Mg2+-ATP Sensing in CNNM, a Putative Magnesium Transporter
Mg2+-ATP Sensing in CNNM, a Putative Magnesium Transporter
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DOI：
10.1016/j.str.2019.11.016
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发表时间：
2020-03-03
期刊：
影响因子：
5.7
通讯作者：
Gehring, Kalle
中科院分区：
文献类型：
--
作者：
Chen, Yu Seby;Kozlov, Guennadi;Gehring, Kalle
胱硫醚-β-合酶 (CBS) 对结构域二价金属阳离子转运介体 (CNNM) 家族由四种与 Mg2+ 转运相关的整合膜蛋白组成。在结构上，CNNM 包含由 CBS 对和环核苷酸结合同源 (CNBH) 结构域组成的大型胞质区域。它们如何调节 Mg2+ 转运活性尚不清楚。在这里，我们确定了两种构象的胞质片段的晶体结构：Mg2+-ATP-类似物结合和游离配体。这些结构揭示了开放和闭合构象，具有在各个域的结构中未观察到的功能上重要的接触。我们还在 CBS 对结构域中确定了第二个 Mg2+ 结合区域，以及 CNBH 结构域的不同二聚化界面。分析超速离心和等温滴定量热实验揭示了 Mg2+-ATP 结合与蛋白质二聚化之间的紧密相关性。阻断任一功能的突变会阻止细胞 Mg2+ 流出活性。结果表明 Mg2+ 流出受到 Mg2+-ATP 与 CNNM CBS 对结构域结合相关的构象变化的调节。
The family of cystathionine-beta-synthase (CBS)-pair domain divalent metal cation transport mediators (CNNMs) is composed of four integral membrane proteins associated with Mg2+ transport. Structurally, CNNMs contain large cytosolic regions composed of a CBS-pair and a cyclic nucleotide-binding homology (CNBH) domain. How these regulate Mg2+ transport activity is unknown. Here, we determined the crystal structures of cytosolic fragments in two conformations: Mg2+-ATP-analog bound and ligand free. The structures reveal open and closed conformations with functionally important contacts not observed in structures of the individual domains. We also identified a second Mg2+-binding region in the CBS-pair domain and a different dimerization interface for the CNBH domain. Analytical ultracentrifugation and isothermal titration calorimetry experiments revealed a tight correlation between Mg2+-ATP binding and protein dimerization. Mutations that blocked either function prevented cellular Mg2+ efflux activity. The results suggest Mg2+ efflux is regulated by conformational changes associated with Mg2+-ATP binding to CNNM CBS-pair domains.