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Structural insight into the cooperation of chloroplast chaperonin subunits.

ABSTRACT: Chloroplast chaperonin, consisting of multiple subunits, mediates folding of the highly abundant protein Rubisco with the assistance of co-chaperonins. ATP hydrolysis drives the chaperonin allosteric cycle to assist substrate folding and promotes disassembly of chloroplast chaperonin. The ways in which the subunits cooperate during this cycle remain unclear.Here, we report the first crystal structure of Chlamydomonas chloroplast chaperonin homo-oligomer (CPN60?1) at 3.8 Å, which shares structural topology with typical type I chaperonins but with looser compaction, and possesses a larger central cavity, less contact sites and an enlarged ATP binding pocket compared to GroEL. The overall structure of Cpn60 resembles the GroEL allosteric intermediate state. Moreover, two amino acid (aa) residues (G153, G154) conserved among Cpn60s are involved in ATPase activity regulated by co-chaperonins. Domain swapping analysis revealed that the monomeric state of CPN60? is controlled by its equatorial domain. Furthermore, the C-terminal segment (aa 484-547) of CPN60? influenced oligomer disassembly and allosteric rearrangement driven by ATP hydrolysis. The entire equatorial domain and at least one part of the intermediate domain from CPN60? are indispensable for functional cooperation with CPN60?1, and this functional cooperation is strictly dependent on a conserved aa residue (E461) in the CPN60? subunit.The first crystal structure of Chlamydomonas chloroplast chaperonin homo-oligomer (CPN60?1) is reported. The equatorial domain maintained the monomeric state of CPN60? and the C-terminus of CPN60? affected oligomer disassembly driven by ATP. The cooperative roles of CPN60 subunits were also established.

SUBMITTER: Zhang S

PROVIDER: S-EPMC4828840 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Structural insight into the cooperation of chloroplast chaperonin subunits.

Zhang Shijia S Zhou Huan H Yu Feng F Bai Cuicui C Zhao Qian Q He Jianhua J Liu Cuimin C

BMC biology 20160412

<h4>Background</h4>Chloroplast chaperonin, consisting of multiple subunits, mediates folding of the highly abundant protein Rubisco with the assistance of co-chaperonins. ATP hydrolysis drives the chaperonin allosteric cycle to assist substrate folding and promotes disassembly of chloroplast chaperonin. The ways in which the subunits cooperate during this cycle remain unclear.<h4>Results</h4>Here, we report the first crystal structure of Chlamydomonas chloroplast chaperonin homo-oligomer (CPN60β ...[more]

PMID: 27072913

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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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Structural insight into the cooperation of chloroplast chaperonin subunits.

Publications

Structural insight into the cooperation of chloroplast chaperonin subunits.

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