a chaperonin subunit with unique structures is essential for folding of a specific substrate一种具有独特结构的chaperonin亚基对特定底物的折叠至关重要.pdfVIP

A Chaperonin Subunit with Unique Structures Is Essential for Folding of a Specific Substrate 1 2 3 4 3 Lianwei Peng , Yoichiro Fukao , Fumiyoshi Myouga , Reiko Motohashi , Kazuo Shinozaki , Toshiharu Shikanai1* 1 Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, Japan, 2 Plant Global Educational Project, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Takayama, Ikoma, Nara, Japan, 3 Gene Discovery Research Group, RIKEN Plant Science Center, Yokohama, Japan, 4 Faculty of Agriculture, University of Shizuoka, Shizuoka, Japan 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 Cpn60b4 forms a heterooligomeric Cpn60 complex with Cpn60a 1 and Cpn60b1–b3 and is specifically required for the folding of NdhH, a subunit of the chloroplast NADH dehydrogenase-like complex (NDH). Other Cpn60b subunits cannot complement the function of Cpn60b4. Furthermore, the unique C-terminus of Cpn60b4 is required for the full activity of the unique Cpn60 complex containing Cpn60b4 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 C