Liberek K, Marszalek J, Ang D, Georgopoulos C, Zylicz M
Department of Molecular Biology, University of Gdansk, Poland.
Proc Natl Acad Sci U S A. 1991 Apr 1;88(7):2874-8. doi: 10.1073/pnas.88.7.2874.
The products of the Escherichia coli dnaK, dnaJ, and grpE heat shock genes have been previously shown to be essential for bacteriophage lambda DNA replication at all temperatures and for bacterial survival under certain conditions. DnaK, the bacterial heat shock protein hsp70 analogue and putative chaperonin, possesses a weak ATPase activity. Previous work has shown that ATP hydrolysis allows the release of various polypeptides complexed with DnaK. Here we demonstrate that the ATPase activity of DnaK can be greatly stimulated, up to 50-fold, in the simultaneous presence of the DnaJ and GrpE heat shock proteins. The presence of either DnaJ or GrpE alone results in a slight stimulation of the ATPase activity of DnaK. The action of the DnaJ and GrpE proteins may be sequential, since the presence of DnaJ alone leads to an acceleration in the rate of hydrolysis of the DnaK-bound ATP. The presence of GrpE alone increases the rate of release of bound ATP or ADP without affecting the rate of hydrolysis. The stimulation of the ATPase activity of DnaK may contribute to its more efficient recycling, and it helps explain why mutations in dnaK, dnaJ, or grpE genes often exhibit similar pleiotropic phenotypes.
先前的研究表明，大肠杆菌dnaK、dnaJ和grpE热休克基因的产物对于噬菌体λ DNA在所有温度下的复制以及细菌在某些条件下的存活至关重要。DnaK是细菌热休克蛋白hsp70的类似物，被认为是伴侣蛋白，具有较弱的ATP酶活性。先前的研究表明，ATP水解能使与DnaK结合的各种多肽释放出来。在此我们证明，在同时存在DnaJ和GrpE热休克蛋白的情况下，DnaK的ATP酶活性可被极大地刺激，提高达50倍。单独存在DnaJ或GrpE时，会使DnaK的ATP酶活性稍有刺激。DnaJ和GrpE蛋白的作用可能是相继发生的，因为单独存在DnaJ会导致DnaK结合的ATP水解速率加快。单独存在GrpE会增加结合的ATP或ADP的释放速率，而不影响水解速率。DnaK的ATP酶活性的刺激可能有助于其更有效地循环利用，这也有助于解释为什么dnaK、dnaJ或grpE基因中的突变常常表现出相似的多效性表型。
