Alternative processing of arabidopsis Hsp70 precursors during protein import into chloroplasts

• Published in: Bioscience, biotechnology, and biochemistry Vol. 72; no. 11; pp. 2926 - 2935
• Main Authors: Ratnayake, R.M.U.(Ehime Univ., Matsuyama (Japan)), Inoue, H, Nonami, H, Akita, M
• Format: Journal Article
• Language: English
• Published: Tokyo Japan Society for Bioscience, Biotechnology, and Agrochemistry 01-11-2008; Japan Society for Bioscience Biotechnology and Agrochemistry; Oxford University Press
• Subjects: Amino Acid Sequence; Animals; Antibodies, Monoclonal - metabolism; Arabidopsis; Arabidopsis - cytology; Arabidopsis - metabolism; ARABIDOPSIS THALIANA; Biological and medical sciences; chloroplast; CHLOROPLASTE; CHLOROPLASTS; Chloroplasts - metabolism; CLOROPLASTO; Computational Biology; Fundamental and applied biological sciences. Psychology; Glycine; Hsp70; HSP70 Heat-Shock Proteins - chemistry; HSP70 Heat-Shock Proteins - metabolism; Humans; Mice; Molecular Sequence Data; PEPTIDASAS; PEPTIDASE; PEPTIDASES; Plant Proteins - chemistry; Plant Proteins - metabolism; PROCESAMIENTO; PROCESSING; protein import; Protein Precursors - chemistry; Protein Precursors - metabolism; Protein Transport; PROTEINAS; PROTEINE; PROTEINS; Time Factors; TRAITEMENT; TRANSLOCATION; TRASLOCACION; Trypsin - metabolism; Hsp70; process-ing; Cruciferae; Arabidopsis; Dicotyledones; Angiospermae; Spermatophyta; Operating process; protein import; Precursor; Chloroplast; Protein
• DOI: 10.1271/bbb.80408
• EISSN: 1347-6947
• ISSN: 0916-8451

During protein import into chloroplasts, one of the Hsp70 proteins in pea (Hsp70-IAP), previously reported to localize in the intermembrane space of chloroplasts, was found to interact with the translocating precursor protein but the gene for Hsp70-IAP has not been identified yet. In an attempt to identify the Arabidopsis homolog of Hsp70-IAP, we employed an in vitro protein import assay to determine the localization of three Arabidopsis Hsp70 homologs (AtHsp70-6 through 8), predicted for chloroplast targeting. AtHsp70-6 and AtHsp70-7 were imported into chloroplasts and processed into similar-sized mature forms. In addition, a smaller-sized processed form of AtHsp70-6 was observed. All the processed forms of both AtHsp70 proteins were localized in the stroma. Organelle-free processing assays revealed that the larger processed forms of both AtHsp70-6 and AtHsp70-7 were cleaved by stromal processing peptidase, whereas the smaller processed form of AtHsp70-6 was produced by an unspecified peptidase.