Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA, 94143, USA.
Novartis Institutes for BioMedical Research, San Diego, CA, 92121, USA.
Nat Commun. 2023 Apr 17;14(1):2197. doi: 10.1038/s41467-023-37659-7.
The Hsp90 molecular chaperone collaborates with the phosphorylated Cdc37 cochaperone for the folding and activation of its many client kinases. As with many kinases, the Hsp90 client kinase CRaf is activated by phosphorylation at specific regulatory sites. The cochaperone phosphatase PP5 dephosphorylates CRaf and Cdc37 in an Hsp90-dependent manner. Although dephosphorylating Cdc37 has been proposed as a mechanism for releasing Hsp90-bound kinases, here we show that Hsp90 bound kinases sterically inhibit Cdc37 dephosphorylation indicating kinase release must occur before Cdc37 dephosphorylation. Our cryo-EM structure of PP5 in complex with Hsp90:Cdc37:CRaf reveals how Hsp90 both activates PP5 and scaffolds its association with the bound CRaf to dephosphorylate phosphorylation sites neighboring the kinase domain. Thus, we directly show how Hsp90's role in maintaining protein homeostasis goes beyond folding and activation to include post translationally modifying its client kinases.
Hsp90 分子伴侣与磷酸化的 Cdc37 共伴侣合作，帮助其众多客户激酶折叠和激活。与许多激酶一样，Hsp90 客户激酶 CRaf 通过特定调节位点的磷酸化而被激活。共伴侣磷酸酶 PP5 以依赖 Hsp90 的方式去磷酸化 CRaf 和 Cdc37。虽然去磷酸化 Cdc37 被提出作为释放 Hsp90 结合激酶的一种机制，但在这里我们表明，Hsp90 结合的激酶在空间位阻上抑制 Cdc37 的去磷酸化，这表明激酶的释放必须发生在 Cdc37 去磷酸化之前。我们的 PP5 与 Hsp90:Cdc37:CRaf 复合物的冷冻电镜结构揭示了 Hsp90 如何既能激活 PP5，又能将其与结合的 CRaf 支架在一起，以去磷酸化靠近激酶结构域的磷酸化位点。因此，我们直接展示了 Hsp90 在维持蛋白质内稳性方面的作用如何超出了折叠和激活，包括对其客户激酶进行翻译后修饰。
