title: Symmetry-free cryo-EM structures of the chaperonin TRiC along its ATPase-driven conformational cycle.
abstract: 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.
authors: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, National Center for Macromolecular Imaging, Baylor College of Medicine, Houston, TX 77030, USA.
authors: Yao
authors: Y
authors: Cong
authors: Gunnar F
authors: GF
authors: Schröder
authors: Anne S
authors: AS
authors: Meyer
authors: Joanita
authors: J
authors: Jakana
authors: Boxue
authors: B
authors: Ma
authors: Matthew T
authors: MT
authors: Dougherty
authors: Michael F
authors: MF
authors: Schmid
authors: Stefanie
authors: S
authors: Reissmann
authors: Michael
authors: M
authors: Levitt
authors: Steven L
authors: SL
authors: Ludtke
authors: Judith
authors: J
authors: Frydman
authors: Wah
authors: W
authors: Chiu
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D018833:Chaperonins / Q000737:chemistry* / Q000378:metabolism; D020285:Cryoelectron Microscopy; D006868:Hydrolysis; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding
chemical_list: D000251:Adenosine Triphosphatases; D018833:Chaperonins