Brychzy Alexander, Rein Theo, Winklhofer Konstanze F, Hartl F Ulrich, Young Jason C, Obermann Wolfgang M J
Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18a, D-82152 Martinsried, Germany.
EMBO J. 2003 Jul 15;22(14):3613-23. doi: 10.1093/emboj/cdg362.
In the eukaryotic cytosol, Hsp70 and Hsp90 cooperate with various co-chaperone proteins in the folding of a growing set of substrates, including the glucocorticoid receptor (GR). Here, we analyse the function of the co-chaperone Tpr2, which contains two chaperone-binding TPR domains and a DnaJ homologous J domain. In vivo, an increase or decrease in Tpr2 expression reduces GR activation, suggesting that Tpr2 is required at a narrowly defined expression level. As shown in vitro, Tpr2 recognizes both Hsp70 and Hsp90 through its TPR domains, and its J domain stimulates ATP hydrolysis and polypeptide binding by Hsp70. Furthermore, unlike other co-chaperones, Tpr2 induces ATP-independent dissociation of Hsp90 but not of Hsp70 from chaperone-substrate complexes. Excess Tpr2 inhibits the Hsp90-dependent folding of GR in cell lysates. We propose a novel mechanism in which Tpr2 mediates the retrograde transfer of substrates from Hsp90 onto Hsp70. At normal levels substoichiometric to Hsp90 and Hsp70, this activity optimizes the function of the multichaperone machinery.
在真核细胞溶质中，Hsp70和Hsp90与多种共伴侣蛋白协同作用，参与一系列不断增加的底物的折叠过程，其中包括糖皮质激素受体（GR）。在此，我们分析了共伴侣蛋白Tpr2的功能，它包含两个与伴侣蛋白结合的TPR结构域和一个与DnaJ同源的J结构域。在体内，Tpr2表达的增加或减少都会降低GR的激活，这表明Tpr2在一个狭窄的特定表达水平上是必需的。如体外实验所示，Tpr2通过其TPR结构域识别Hsp70和Hsp90，并且其J结构域能刺激Hsp70的ATP水解和多肽结合。此外，与其他共伴侣蛋白不同，Tpr2能诱导Hsp90从伴侣蛋白 - 底物复合物中发生不依赖ATP的解离，但不会诱导Hsp70发生这种解离。过量的Tpr2会抑制细胞裂解物中GR的Hsp90依赖性折叠。我们提出了一种新机制，即Tpr2介导底物从Hsp90逆向转移到Hsp70上。在与Hsp90和Hsp70化学计量比不足的正常水平下，这种活性优化了多伴侣蛋白机制的功能。
