TRiC (complex)

T-complex protein Ring Complex (TRiC), otherwise known as Chaperonin Containing TCP-1 (CCT),^[a] is a multiprotein complex and the chaperonin of eukaryotic cells. Like the bacterial GroEL, the TRiC complex aids in the folding of ~10% of the proteome, and actin and tubulin are some of its best known substrates.^[2][3] TRiC is an example of a biological machine that folds substrates within the central cavity of its barrel-like assembly using the energy from ATP hydrolysis.

Structure of Saccharomyces cerevisiae TRiC in the AMP-PNP bound state (PDB 5GW5).^[1]

Subunits

The human TRiC complex is formed by two rings containing 8 similar but non-identical subunits, each with molecular weights of ~60 kDa. The two rings are stacked in an asymmetrical fashion, forming a barrel-like structure with a molecular weight of ~1 MDa.^[2][3]

Subunit	MW (kDa)[A]	Features
TCP1 (CCT1/α)	60
CCT2 (β)	57
CCT3 (γ)	61
CCT4 (δ)	58
CCT5 (ε)	60
CCT6 (ζ)	58	Two copies in human genome, CCT6A and CCT6B.
CCT7 (η)	59
CCT8 (θ)	60

^A Molecular weight of human subunits.

Counterclockwise from the exterior, each ring is made of the subunits in the following order: 6-8-7-5-2-4-1-3.^[4]

Evolution

The CCT evolved from the archaeal thermosome ~2Gya, with the two subunits diversifying into multiple units. The CCT changed from having one type of subunit, to having two, three, five, and finally eight types.^{[4]: fig. 4}

See also

• Chaperone
• Chaperonin
• Heat shock protein

Notes

1. The term "TCP-1" is variously expanded as "T-complex protein 1" and "tailless complex polypeptide 1". The "T-complex" is the same as tailless complex, a CCT locus associated with tail length in mice.