Verna and Marrs McLean Department of Biochemistry and Molecular Biology, National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, TX 77030, USA.
EMBO J. 2012 Feb 1;31(3):720-30. doi: 10.1038/emboj.2011.366. Epub 2011 Nov 1.
The eukaryotic group II chaperonin TRiC/CCT is a 16-subunit complex with eight distinct but similar subunits arranged in two stacked rings. Substrate folding inside the central chamber is triggered by ATP hydrolysis. We present five cryo-EM structures of TRiC in apo and nucleotide-induced states without imposing symmetry during the 3D reconstruction. These structures reveal the intra- and inter-ring subunit interaction pattern changes during the ATPase cycle. In the apo state, the subunit arrangement in each ring is highly asymmetric, whereas all nucleotide-containing states tend to be more symmetrical. We identify and structurally characterize an one-ring closed intermediate induced by ATP hydrolysis wherein the closed TRiC ring exhibits an observable chamber expansion. This likely represents the physiological substrate folding state. Our structural results suggest mechanisms for inter-ring-negative cooperativity, intra-ring-positive cooperativity, and protein-folding chamber closure of TRiC. Intriguingly, these mechanisms are different from other group I and II chaperonins despite their similar architecture.
真核生物 II 类伴侣蛋白 TRiC/CCT 是一个由 16 个亚基组成的复合物，其中 8 个亚基彼此相似但又有区别，它们排列成两个堆叠的环。底物在中央腔中的折叠是由 ATP 水解触发的。我们呈现了五个无对称性约束的 TRiC 在 apo 和核苷酸诱导状态下的 cryo-EM 结构。这些结构揭示了在 ATP 酶循环中，亚基间和环内相互作用模式的变化。在 apo 状态下，每个环中的亚基排列高度不对称，而所有含核苷酸的状态往往更对称。我们鉴定并结构表征了由 ATP 水解诱导的一环封闭中间态，其中封闭的 TRiC 环显示出可观察到的腔扩张。这可能代表了生理上的底物折叠状态。我们的结构结果表明了 TRiC 的环间负协同作用、环内正协同作用和蛋白折叠腔封闭的机制。有趣的是，尽管它们的结构相似，但这些机制与其他 I 类和 II 类伴侣蛋白不同。
