Calcium binding to a remote site can replace magnesium as cofactor for mitochondrial Hsp90 (TRAP1) ATPase activity.
Calcium binding to a remote site can replace magnesium as cofactor for mitochondrial Hsp90 (TRAP1) ATPase activity.
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DOI：
10.1074/jbc.ra118.003562
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发表时间：
2018-08-31
期刊：
影响因子：
--
通讯作者：
Agard DA
中科院分区：
文献类型：
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作者：
Elnatan D;Agard DA
Hsp90分子伴侣是一种依赖于三磷酸腺苷的酶，它维持蛋白质的动态平衡并调节许多重要的细胞过程。高等真核生物具有细胞器特异性的Hsp90类似物，它们适应于每个亚细胞环境。线粒体Hsp90，即肿瘤坏死因子受体相关蛋白1(TRAP1)，支持电子传递元件的折叠和活性，在线粒体信号转导中发挥重要作用。众所周知，钙在线粒体中起着重要的调节作用，在线粒体中积累的钙浓度比细胞质中的浓度高得多。令人惊讶的是，我们在这里发现钙可以取代镁，镁是必需的酶辅助因子，以支持TRAP1 ATPase的活性。异常X射线衍射实验表明，TRAP1核苷酸结合口袋中有一个钙结合部位，位于三磷酸腺苷α-磷酸附近，与β-和γ-磷酸附近的镁结合部位完全不同。在镁的存在下，与其他Hsp90一样，TRAP1对ATP的水解是非协同的，而钙结合导致Hsp90二聚体中的两个前体协同水解。结构数据表明了这种合作行为的机制。由于这种协同作用，在较高的ATP浓度下，ATPase活性随钙浓度的升高而升高，而在低浓度时则相反。结合这些观察结果，我们提出了一个模型，在该模型中，二价阳离子的选择可以控制非合作和合作的TRAP1 ATPase机制之间的切换，以响应不同的ATP浓度。这种转换可能通过改变TRAP1-ATP驱动的循环及其对不同线粒体客户的影响来促进细胞能学、线粒体信号和蛋白质动态平衡之间的协调。
The Hsp90 molecular chaperones are ATP-dependent enzymes that maintain protein homeostasis and regulate many essential cellular processes. Higher eukaryotes have organelle-specific Hsp90 paralogs that are adapted to each subcellular environment. The mitochondrial Hsp90, TNF receptor–associated protein 1 (TRAP1), supports the folding and activity of electron transport components and is increasingly appreciated as a critical player in mitochondrial signaling. Calcium plays a well-known and important regulatory role in mitochondria where it can accumulate to much higher concentrations than in the cytoplasm. Surprisingly, we found here that calcium can replace magnesium, the essential enzymatic cofactor, to support TRAP1 ATPase activity. Anomalous X-ray diffraction experiments revealed a calcium-binding site within the TRAP1 nucleotide-binding pocket located near the ATP α-phosphate and completely distinct from the magnesium-binding site adjacent to the β- and γ-phosphates. In the presence of magnesium, ATP hydrolysis by TRAP1, as with other Hsp90s, was noncooperative, whereas calcium binding resulted in cooperative hydrolysis by the two protomers within the Hsp90 dimer. The structural data suggested a mechanism for this cooperative behavior. Because of the cooperativity, at high ATP concentrations, ATPase activity was higher with calcium, whereas the converse was observed at low ATP concentrations. Integrating these observations, we propose a model in which the divalent cation choice can control switching between noncooperative and cooperative TRAP1 ATPase mechanisms in response to varying ATP concentrations. This switching may facilitate coordination between cellular energetics, mitochondrial signaling, and protein homeostasis via alterations in the TRAP1 ATP-driven cycle and its consequent effects on different mitochondrial clients.