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

Abstract

SUMMARY 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.

Human CCT4 and CCT5 Chaperonin Subunits Expressed in Escherichia coli Form Biologically Active Homo-oligomers

“…It has recently been found that the different CCT subunits of TRiC bind ATP with different affinities (28). For the TRiC chaperonin to close, every subunit does not need to bind ATP, unlike the ATP-binding mechanism in GroEL/ES (2), where every GroEL subunit has to bind an ATP for closure.…”

Folding of large multidomain proteins by partial encapsulation in the chaperonin TRiC/CCT

“…closure (35,36,63,64). Thus, a flexibly attached folded domain, itself not interacting with TRiC (such as GFP in the actin fusions), might be excluded from the cavity, adopting a topology in which the extended linker traverses the central channel (Fig.…”

Asymmetric perturbations of signalling oligomers

“…A recent comparative XRC and cryo-EM study has revealed that functional transition of GroEL into a relaxed state is associated with breaking of two salt bridges and transient asymmetry of the apical domains (Fei et al, 2013). Asymmetries can be also revealed in the octameric rings of TRiC, an eukaryotic group II chaperonin; in its ATP-binding hierarchy; and even in its transition states (Cong et al, 2012;Reissmann et al, 2012).…”