title: A chaperonin subunit with unique structures is essential for folding of a specific substrate.
abstract: Type I chaperonins are large, double-ring complexes present in bacteria (GroEL), mitochondria (Hsp60), and chloroplasts (Cpn60), which are involved in mediating the folding of newly synthesized, translocated, or stress-denatured proteins. In Escherichia coli, GroEL comprises 14 identical subunits and has been exquisitely optimized to fold its broad range of substrates. However, multiple Cpn60 subunits with different expression profiles have evolved in chloroplasts. Here, we show that, in Arabidopsis thaliana, the minor subunit Cpn60β4 forms a heterooligomeric Cpn60 complex with Cpn60α1 and Cpn60β1-β3 and is specifically required for the folding of NdhH, a subunit of the chloroplast NADH dehydrogenase-like complex (NDH). Other Cpn60β subunits cannot complement the function of Cpn60β4. Furthermore, the unique C-terminus of Cpn60β4 is required for the full activity of the unique Cpn60 complex containing Cpn60β4 for folding of NdhH. Our findings suggest that this unusual kind of subunit enables the Cpn60 complex to assist the folding of some particular substrates, whereas other dominant Cpn60 subunits maintain a housekeeping chaperonin function by facilitating the folding of other obligate substrates.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, Japan.
authors.forename: Lianwei
authors.initials: L
authors.lastname: Peng
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Fukao
authors.forename: Fumiyoshi
authors.initials: F
authors.lastname: Myouga
authors.forename: Reiko
authors.initials: R
authors.lastname: Motohashi
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Shikanai
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism*; D018834:Chaperonin 60 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D002846:Chromatography, Affinity; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D009154:Mutation; D017510:Protein Folding; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D018834:Chaperonin 60