Post-translational modifications of Hsp90

2018年，(1)我们报道了酵母中一个在多细胞真核生物中不保守的Hsp90辅助伴侣在功能上被人类细胞中特异的翻译后修饰所取代。具体地说，人Hsp90α中高度保守的酪氨酸627的磷酸化导致伴侣蛋白的远程构象变化，导致Hsp90 N结构域的二聚化丧失。虽然酵母Hsp90中的酪氨酸627没有被磷酸化，但它的拟磷突变对酵母Hsp90构象的影响与人Hsp90α中非保守的酵母辅助伴侣Hch1的过度表达和酪氨酸627的磷酸化相似。我们的数据与这种翻译后修饰出现在高等真核生物中代表Hch1蛋白的进化替代的可能性是一致的。(2)我们发现，磷酸化诱导的Hsp90辅伴蛋白CDC37的去折叠促进了激酶向Hsp90的募集和客户类特异性的Hsp90磷酸化。在Hsp90介导的蛋白激酶伴侣过程中，该机制的核心组件Hsp90和辅酶伴侣CDC37在不同的磷酸化状态之间循环，调节伴侣蛋白循环的进程。我们发现Y298位的CDC37磷酸化导致C-末端结构域的部分展开和折叠中间产物的数量。去折叠通过揭示一个磷酸肽序列来促进Hsp90在Y197的磷酸化，该序列作为一个对接位置，通过它们的SH2结构域将非受体酪氨酸激酶招募到伴侣复合体中。反过来，Y197处的Hsp90磷酸化特异性地调节其与CDC37的相互作用，从而仅影响蛋白激酶客户的伴侣。总之，我们发现，通过提供客户类特异性，Hsp90辅伴子，如CDC37，不仅有助于客户招募，而且还以客户类特定的方式塑造了Hsp90的翻译后修改图景。最近，我们发表了Hsp90中间结构域特定酪氨酸残基的磷酸化通过诱导Hsp90独特的可逆构象来显著增强刺激性辅助伴侣AHA1的结合。

In 2018, (1) we reported that an Hsp90 co-chaperone in yeast that is not conserved in multi-cellular eukaryotes is functionally replaced by site-specific postranslational modification in human cells. Specifically, phosphorylation of the highly conserved tyrosine 627 in human Hsp90 alpha causes a long-range conformational change in the chaperone resulting in loss of dimerization of the Hsp90 N-domains. Although tyrosine 627 in yeast Hsp90 is not phosphorylated its phosphomimetic mutation has a similar effect on yeast Hsp90 conformation as does over-expression of the non-conserved yeast co-chaperone Hch1 and phosphorylation of tyrosine 627 in human Hsp90 alpha. Our data are consistent with the possibility that appearance of this posttranslational modification in higher eukaryotes represents an evolutionary substitution for Hch1 protein. (2) We showed that phosphorylation-induced unfolding of the Hsp90 co-chaperone Cdc37 promotes kinase recruitment to Hsp90 and client class-specific Hsp90 phosphorylation. During the Hsp90-mediated chaperoning of protein kinases, the core components of the machinery, Hsp90 and the cochaperone Cdc37, recycle between different phosphorylation states that regulate progression of the chaperone cycle. We show that Cdc37 phosphorylation at Y298 results in partial unfolding of the C-terminal domain and the population of folding intermediates. Unfolding facilitates Hsp90 phosphorylation at Y197 by unmasking a phosphopeptide sequence, which serves as a docking site to recruit non-receptor tyrosine kinases to the chaperone complex via their SH2 domains. In turn, Hsp90 phosphorylation at Y197 specifically regulates its interaction with Cdc37 and thus affects the chaperoning of only protein kinase clients. In summary, we find that by providing client class specificity, Hsp90 cochaperones such as Cdc37 do not merely assist in client recruitment but also shape the post-translational modification landscape of Hsp90 in a client class-specific manner. Most recently, we have published that phosphorylation of a specific tyrosine residue in the middle domain of Hsp90 dramatically enhances association of the stimulatory co-chaperone Aha1 by inducing a unique and reversible conformation of Hsp90.