Chloroplasts have a novel Cpn10 in addition to Cpn20 as co-chaperonins in Arabidopsis thaliana.
Previously, we characterized a mitochondrial co-chaperonin (Cpn10) and a chloroplast co-chaperonin (Cpn20) from Arabidopsis thaliana (Koumoto, Y., Tsugeki, R., Shimada, T., Mori, H., Kondo, M., Hara-Nishimura, I., and Nishimura, M. (1996) Plant J. 10, 1119-1125; Koumoto, Y., Shimada, T., Kondo, M., Takao, T., Shimonishi, Y., Hara-Nishimura, I., and Nishimura, M. (1999) Plant J. 17, 467-477). Here, we report a third co-chaperonin. The cDNA was 603 base pairs long, encoding a protein of 139 amino acids. From a sequence analysis, the protein was predicted to have one Cpn10 domain with an amino-terminal extension that might work as a chloroplast transit peptide. This novel Cpn10 was confirmed to be localized in chloroplasts, and we refer to it as chloroplast Cpn10 (chl-Cpn10). The phylogenic tree that was generated with amino acid sequences of other co-chaperonins indicates that chl-Cpn10 is highly divergent from the others. In the GroEL-assisted protein folding assay, about 30% of the substrates were refolded with chl-Cpn10, indicating that chl-Cpn10 works as a co-chaperonin. A Northern blot analysis revealed that mRNA for chl-Cpn10 is accumulated in the leaves and stems, but not in the roots. In germinating cotyledons, the accumulation of chl-Cpn10 was similar to that of chloroplastic proteins and accelerated by light. It was proposed that two kinds of co-chaperonins, Cpn20 and chl-Cpn10, work independently in the chloroplast.
Koumoto
Y
Y
Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Shimada
T
T
Kondo
M
M
Hara-Nishimura
I
I
Nishimura
M
M
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry; D029681:Arabidopsis Proteins; D001483:Base Sequence; D018835:Chaperonin 10 / Q000737:chemistry* / Q000235:genetics; D018834:Chaperonin 60 / Q000378:metabolism; D018833:Chaperonins / Q000737:chemistry* / Q000235:genetics; D002736:Chloroplasts / Q000737:chemistry* / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D056384:Group I Chaperonins; D015151:Immunoblotting; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010802:Phylogeny; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
D029681:Arabidopsis Proteins; D018835:Chaperonin 10; D018834:Chaperonin 60; C478767:Cpn20 protein, Arabidopsis; D018076:DNA, Complementary; D010455:Peptides; D012333:RNA, Messenger; D012313:RNA; D018833:Chaperonins; D056384:Group I Chaperonins