Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
Cryo-EM Facility, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
Cell. 2018 Sep 6;174(6):1507-1521.e16. doi: 10.1016/j.cell.2018.07.006. Epub 2018 Aug 9.
The hetero-oligomeric chaperonin of eukarya, TRiC, is required to fold the cytoskeletal protein actin. The simpler bacterial chaperonin system, GroEL/GroES, is unable to mediate actin folding. Here, we use spectroscopic and structural techniques to determine how TRiC promotes the conformational progression of actin to the native state. We find that actin fails to fold spontaneously even in the absence of aggregation but populates a kinetically trapped, conformationally dynamic state. Binding of this frustrated intermediate to TRiC specifies an extended topology of actin with native-like secondary structure. In contrast, GroEL stabilizes bound actin in an unfolded state. ATP binding to TRiC effects an asymmetric conformational change in the chaperonin ring. This step induces the partial release of actin, priming it for folding upon complete release into the chaperonin cavity, mediated by ATP hydrolysis. Our results reveal how the unique features of TRiC direct the folding pathway of an obligate eukaryotic substrate.
真核生物的异源寡聚伴侣蛋白 TRiC 对于细胞骨架蛋白肌动蛋白的折叠是必需的。更为简单的细菌伴侣蛋白体系 GroEL/GroES 则无法介导肌动蛋白的折叠。在这里，我们使用光谱学和结构技术来确定 TRiC 如何促进肌动蛋白向天然状态的构象进展。我们发现，即使在没有聚集的情况下，肌动蛋白也无法自发折叠，但会进入一种动力学捕获的构象动态状态。这种受阻的中间产物与 TRiC 的结合指定了肌动蛋白的扩展拓扑结构，具有类似天然的二级结构。相比之下，GroEL 将结合的肌动蛋白稳定在未折叠状态。ATP 结合到 TRiC 上会引起伴侣蛋白环的不对称构象变化。这一步骤诱导肌动蛋白的部分释放，为其在完全释放到伴侣蛋白腔中后进行折叠做好准备，这一过程由 ATP 水解介导。我们的结果揭示了 TRiC 如何指导必需的真核底物的折叠途径。
