Function in protein folding of TRiC, a cytosolic ring complex containing TCP-1 and structurally related subunits.

Abstract

T‐complex polypeptide 1 (TCP‐1) was analyzed as a potential chaperonin (GroEL/Hsp60) equivalent of the eukaryotic cytosol. We found TCP‐1 to be part of a hetero‐oligomeric 970 kDa complex containing several structurally related subunits of 52–65 kDa. These members of a new protein family are assembled into a TCP‐1 ring complex (TRiC) which resembles the GroEL double ring. The main function of TRiC appears to be in chaperoning monomeric protein folding: TRiC binds unfolded polypeptides, thereby preventing their aggregation, and mediates the ATP‐dependent renaturation of unfolded firefly luciferase and tubulin. At least in vitro, TRiC appears to function independently of a small co‐chaperonin protein such as GroES. Folding of luciferase is mediated by TRiC but not by GroEL/ES. This suggests that the range of substrate proteins interacting productively with TRiC may differ from that of GroEL. We propose that TRiC mediates the folding of cytosolic proteins by a mechanism distinct from that of the chaperonins in specific aspects.

Firefly luciferase mutants as sensors of proteome stress

“…Unlike GroEL/ES which can act only post-translationally, TRiC has been shown to fold the discrete domains of firefly luciferase co-translationally (Frydman et al, 1994). From biochemical studies using unfolded firefly luciferase, actin and tubulin, it has been shown that while GroEL/ES failed to fold these model proteins, TRiC was able to mediate their folding, suggesting that it can interact with a different range of substrates via mechanism distinct from class I chaperonins (Frydman et al, 1992;Tian et al, 1995;Yam et al, 2008). A recent study of the TRiC interactome suggests that ~ 10% of newly synthesized cellular proteins, including actin, tubulin, cell cycle regulators and tumor suppressors are TRiC substrates.…”

The Tetrahymena chaperonin subunit CCTη gene is coexpressed with CCTγ gene during cilia biogenesis and cell sexual reproduction

“…This chaperonin, designated by Chaperonin Containing TCP1 (CCT) [10], is a hetero-oligomeric complex that in mammalian cytosol has a molecular mass of about 850-900 kDa. It is composed of seven to nine distinct polypeptides in the 52-65 kDa size range [10][11][12]. In mouse, genes coding for eight of the CCT subunit polypeptides have already been isolated and were designated as CCT0t (for the original TCP1), CCT [3 .... and CCT~ [10,13].…”

“…It has been shown that in vitro CCT is involved in the folding of actin [17,18], tubulin [12,19] and firefly luciferase [12,20]. In vivo studies indicate that newly synthesized a-and 13-tubulin and actin enter in a 900 kDa complex containing TCP1 and that tubulin is released from this complex competent to form heterodimers [21].…”

MgATP binding to the nucleotide‐binding domains of the eukaryotic cytoplasmic chaperonin induces conformational changes in the putative substrate‐binding domains

“…Both GroEL and CCT have a double-ring cylindrical structure and bind their protein substrates within the central cavity (Braig et al, 1993;Marco et al, 1994). Both require ATP binding and hydrolysis for their folding activity (Gao et al, 1992;Gething & Sambrook, 1992;Frydman et al, 1992;Yaffe et al, 1992). While GroEL is composed of identical subunits (7 per ring), CCT contains 8-9 nonidentical but related subunits per ring (Frydman et al, 1992;Gao et al, 1992;Lewis et al, 1992;Kim et al, 1994;Kubota et al, 1994Kubota et al, , 1995a.…”

“…Both require ATP binding and hydrolysis for their folding activity (Gao et al, 1992;Gething & Sambrook, 1992;Frydman et al, 1992;Yaffe et al, 1992). While GroEL is composed of identical subunits (7 per ring), CCT contains 8-9 nonidentical but related subunits per ring (Frydman et al, 1992;Gao et al, 1992;Lewis et al, 1992;Kim et al, 1994;Kubota et al, 1994Kubota et al, , 1995a. Another striking difference between the two chaperonins is their different substrate specificity.…”