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The ATP-powered gymnastics of TRiC/CCT: an asymmetric protein folding machine with a symmetric origin story.

ABSTRACT: The eukaryotic chaperonin TRiC/CCT is a large hetero-oligomeric complex that plays an essential role assisting cellular protein folding and suppressing protein aggregation. It consists of two rings, and each composed of eight different subunits; non-native polypeptides bind and fold in an ATP-dependent manner within their central chamber. Here, we review recent advances in our understanding of TRiC structure and mechanism enabled by application of hybrid structural methods including the integration of cryo-electron microscopy with distance constraints from crosslinking mass spectrometry. These new insights are revealing how the different TRiC/CCT subunits create asymmetry in its ATP-driven conformational cycle and its interaction with non-native polypeptides, which ultimately underlie its unique ability to fold proteins that cannot be folded by other chaperones.

SUBMITTER: Gestaut D

PROVIDER: S-EPMC6776438 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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The ATP-powered gymnastics of TRiC/CCT: an asymmetric protein folding machine with a symmetric origin story.

Gestaut Daniel D Limatola Antonio A Joachimiak Lukasz L Frydman Judith J

Current opinion in structural biology 20190409

The eukaryotic chaperonin TRiC/CCT is a large hetero-oligomeric complex that plays an essential role assisting cellular protein folding and suppressing protein aggregation. It consists of two rings, and each composed of eight different subunits; non-native polypeptides bind and fold in an ATP-dependent manner within their central chamber. Here, we review recent advances in our understanding of TRiC structure and mechanism enabled by application of hybrid structural methods including the integrat ...[more]

PMID: 30978594

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A gradient of ATP affinities generates an asymmetric power stroke driving the chaperonin TRIC/CCT folding cycle.

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Structural visualization of the tubulin folding pathway directed by human chaperonin TRiC/CCT.

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Co-expression of CCT subunits hints at TRiC assembly.

Project description:The eukaryotic cytosolic chaperonin, t-complex polypeptide 1 (TCP-1) ring complex or TRiC, is responsible for folding a tenth of the proteins in the cell. TRiC is a double-ringed barrel with each ring composed of eight different CCT (chaperonin containing TCP-1) subunits. In order for the subunits to assemble together into mature TRiC, which is believed to contain one and only one of each of these subunits per ring, they must be translated from different chromosomes, correctly folded and assembled. When expressed alone in Escherichia coli, the subunits CCT4 and CCT5, interestingly, form TRiC-like homo-oligomeric rings. To explore potential subunit-subunit interactions, we co-expressed these homo-oligomerizing CCT4 and CCT5 subunits or the archaeal chaperonin Mm-Cpn (Methanococcus maripaludis chaperonin) with CCT1-8, one at a time. We found that CCT5 shifted all of the CCT subunits, with the exception of CCT6, into double-barrel TRiC-like complexes, while CCT4 only interacted with CCT5 and CCT8 to form chaperonin rings. We hypothesize that these specific interactions may be due to the formation of hetero-oligomers in E. coli, although more work is needed for validation. We also observed the interaction of CCT5 and Mm-Cpn with smaller fragments of the CCT subunits, confirming their intrinsic chaperone activity. Based on this hetero-oligomer data, we propose that TRiC assembly relies on subunit exchange with some stable homo-oligomers, possibly CCT5, as base assembly units. Eventually, analysis of CCT arrangement in various tissues and at different developmental times is anticipated to provide additional insight on TRiC assembly and CCT subunit composition.

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The molecular architecture of the eukaryotic chaperonin TRiC/CCT.

Project description:TRiC/CCT is a highly conserved and essential chaperonin that uses ATP cycling to facilitate folding of approximately 10% of the eukaryotic proteome. This 1 MDa hetero-oligomeric complex consists of two stacked rings of eight paralogous subunits each. Previously proposed TRiC models differ substantially in their subunit arrangements and ring register. Here, we integrate chemical crosslinking, mass spectrometry, and combinatorial modeling to reveal the definitive subunit arrangement of TRiC. In vivo disulfide mapping provided additional validation for the crosslinking-derived arrangement as the definitive TRiC topology. This subunit arrangement allowed the refinement of a structural model using existing X-ray diffraction data. The structure described here explains all available crosslink experiments, provides a rationale for previously unexplained structural features, and reveals a surprising asymmetry of charges within the chaperonin folding chamber.

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