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  • Title: Cytosolic chaperonin protects folding intermediates of Gbeta from aggregation by recognizing hydrophobic beta-strands.
    Author: Kubota S, Kubota H, Nagata K.
    Journal: Proc Natl Acad Sci U S A; 2006 May 30; 103(22):8360-5. PubMed ID: 16717193.
    Abstract:
    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.
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