Cytosolic chaperonin protects folding intermediates of Gbeta from aggregation by recognizing hydrophobic beta-strands.
Cytosolic chaperonin containing t-complex polypeptide 1 (CCT)/TRiC is a group II chaperonin that assists in the folding of newly synthesized proteins. It is a eukaryotic homologue of the bacterial group I chaperonin GroEL. In contrast to the well studied functions of GroEL, the substrate recognition mechanism of CCT/TRiC is poorly understood. Here, we established a system for analyzing CCT/TRiC functions by using a reconstituted protein synthesis by using recombinant elements system and show that CCT/TRiC strongly recognizes WD40 proteins particularly at hydrophobic beta-strands. Using the G protein beta subunit (Gbeta), a WD40 protein that is very rich in beta-sheets, as a model substrate, we found that CCT/TRiC prevents aggregation and assists in folding of Gbeta, whereas GroEL does not. Gbeta has a seven-bladed beta-propeller structure; each blade is formed from a WD40 repeat sequence encoding four beta-strands. Detailed mutational analysis of Gbeta indicated that CCT/TRiC, but not GroEL, preferentially recognizes hydrophobic residues aligned on surfaces of beta-strands in the second WD40 repeat of Gbeta. These findings indicate that one of the CCT/TRiC-specific targets is hydrophobic beta-strands, which are highly prone to aggregation.
Kubota
Susumu
S
Department of Molecular and Cellular Biology and Core Research for Evolutional Science and Technology/Japan Science and Technology Agency, Institute for Frontier Medical Sciences, Kyoto University, Kyoto 606-8397, Japan. hkubota@frontier.kyoto-u.ac.jp
Kubota
Hiroshi
H
Nagata
Kazuhiro
K
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D018834:Chaperonin 60 / Q000378:metabolism; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000378:metabolism; D016415:Sequence Alignment
D000199:Actins; D018834:Chaperonin 60; D021122:Protein Subunits; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins; D019204:GTP-Binding Proteins