Hainzl Otmar, Wegele Harald, Richter Klaus, Buchner Johannes
Institut für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany.
J Biol Chem. 2004 May 28;279(22):23267-73. doi: 10.1074/jbc.M402189200. Epub 2004 Mar 25.
Hsp90 is a key mediator in the folding process of a growing number of client proteins. The molecular chaperone cooperates with many co-chaperones and partner proteins to fulfill its task. In Saccharomyces cerevisiae, several co-chaperones of Hsp90 interact with Hsp90 via a tetratricopeptide repeat (TPR) domain. Here we show that one of these proteins, Cns1, binds both to Hsp90 and to the yeast Hsp70 protein Ssa1 with comparable affinities. This is reminiscent of Sti1, another TPR-containing co-chaperone. Unlike Sti1, Cns1 exhibits no influence on the ATPase of Hsp90. However, it activates the ATPase of Ssa1 up to 30-fold by accelerating the rate-limiting ATP hydrolysis step. This stimulating effect is mediated by the N-terminal TPR-containing part of Cns1, whereas the C-terminal part showed no effect. Competition experiments allow the conclusion that Hsp90 and Ssa1 compete for binding to the single TPR domain of Cns1. Taken together, Cns1 is a potent cochaperone of Ssa1. Our findings highlight the importance of the regulation of Hsp70 function in the context of the Hsp90 chaperone cycle.
热休克蛋白90（Hsp90）是越来越多客户蛋白折叠过程中的关键介质。这种分子伴侣与许多共伴侣和伙伴蛋白协同作用以完成其任务。在酿酒酵母中，Hsp90的几种共伴侣通过四肽重复（TPR）结构域与Hsp90相互作用。在这里，我们表明这些蛋白之一Cns1以相当的亲和力同时结合Hsp90和酵母热休克蛋白70（Hsp70）蛋白Ssa1。这让人联想到另一种含TPR的共伴侣Sti1。与Sti1不同，Cns1对Hsp90的ATP酶没有影响。然而，它通过加速限速ATP水解步骤将Ssa1的ATP酶激活高达30倍。这种刺激作用由Cns1含N端TPR的部分介导，而C端部分则没有作用。竞争实验得出的结论是，Hsp90和Ssa1竞争与Cns1的单个TPR结构域结合。综上所述，Cns1是Ssa1的一种有效的共伴侣。我们的研究结果突出了在Hsp90伴侣循环背景下Hsp70功能调节的重要性。
