近日，德国马克斯·普朗克生物物理研究所Martin Beck等合作发现，原位分析揭示了TRiC的活性周期以及PDCD5作为开放状态下的辅助因子。这一研究成果于2024年12月11日发表在国际顶尖学术期刊《自然》上。

据悉，分子伴侣素(TRiC；也被称为含有TCP-1、CCT的伴侣蛋白）是ATP驱动的蛋白质折叠机器，对维持细胞稳态至关重要。其功能障碍与癌症和神经退行性疾病有关。尽管它很重要，但TRiC如何在细胞中起作用仍不清楚。

本文使用冷冻电子断层成像技术在人类细胞中，对分子伴侣TRiC的结构、构象动态和空间组织进行了分析。研究人员解析了TRiC的不同状态，包括开放状态、闭合状态、底物结合状态以及与前折叠蛋白关联的状态，并在原位重建了其功能周期。底物结合的开放状态和对称闭合状态的TRiC同样丰富。包含底物的闭合TRiC形成独特的簇，这表明了空间组织的模式。

翻译抑制并没有根本改变功能周期中间体的分布，但减少了所有状态的底物结合以及簇的形成。从细胞内结构中，研究人员发现，程序性细胞死亡蛋白5（PDCD5）作为一个相互作用蛋白，在一个与底物和前折叠蛋白结合都兼容的位置，特异地结合到几乎所有开放状态而非闭合状态的TRiC。

他们的数据支持一个模型，即TRiC在细胞内以接近满负荷的状态运作，折叠新合成的蛋白质。定义细胞内的TRiC周期和功能，为理解其在癌症和神经退行性疾病中的功能障碍奠定了基础。

附：英文原文

Title: In situ analysis reveals the TRiC duty cycle and PDCD5 as an open-state cofactor

Author: Xing, Huaipeng, Rosenkranz, Remus R. E., Rodriguez-Aliaga, Piere, Lee, Ting-Ting, Majtner, Tom, Bhm, Stefanie, Turoov, Beata, Frydman, Judith, Beck, Martin

Issue&Volume: 2024-12-11

Abstract: The ring-shaped chaperonin T-complex protein ring complex (TRiC; also known as chaperonin containing TCP-1, CCT) is an ATP-driven protein-folding machine that is essential for maintenance of cellular homeostasis1,2. Its dysfunction is related to cancer and neurodegenerative disease3,4. Despite its importance, how TRiC works in the cell remains unclear. Here we structurally analysed the architecture, conformational dynamics and spatial organization of the chaperonin TRiC in human cells using cryo-electron tomography. We resolved distinctive open, closed, substrate-bound and prefoldin-associated states of TRiC, and reconstructed its duty cycle in situ. The substrate-bound open and symmetrically closed TRiC states were equally abundant. Closed TRiC containing substrate forms distinctive clusters, indicative of spatial organization. Translation inhibition did not fundamentally change the distribution of duty cycle intermediates, but reduced substrate binding for all states as well as cluster formation. From our in-cell structures, we identified the programmed cell death protein 5 (PDCD5) as an interactor that specifically binds to almost all open but not closed TRiC, in a position that is compatible with both substrate and prefoldin binding. Our data support a model in which TRiC functions at near full occupancy to fold newly synthesized proteins inside cells. Defining the TRiC cycle and function inside cells lays the foundation to understand its dysfunction during cancer and neurodegeneration.

DOI: 10.1038/s41586-024-08321-z

Source: https://www.nature.com/articles/s41586-024-08321-z