The 90-kDa heat shock protein (hsp-90) possesses an ATP binding site and autophosphorylating activity.
The 90-kDa heat shock protein (hsp-90) is an abundant cytosolic protein believed to play a role in maintenance of protein trafficking and closely associated with several steroid hormone receptors. Incubation of highly purified hsp-90 with [gamma-32P]ATP results in its autophosphorylation on serine residues. There are several lines of evidence which suggest that this activity is due to a kinase intrinsic to hsp-90 rather than some closely associated protein kinases: 1) the phosphorylation persists after the removal of casein kinase II by heparin chromatography and after immunoprecipitation of hsp-90 with anti-hsp-90 antibodies. 2) The approximate kM for ATP of the reaction is 0.16 mM, higher than that of many other protein kinases. 3) Phosphorylation is not affected by a number of activators and inhibitors of other known kinases which might associate with hsp-90. 4) The phosphorylation displays a unique cation dependence being most active in the presence of Ca2+ and practically inactive with Mg2+, although the autophosphorylation in the presence of Mg2+ is activated by histones and polyamines. 5) The activity is remarkably heat-stable; incubation of hsp-90 for 20 min at 95 degrees C results in only a 60% decrease in autophosphorylation. 6) Finally, and most importantly, purified hsp-90 can be labeled with azido-ATP and it is able to bind to ATP-agarose. The binding shows similar cation dependence to the autophosphorylation. These data are in agreement with the presence of a consensus sequence for ATP binding sites in the primary structure of the protein similar to that observed in the 70-kDa heat-shock proteins. Our data suggest the 90-kDa heat shock protein possesses an enzymatic activity analogous in many respects to the similar activity of the 70-kDa heat shock proteins. This may represent an important, previously unrecognized function of hsp-90.
Csermely
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Research Division, Joslin Diabetes Center, Boston, Massachusetts.
Kahn
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CR
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002413:Cations, Divalent; D004591:Electrophoresis, Polyacrylamide Gel; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains
D000596:Amino Acids; D002413:Cations, Divalent; D006360:Heat-Shock Proteins; D000255:Adenosine Triphosphate