title: Control of the DnaK chaperone cycle by substoichiometric concentrations of the co-chaperones DnaJ and GrpE.
abstract: The polypeptide binding and release cycle of the molecular chaperone DnaK (Hsp70) of Escherichia coli is regulated by the two co-chaperones DnaJ and GrpE. Here, we show that the DnaJ-triggered conversion of DnaK.ATP (T state) to DnaK.ADP.Pi (R state), as monitored by intrinsic protein fluorescence, is monophasic and occurs simultaneously with ATP hydrolysis. This is in contrast with the T-->R conversion in the absence of DnaJ which is biphasic, the first phase occurring simultaneously with the hydrolysis of ATP (Theyssen, H., Schuster, H.-P., Packschies, L., Bukau, B., and Reinstein, J. (1996) J. Mol. Biol. 263, 657-670). Apparently, DnaJ not only stimulates ATP hydrolysis but also couples it with conformational changes of DnaK. In the absence of GrpE, DnaJ forms a tight ternary complex with peptide.DnaK.ADP.Pi (Kd = 0.14 microM). However, by monitoring complex formation between DnaK (1 microM) and a fluorophore-labeled peptide in the presence of ATP (1 mM), DnaJ (1 microM), and varying concentrations of the ADP/ATP exchange factor GrpE (0.1-3 microM), substoichiometric concentrations of GrpE were found to shift the equilibrium from the slowly binding and releasing, high-affinity R state of DnaK completely to the fast binding and releasing, low-affinity T state and thus to prevent the formation of a long lived ternary DnaJ. substrate.DnaK.ADP.Pi complex. Under in vivo conditions with an estimated chaperone ratio of DnaK:DnaJ:GrpE = 10:1:3, both DnaJ and GrpE appear to control the chaperone cycle by transient interactions with DnaK.
authors.affiliation: Biochemisches Institut, Universität Zürich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland.
authors.forename: E V
authors.initials: EV
authors.lastname: Pierpaoli
authors.forename: E
authors.initials: E
authors.lastname: Sandmeier
authors.forename: H J
authors.initials: HJ
authors.lastname: Schönfeld
authors.forename: P
authors.initials: P
authors.lastname: Christen
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D018832:Molecular Chaperones
chemical_list: D001426:Bacterial Proteins; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; C068113:GrpE protein, Bacteria; C489400:GrpE protein, E coli; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D000255:Adenosine Triphosphate; C063842:dnaK protein, E coli