Department of Biology and Genetics, Stanford University, Stanford, CA 94305, USA.
Department of Biological Science, Seoul National University, Seoul, South Korea.
Cell. 2019 Apr 18;177(3):751-765.e15. doi: 10.1016/j.cell.2019.03.012. Epub 2019 Apr 4.
Maintaining proteostasis in eukaryotic protein folding involves cooperation of distinct chaperone systems. To understand how the essential ring-shaped chaperonin TRiC/CCT cooperates with the chaperone prefoldin/GIMc (PFD), we integrate cryoelectron microscopy (cryo-EM), crosslinking-mass-spectrometry and biochemical and cellular approaches to elucidate the structural and functional interplay between TRiC/CCT and PFD. We find these hetero-oligomeric chaperones associate in a defined architecture, through a conserved interface of electrostatic contacts that serves as a pivot point for a TRiC-PFD conformational cycle. PFD alternates between an open "latched" conformation and a closed "engaged" conformation that aligns the PFD-TRiC substrate binding chambers. PFD can act after TRiC bound its substrates to enhance the rate and yield of the folding reaction, suppressing non-productive reaction cycles. Disrupting the TRiC-PFD interaction in vivo is strongly deleterious, leading to accumulation of amyloid aggregates. The supra-chaperone assembly formed by PFD and TRiC is essential to prevent toxic conformations and ensure effective cellular proteostasis.
真核蛋白折叠过程中的蛋白稳态维持需要不同的伴侣系统的协作。为了了解基本的环形伴侣蛋白 TRiC/CCT 如何与伴侣前体蛋白/GIMc（PFD）相互作用，我们综合运用了冷冻电镜（cryo-EM）、交联质谱和生化及细胞方法来阐明 TRiC/CCT 和 PFD 之间的结构和功能相互作用。我们发现这些异源寡聚伴侣蛋白以一种确定的结构方式结合，通过静电接触的保守界面作为 TRiC-PFD 构象循环的枢轴点。PFD 在打开的“锁定”构象和关闭的“结合”构象之间交替，使 PFD-TRiC 底物结合腔对齐。PFD 可以在 TRiC 结合其底物后发挥作用，以提高折叠反应的速度和产率，抑制非生产性反应循环。在体内破坏 TRiC-PFD 相互作用会导致严重的毒性，导致淀粉样聚集物的积累。由 PFD 和 TRiC 形成的超伴侣组装对于防止有毒构象和确保有效的细胞蛋白稳态至关重要。
