Department of Environmental Toxicology, University of California, Davis, California 95616-8588, USA.
J Biol Chem. 2011 Oct 7;286(40):35275-82. doi: 10.1074/jbc.M111.246439. Epub 2011 Aug 19.
Hsp90 (heat shock protein of 90 kDa) is often found associated with functional domains of client proteins, including those for ligand binding, dimerization, DNA binding, and enzymatic activity. Although Hsp90 can maintain the conformation of functionally important domains prior to activation of the client protein, its specific binding site and the mechanism(s) of Hsp90 dissociation during activation are unknown. Here, we have identified and characterized residues involved in Hsp90 binding within the aryl hydrocarbon receptor (AhR) ligand-binding domain and demonstrate that they overlap with those involved in ligand binding. In agreement with this spatial model, ligand binding results in Hsp90 dissociation from the AhR Per-ARNT-Sim B fragment. Interestingly, whereas Hsp90-binding residues within the ligand-binding domain were not involved in Hsp90-dependent AhR protein stability, several of these residues are important for ligand-dependent AhR activation, and their mutation resulted in conversion of two AhR antagonists/partial agonists into full AhR agonists. These studies reveal co-localization of a tentative Hsp90-binding site with that for AhR ligand binding and provide the first molecular mechanism for Hsp90 dissociation in the activation of a client protein.
热休克蛋白 90（Hsp90）通常与客户蛋白的功能域相关联，包括配体结合、二聚化、DNA 结合和酶活性的功能域。虽然 Hsp90 可以在客户蛋白激活之前维持功能重要域的构象，但它的特定结合位点和在激活过程中 Hsp90 解离的机制尚不清楚。在这里，我们已经鉴定和表征了芳烃受体（AhR）配体结合域中与 Hsp90 结合相关的残基，并证明它们与配体结合相关的残基重叠。与该空间模型一致，配体结合导致 Hsp90 从 AhR Per-ARNT-Sim B 片段中解离。有趣的是，尽管配体结合域中的 Hsp90 结合残基不参与 Hsp90 依赖性 AhR 蛋白稳定性，但这些残基中的几个对于配体依赖性 AhR 激活很重要，其突变将两个 AhR 拮抗剂/部分激动剂转化为完全 AhR 激动剂。这些研究揭示了暂定的 Hsp90 结合位点与 AhR 配体结合位点的共定位，并为客户蛋白激活过程中 Hsp90 解离提供了第一个分子机制。
