A Gradient of ATP Affinities Generates an Asymmetric Power Stroke Driving the Chaperonin TRIC/CCT Folding Cycle

• Published in: Cell reports (Cambridge) Vol. 2; no. 4; pp. 866 - 877
• Main Authors: Reissmann, Stefanie, Joachimiak, Lukasz A., Chen, Bryan, Meyer, Anne S., Nguyen, Anthony, Frydman, Judith
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 25.10.2012; Elsevier
• Subjects: Adenosine Triphosphate - metabolism; Amino Acid Sequence; Animals; Binding Sites; Catalytic Domain; Cattle; Chaperonin Containing TCP-1 - chemistry; Chaperonin Containing TCP-1 - metabolism; Molecular Sequence Data; Protein Binding; Protein Folding; Protein Subunits - chemistry; Protein Subunits - metabolism; Saccharomyces cerevisiae - metabolism
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2012.08.036

The eukaryotic chaperonin TRiC/CCT uses ATP cycling to fold many essential proteins that other chaperones cannot fold. This 1 MDa hetero-oligomer consists of two identical stacked rings assembled from eight paralogous subunits, each containing a conserved ATP-binding domain. Here, we report a dramatic asymmetry in the ATP utilization cycle of this ring-shaped chaperonin, despite its apparently symmetric architecture. Only four of the eight different subunits bind ATP at physiological concentrations. ATP binding and hydrolysis by the low-affinity subunits is fully dispensable for TRiC function in vivo. The conserved nucleotide-binding hierarchy among TRiC subunits is evolutionarily modulated through differential nucleoside contacts. Strikingly, high- and low-affinity subunits are spatially segregated within two contiguous hemispheres in the ring, generating an asymmetric power stroke that drives the folding cycle. This unusual mode of ATP utilization likely serves to orchestrate a directional mechanism underlying TRiC/CCT's unique ability to fold complex eukaryotic proteins. [Display omitted] ► The eight paralogous TRiC subunits display hierarchical ATP occupancy ► Conservation of nucleoside contacts among TRiC orthologs mirrors ATP affinity ► ATP binding and hydrolysis in the low-affinity subunits are dispensable for life ► ATP usage segregates asymmetrically into two hemispheres of the chaperonin ring The eukaryotic chaperonin TRiC/CCT consists of two identical stacked rings assembled from eight paralogous subunits, each containing an ATP-binding domain. ATP hydrolysis induces lid closure, resulting in substrate encapsulation within the central folding chamber. Joachimiak, Frydman, and colleagues discover that paralogous subunits have strikingly different affinities for ATP conserved in evolution. High- and low-affinity subunits are spatially segregated within two contiguous hemispheres in the ring, thus generating an asymmetric power stroke that efficiently uses ATP to drive lid closure.