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  • chaperones  (2)
  • Hsp70  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Molecular characterization of DnaK from the halotolerant cyanobacterium Aphanothece halophytica for ATPase, protein folding, and copper binding under various salinity conditions (1999)
    Springer
    Plant molecular biology 40 (1999), S. 409-418 
    Details
    ISSN: 1573-5028
    Keywords: Aphanothece halophytica ; ATPase ; chaperones ; DnaK ; salt tolerance ; plastocyanin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006273124726
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  • 2
    Electronic Resource
    Electronic Resource
    Isolation and characterization of a dnaK genomic locus in a halotolerant cyanobacterium Aphanothece halophytica (1997)
    Springer
    Plant molecular biology 35 (1997), S. 763-775 
    Details
    ISSN: 1573-5028
    Keywords: Aphanothece halophytica ; chaperones ; cyanobacteria ; DnaK ; Hsp70 ; salt tolerance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We cloned and characterized a genomic locus encoding a distinct member of the DnaK/Hsp70 family of molecular chaperones, dnaK1, from the halotolerant cyanobacterium Aphanothece halophytica. Co-expression of dnaK1 with a plant plastocyanin precursor in Escherichia coli resulted in a dramatic increase in the solubility of the plant protein. This indicates that A. halophytica dnaK1 encodes a functional protein possessing functions assigned to DnaK/Hsp70 chaperone members. The A. halophytica dnaK1 locus also encompasses grpE and dnaJ homologue genes in the order grpE-dnaK1-dnaJ. The transcript content of dnaK1 increased strongly upon subjecting cyanobacterial cells to heat stress. Northern analyses using specific probes indicated transcript species of 2.8, 2.2, 1.3, and 0.7 kb, which comprised grpE-dnaK1, dnaK1, dnaJ, and grpE, respectively. This indicates the presence of different terminators and/or heat stress promoters in this locus. Both dnaK1 transcript and protein levels increased in cyanobacterial cells transferred to hyperosmotic environments, suggesting a role of DnaK1 in the protection and/or recovery of A. halophytica from this particular stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005867420619
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    Paper (German National Licenses)
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