TCP1 complex is a molecular chaperone in tubulin biogenesis

Abstract

A role in folding of newly translated proteins in the cytosol of eukaryotes has been proposed for t-complex polypeptide-1 (TCP1), although its molecular targets have not yet been identified. Tubulin is a major cytosolic protein whose assembly into microtubules is critical to many cellular processes. Although numerous studies have focused on the expression of tubulin, little is known about the processes whereby newly translated tubulin subunits acquire conformations that enable them to form alpha-beta-heterodimers. We examined the biogenesis of alpha- and beta-tubulin in rabbit reticulocyte lysate, and report here that newly translated tubulin subunits entered a 900K complex in a protease-sensitive conformation. Addition of Mg-ATP, but not nonhydrolysable analogues, released the tubulin subunits as assembly-competent protein with a conformation that was relatively protease-resistant. The 900K complex purified from reticulocyte lysate contained as its major constituent a 58K protein that cross-reacted with a monoclonal antiserum against mouse TCP1. We conclude that TCP1 functions as a cytosolic chaperone in the biogenesis of tubulin.

Firefly luciferase mutants as sensors of proteome stress

“…Interestingly, Group II chaperonins share sequence homology with GroEL at the ATP binding site, but they differ considerably in sequence of the substrate binding site (Kim et al, 1994;Spiess et al, 2006). TRiC, like GroEL, is an essential protein since at least two cytoskeletal proteins, actin and tubulin, are obligate substrates of TRiC (Dobrzynski et al, 1996;Gao et al, 1992;Llorca et al, 1999;Yaffe et al, 1992). 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).…”

Human TRiC complex purified from HeLa cells contains all eight CCT subunits and is active in vitro

“…This complex consisted of a set of polypeptides between 55 and 60 kDa; one of which was recognized by the TCP-1 antibody (Yaffe et al 1992). Concurrently, preliminary characterization of human and mouse TCP-1 found that in both species TCP-1 made a complex of approximately 900 kDa and that TCP-1 associated with four to six unidentified polypeptides and two Hsp70 homologs (Lewis et al 1992).…”

“…TRiC was first identified in rabbit reticulocytes when it was found that newly made tubulin subunits entered a 900-kDa complex before becoming competent to assemble into microtubules (Yaffe et al 1992). This complex consisted of a set of polypeptides between 55 and 60 kDa; one of which was recognized by the TCP-1 antibody (Yaffe et al 1992).…”

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

“…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].…”