Plant Molecular Biology

, Volume 40, Issue 3, pp 409–418 | Cite as

Molecular characterization of DnaK from the halotolerant cyanobacterium Aphanothece halophytica for ATPase, protein folding, and copper binding under various salinity conditions

  • Takashi Hibino
  • Nobuo Kaku
  • Hirofumi Yoshikawa
  • Tetsuko Takabe
  • Teruhiro Takabe


Previously, it was found that the dnaK1 gene of the halotolerant cyanobacterium Aphanothece halophytica encodes a polypeptide of 721 amino acids which has a long C-terminal region rich in acidic amino acid residues. To understand whether the A. halophytica DnaK1 possesses chaperone activity at high salinity and to clarify the role of the extra C-terminal amino acids, a comparative study examined three kinds of DnaK molecules for ATPase activity as well as the refolding activity of other urea-denatured proteins under various salinity conditions. DnaK1s from A. halophytica and Synechococcus sp. PCC 7942 and the C-terminal deleted A. halophytica DnaK1 were expressed in Escherichia coli and purified. The ATPase activity of A. halophytica DnaK1 was very high even at high salinity (1.0 M NaCl or KCl), whereas this activity in Synechococcus PCC 7942 DnaK1 decreased with increasing concentrations of NaCl or KCl. The salt dependence on the refolding activity of urea-denatured lactate dehydrogenase by DnaK1s was similar to that of ATPase activity of the respective DnaK1s. The deletion of the C-terminal amino acids of A. halophytica DnaK1 had no effect on the ATPase activity, but caused a significant decrease in the refolding activity of other denatured proteins. These facts indicate that the extra C-terminal region of A. halophytica DnaK1 plays an important role in the refolding of other urea-denatured proteins at high salinity. Furthermore, it was shown that DnaK1 could assist the copper binding of precursor apo-plastocyanin as well as that of mature apo-plastocyanin during the folding of these copper proteins.

Aphanothece halophytica ATPase chaperones DnaK salt tolerance plastocyanin 


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Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • Takashi Hibino
    • 1
  • Nobuo Kaku
    • 2
  • Hirofumi Yoshikawa
    • 3
  • Tetsuko Takabe
    • 4
  • Teruhiro Takabe
    • 1
  1. 1.Department of Chemistry, Faculty of Science and TechnologyMeijo UniversityTenpaku-ku, Nagoya, AichiJapan
  2. 2.Research Institute of Meijo UniversityTenpaku-ku, Nagoya, AichiJapan
  3. 3.Department of Bio-scienceTokyo University of AgricultureSetagaya-ku, TokyoJapan
  4. 4.BioScience Center, School of Agricultural ScienceNagoya UniversityChikusa-ku, Nagoya, AichiJapan

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