种不同的易位状态。Hsp104 发生构象变化，通过两个氨基酸的步骤驱动沿底物的运动。这些状态有助于解释这种分子机器如何溶解蛋白质聚集体和淀粉样蛋白。科学，这个问题 p。273 AAA+ 机器的冷冻电子显微镜结构揭示了用于底物蛋白质分解的机制的详细信息。Hsp100 多肽转位酶是 AAA+ 家族（与多种细胞活动相关的三磷酸腺苷酶）的保守成员，它们通过展开异常和有毒蛋白质以进行重折叠或蛋白水解降解来维持蛋白质稳态。来自酿酒酵母的 Hsp104 解聚酶可溶解应激诱导的无定形聚集体和淀粉样蛋白。底物识别和易位的结构基础尚不清楚。使用模型底物（酪蛋白），我们报告了不同易位状态下 Hsp104 近原子分辨率的低温电子显微镜结构。底物相互作用由保守的孔环酪氨酸介导，酪氨酸沿轴向通道接触 80 埃长的未折叠多肽。两个原体经历棘轮状构象变化，通过两个氨基酸促进孔环-底物相互作用。这些变化与特定核苷酸水解位点的激活有关，并且当围绕六聚体传播时，揭示了 Hsp104 催化解聚过程中的进行性旋转易位机制和底物响应灵活性。