Role of the DnaK and HscA homologs of Hsp70 chaperones in protein folding in E.coli.
Folding of newly synthesized cytosolic proteins has been proposed to require assistance by Hsp70 chaperones. We investigated whether two Hsp70 homologs of Escherichia coli, DnaK and HscA, have this role in vivo. Double mutants lacking dnaK and hscA were viable and lacked defects in protein folding at intermediate temperature. After heat shock, a subpopulation of pre-existing proteins slowly aggregated in mutants lacking DnaK, but not HscA, whereas the bulk of newly synthesized proteins displayed wild-type solubility. For thermolabile firefly luciferase, DnaK was dispensable for de novo folding at 30 degrees C, but essential for aggregation prevention during heat shock and subsequent refolding. DnaK and HscA are thus not strictly essential for folding of newly synthesized proteins. DnaK instead has functions in refolding of misfolded proteins that are essential under stress.
Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann Herder Strasse 7, D-79104 Freiburg, Germany.
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Hesterkamp
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Bukau
D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005816:Genetic Complementation Test; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018869:Heat-Shock Response; D018832:Molecular Chaperones; D017510:Protein Folding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; C085650:hscA protein, E coli; C063842:dnaK protein, E coli