hsp70-protein complexes. Complex stability and conformation of bound substrate protein.
The presence of bound substrate protein increases the thermostability of hsp70 molecular chaperones (heat shock proteins of molecular mass 70 kDa). Complexes between hsp70 and unfolded substrate proteins were isolated by size-exclusion high performance liquid chromatography. The isolated complexes were observed to dissociate at a significant rate even in the absence of ATP. The presence of ADP caused a substantial increase in the stability of the complex. Both ADP and inorganic phosphate were found to inhibit the ATP-induced dissociation of complex. ADP was also observed to increase both the rate of complex formation and its stability as a function of temperature, suggesting an important regulatory role for nucleotides during heat shock. Circular dichroism and fluorescence studies of the complex between DnaK and a thermally unstable mutant of staphylococcal nuclease indicate that the bound substrate protein is significantly unfolded. A model for hsp70 cycle of complex formation and dissociation, which accounts for the regulatory role of nucleotides, is proposed.
Palleros
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Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
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Reid
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Fink
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D000244:Adenosine Diphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002942:Circular Dichroism; D029968:Escherichia coli Proteins; D005454:Fluorescence Polarization; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D007768:Lactalbumin / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000502:physiology*; D008836:Micrococcal Nuclease / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D011509:Proteoglycans / Q000502:physiology*; D053667:Syndecans; D013816:Thermodynamics
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008562:Membrane Glycoproteins; D011509:Proteoglycans; D053667:Syndecans; D000244:Adenosine Diphosphate; D007768:Lactalbumin; D008836:Micrococcal Nuclease; C063842:dnaK protein, E coli