TRiC (complex)

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

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.

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.

References

1. Zang, Yunxiang; Jin, Mingliang; Wang, Huping; Cui, Zhicheng; Kong, Liangliang; Liu, Caixuan; Cong, Yao (2016-10-24). "Staggered ATP binding mechanism of eukaryotic chaperonin TRiC (CCT) revealed through high-resolution cryo-EM". Nature Structural & Molecular Biology. 23 (12). Springer Science and Business Media LLC: 1083–1091. doi:10.1038/nsmb.3309. ISSN 1545-9993. PMID 27775711. S2CID 12001964.
2. Balchin, David; Hayer-Hartl, Manajit; Hartl, F. Ulrich (2016-06-30). "In vivo aspects of protein folding and quality control". Science. 353 (6294). American Association for the Advancement of Science (AAAS): aac4354. doi:10.1126/science.aac4354. hdl:11858/00-001M-0000-002B-0856-C. ISSN 0036-8075. PMID 27365453. S2CID 5174431.
3. Gestaut, Daniel; Limatola, Antonio; Joachimiak, Lukasz; Frydman, Judith (2019). "The ATP-powered gymnastics of TRiC/CCT: an asymmetric protein folding machine with a symmetric origin story". Current Opinion in Structural Biology. 55. Elsevier BV: 50–58. doi:10.1016/j.sbi.2019.03.002. ISSN 0959-440X. PMC 6776438. PMID 30978594.
4. Willison, KR (5 October 2018). "The structure and evolution of eukaryotic chaperonin-containing TCP-1 and its mechanism that folds actin into a protein spring". The Biochemical Journal. 475 (19): 3009–3034. doi:10.1042/BCJ20170378. hdl:10044/1/63924. PMID 30291170. S2CID 52923821.