The Fe/S assembly protein IscU behaves as a substrate for the molecular chaperone Hsc66 from Escherichia coli.
IscU, a NifU-like Fe/S-escort protein, binds to and stimulates the ATPase activity of Hsc66, a hsp70-type molecular chaperone. We present evidence that stimulation arises from interactions of IscU with the substrate-binding site of Hsc66. IscU inhibited the ability of Hsc66 to suppress the aggregation of the denatured model substrate proteins rhodanese and citrate synthase, and calorimetric and surface plasmon resonance measurements showed that ATP destabilizes Hsc66.IscU complexes in a manner expected for hsp70-substrate complexes. Studies on the interaction of IscU with Hsc66 truncation mutants further showed that IscU does not bind the isolated ATPase domain of Hsc66 but does bind and stimulate a mutant containing the ATPase domain and substrate binding beta-sandwich subdomain. These results support a role for IscU as a substrate for Hsc66 and suggest a specialized function for Hsc66 in the assembly, stabilization, or transfer of Fe/S clusters formed on IscU.
Silberg
J J
JJ
Department of Physiology and Biophysics, University of California, Irvine, California 92697, USA.
Hoff
K G
KG
Tapley
T L
TL
Vickery
L E
LE
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D013379:Substrate Specificity
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D007506:Iron-Sulfur Proteins; C411665:IscU protein, E coli; D018832:Molecular Chaperones; C085650:hscA protein, E coli; D000251:Adenosine Triphosphatases