The endoplasmic reticulum (ER) chaperones BiP and Grp94 selectively associate when BiP is in the ADP conformation.
The endoplasmic reticulum (ER) chaperones BiP and Grp94 selectively associate when BiP is in the ADP conformation.
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当 BiP 处于 ADP 构象时，内质网 (ER) 伴侣 BiP 和 Grp94 选择性结合。
DOI：
10.1074/jbc.ra118.007050
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Street,TimothyO
中科院分区：
文献类型：
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作者：
Sun,Ming;Kotler,JudyLM;Liu,Shanshan;Street,TimothyO
Hsp 70和Hsp 90分子伴侣对细胞质中的蛋白质质量控制至关重要，而细胞器特异性Hsp 70/Hsp 90旁系同源物对线粒体和内质网（ER）提供类似的保护。胞质Hsp 70/Hsp 90可以顺序地操作，其中在Hsp 70与客户蛋白结合之后，Hsp 90选择性地与Hsp 70缔合。这一观察结果长期以来一直表明，Hsp 90可能倾向于在客户端折叠的后期阶段与客户端相互作用。然而，最近的工作表明，胞质Hsp 70/Hsp 90可以直接相互作用，即使在没有客户端，这开辟了一个替代的可能性，Hsp 70/Hsp 90与客户端的有序相互作用可能是一个结果，在Hsp 70和Hsp 90之间的直接相互作用的调节变化。然而，尚不清楚这种调节如何在机械上发生。在这里，我们发现ER Hsp 70/Hsp 90（BiP/Grp 94）可以在没有客户端的情况下形成直接复合物。重要的是，BiP和Grp 94之间的直接相互作用是核苷酸特异性的，BiP和Grp 94在ADP条件下具有较高的亲和力，而在ATP条件下具有较低的亲和力。我们发现，这种核苷酸特异性的关联之间的BiP和Grp 94在很大程度上是由于BiP的构象。当BiP处于ATP构象时，其底物结合结构域阻断Grp 94;相反，Grp 94可以容易地与BiP的ADP构象缔合，这代表BiP的客户端结合状态。我们的观察结果提供了一种机制，BiP和Grp 94顺序参与客户端折叠，其中BiP的构象提供了随后招募Grp 94的信号。
Hsp70 and Hsp90 chaperones are critical for protein quality control in the cytosol, whereas organelle-specific Hsp70/Hsp90 paralogs provide similar protection for mitochondria and the endoplasmic reticulum (ER). Cytosolic Hsp70/Hsp90 can operate sequentially with Hsp90 selectively associating with Hsp70 after Hsp70 is bound to a client protein. This observation has long suggested that Hsp90 could have a preference for interacting with clients at their later stages of folding. However, recent work has shown that cytosolic Hsp70/Hsp90 can directly interact even in the absence of a client, which opens up an alternative possibility that the ordered interactions of Hsp70/Hsp90 with clients could be a consequence of regulated changes in the direct interactions between Hsp70 and Hsp90. However, it is unknown how such regulation could occur mechanistically. Here, we find that the ER Hsp70/Hsp90 (BiP/Grp94) can form a direct complex in the absence of a client. Importantly, the direct interaction between BiP and Grp94 is nucleotide-specific, with BiP and Grp94 having higher affinity under ADP conditions and lower affinity under ATP conditions. We show that this nucleotide-specific association between BiP and Grp94 is largely due to the conformation of BiP. When BiP is in the ATP conformation its substrate-binding domain blocks Grp94; in contrast, Grp94 can readily associate with the ADP conformation of BiP, which represents the client-bound state of BiP. Our observations provide a mechanism for the sequential involvement of BiP and Grp94 in client folding where the conformation of BiP provides the signal for the subsequent recruitment of Grp94.