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Cytosolic chaperonin protects folding intermediates of Gbeta from aggregation by recognizing hydrophobic beta-strands.

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.

SUBMITTER: Kubota S

PROVIDER: S-EPMC1482499 | biostudies-literature | 2006 May

REPOSITORIES: biostudies-literature

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Cytosolic chaperonin protects folding intermediates of Gbeta from aggregation by recognizing hydrophobic beta-strands.

Kubota Susumu S Kubota Hiroshi H Nagata Kazuhiro K

Proceedings of the National Academy of Sciences of the United States of America 20060522 22

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 tha ...[more]

PMID: 16717193

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Project description:Group I chaperonins are large cylindrical-shaped nano-machines that function as a central hub in the protein quality control system in the bacterial cytosol, mitochondria and chloroplasts. In chloroplasts, proteins newly synthesized by chloroplast ribosomes, unfolded by diverse stresses, or translocated from the cytosol run the risk of aberrant folding and aggregation. The chloroplast chaperonin system assists these proteins in folding into their native states. A widely known protein folded by chloroplast chaperonin is the large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), an enzyme responsible for the fixation of inorganic CO2 into organic carbohydrates during photosynthesis. Chloroplast chaperonin was initially identified as a Rubisco-binding protein. All photosynthetic eucaryotes genomes encode multiple chaperonin genes which can be divided into ? and ? subtypes. Unlike the homo-oligomeric chaperonins from bacteria and mitochondria, chloroplast chaperonins are more complex and exists as intricate hetero-oligomers containing both subtypes. The Group I chaperonin requires proper interaction with a detachable lid-like co-chaperonin in the presence of ATP and Mg2+ for substrate encapsulation and conformational transition. Besides the typical Cpn10-like co-chaperonin, a unique co-chaperonin consisting of two tandem Cpn10-like domains joined head-to-tail exists in chloroplasts. Since chloroplasts were proposed as sensors to various environmental stresses, this diversified chloroplast chaperonin system has the potential to adapt to complex conditions by accommodating specific substrates or through regulation at both the transcriptional and post-translational levels. In this review, we discuss recent progress on the unique structure and function of the chloroplast chaperonin system based on model organisms Chlamydomonas reinhardtii and Arabidopsis thaliana. Knowledge of the chloroplast chaperonin system may ultimately lead to successful reconstitution of eukaryotic Rubisco in vitro.

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Cytosolic chaperonin protects folding intermediates of Gbeta from aggregation by recognizing hydrophobic beta-strands.

Publications

Cytosolic chaperonin protects folding intermediates of Gbeta from aggregation by recognizing hydrophobic beta-strands.

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