The Intracellular Loop of the Na + /Ca 2+ Exchanger Contains an “Awareness Ribbon”-Shaped Two-Helix Bundle Domain
The Intracellular Loop of the Na + /Ca 2+ Exchanger Contains an “Awareness Ribbon”-Shaped Two-Helix Bundle Domain
复制标题
Na /Ca 2 交换器的细胞内环包含“意识带”形双螺旋束结构域
DOI：
10.1021/acs.biochem.8b00300
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发表时间：
2018
期刊：
影响因子：
2.9
通讯作者：
Brüschweiler, Rafael
中科院分区：
文献类型：
--
作者：
Yuan, Jiaqi;Yuan, Chunhua;Xie, Mouzhe;Yu, Lei;Bruschweiler-Li, Lei;Brüschweiler, Rafael
Na+/Ca~(2+)交换器(NCX)是一种普遍存在的单链膜蛋白，通过Na~+和Ca~(2+)跨细胞膜的反向转运，在调节细胞内Ca~(2+)动态平衡中发挥重要作用。与原核蛋白不同，NCX蛋白只含有跨膜区，是一种自给自足的活性离子转运蛋白，它还具有一个大的胞内环路，可以感知细胞内的钙信号，并控制跨膜离子转运的激活。这为真核细胞更复杂的功能提供了必要的调节层。细胞内环中的钙感受器称为钙结合结构域(CBD12)。然而，变构细胞内钙结合的信号是如何传播并导致跨膜离子转运的，目前还缺乏详细的解释。因此，对CBD12两侧的细胞内环进行进一步的结构和动力学表征是当务之急。在这里，我们报告了使用溶液核磁共振(NMR)光谱识别和表征细胞内环中CBD12的N端的另一个结构域。该结构域的原子结构表明，两个串联的长α-螺旋由一个短连接子连接，形成一个稳定的交叉两螺旋束，类似于一条“感知带”。考虑到THB结构域的高度保守的氨基酸序列，THB结构域的详细结构和动力学特性在不同物种的NCX中是共同的，这将有助于理解真核生物Na+/Ca~(2+)交换的调节机制。
The Na+/Ca2+exchanger (NCX) is a ubiquitous single-chain membrane protein that plays a major role in regulating the intracellular Ca2+homeostasis by the counter transport of Na+and Ca2+across the cell membrane. Other than its prokaryotic counterpart, which contains only the transmembrane domain and is self-sufficient as an active ion transporter, the eukaryotic NCX protein possesses in addition a large intracellular loop that senses intracellular calcium signals and controls the activation of ion transport across the membrane. This provides a necessary layer of regulation for the more complex function of eukaryotic cells. The Ca2+sensor in the intracellular loop is known as the Ca2+-binding domain (CBD12). However, how the signaling of the allosteric intracellular Ca2+binding propagates and results in transmembrane ion transportation still lacks a detailed explanation. Further structural and dynamics characterization of the intracellular loop flanking both sides of CBD12 is therefore imperative. Here, we report the identification and characterization of another structured domain that is N-terminal to CBD12 in the intracellular loop using solution nuclear magnetic resonance (NMR) spectroscopy. The atomistic structure of this domain reveals that two tandem long α-helices, connected by a short linker, form a stable crossover two-helix bundle (THB), resembling an “awareness ribbon”. Considering the highly conserved amino acid sequence of the THB domain, the detailed structural and dynamics properties of the THB domain will be common among NCXs from different species and will contribute toward the understanding of the regulatory mechanism of eukaryotic Na+/Ca2+exchangers.