title: Protomer Roles in Chloroplast Chaperonin Assembly and Function.
abstract: The individual roles of three chloroplast CPN60 protomers (CPN60α, CPN60β1, and CPN60β2) and whether and how they are assembled into functional chaperonin complexes are investigated in Chlamydomonas reinhardtii. Protein complexes containing all three potential subunits were identified in Chlamydomonas, and their co-expression in Escherichia coli yielded a homogeneous population of oligomers containing all three subunits (CPN60αβ1β2), with a molecular weight consistent with a tetradecameric structure. While homo-oligomers of CPN60β could form, they were dramatically reduced when CPN60α was present and homo-oligomers of CPN60β2 were readily changed into hetero-oligomers in the presence of ATP and other protomers. ATP hydrolysis caused CPN60 oligomers to disassemble and drove the purified protomers to reconstitute oligomers in vitro, suggesting that the dynamic nature of CPN60 oligomers is dependent on ATP. Only hetero-oligomeric CPN60αβ1β2, containing CPN60α, CPN60β1, and CPN60β2 subunits in a 5:6:3 ratio, cooperated functionally with GroES. The combination of CPN60α and CPN60β subunits, but not the individual subunits alone, complemented GroEL function in E. coli with subunit recognition specificity. Down-regulation of the CPN60α subunit in Chlamydomonas resulted in a slow growth defect and an inability to grow autotrophically, indicating the essential role of CPN60α in vivo.
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Cuicui
authors.initials: C
authors.lastname: Bai
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Zongyang
authors.initials: Z
authors.lastname: Lv
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Shijia
authors.initials: S
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
authors.affiliation: Key Laboratory of Molecular Development Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Liyan
authors.initials: L
authors.lastname: Gao
authors.affiliation: Key Laboratory of Molecular Development Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Yingchun
authors.initials: Y
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Zhixi
authors.initials: Z
authors.lastname: Tian
authors.affiliation: Laboratory of Protein and Peptide Pharmaceuticals and Laboratory of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Jifeng
authors.initials: J
authors.lastname: Wang
authors.affiliation: Laboratory of Protein and Peptide Pharmaceuticals and Laboratory of Proteomics, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Fuquan
authors.initials: F
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China. Electronic address: cmliu@genetics.ac.cn.
authors.forename: Cuimin
authors.initials: C
authors.lastname: Liu
mesh_terms: D029681:Arabidopsis Proteins / Q000235:genetics; D018834:Chaperonin 60 / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D021122:Protein Subunits / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D018834:Chaperonin 60; D021122:Protein Subunits
keywords: Cpn60; assembly; chaperonin; photosynthesis; protomer