PDF(Pubmed)
Abstract：
The anion exchanger solute carrier family 26 (SLC26)A9, consisting of the transmembrane (TM) domain and the cytoplasmic STAS domain, plays an essential role in regulating chloride transport across cell membranes. Recent studies have indicated that C-terminal helices block the entrance of the putative ion transport pathway. However, the precise functions of the STAS domain and C-terminal helix, as well as the underlying molecular mechanisms governing the transport process, remain poorly understood. In this study, we performed molecular dynamics simulations of three distinct models of human SLC26A9, full-length, STAS domain removal (ΔSTAS), and C-terminus removal (ΔC), to investigate their conformational dynamics and ion-binding properties. Stable binding of ions to the binding sites was exclusively observed in the ΔC model in these simulations. Comparing the full-length and ΔC simulations, the ΔC model displayed enhanced motion of the STAS domain. Furthermore, comparing the ΔSTAS and ΔC simulations, the ΔSTAS simulation failed to exhibit stable ion bindings to the sites despite the absence of the C-terminus blocking the ion transmission pathway in both systems. These results suggest that the removal of the C-terminus not only unblocks the access of ions to the permeation pathway but also triggers STAS domain motion, gating the TM domain to promote ions\' entry into their binding site. Further analysis revealed that the asymmetric motion of the STAS domain leads to the expansion of the ion permeation pathway within the TM domain, resulting in the stiffening of the flexible TM12 helix near the ion-binding site. This structural change in the TM12 helix stabilizes chloride ion binding, which is essential for SLC26A9\'s alternate-access mechanism. Overall, our study provides new insights into the molecular mechanisms of SLC26A9 transport and may pave the way for the development of novel treatments for diseases associated with dysregulated ion transport.
摘要：
阴离子交换剂SLC26A9，由跨膜（TM）结构域和胞质STAS结构域组成，在调节氯化物跨细胞膜的运输中起着至关重要的作用。最近的研究表明，C末端螺旋阻断了假定的离子转运途径的入口。然而,STAS结构域和C端螺旋的精确功能，以及控制运输过程的潜在分子机制，仍然知之甚少。在这项研究中,我们对人类SLC26A9的三种不同模型进行了分子动力学模拟：全长（FL），STAS域移除(ΔSTAS)，和C末端去除(ΔC)，研究其构象动力学和离子结合特性。在这些模拟中,在ΔC模型中仅观察到离子与结合位点的稳定结合。比较FL和ΔC模拟，ΔC模型显示了STAS域的增强运动。此外，比较ΔSTAS和ΔC模拟，尽管两个系统中都没有C末端阻断离子传输途径，但ΔSTAS模拟未能显示出稳定的离子结合位点。这些结果表明，C末端的去除不仅可以阻断离子进入渗透途径，还可以触发STAS结构域运动。门控TM域以促进离子进入其结合位点。进一步的分析表明，STAS域的非对称运动导致TM域内离子渗透途径的扩展，导致离子结合位点附近的柔性TM12螺旋变硬。TM12螺旋的这种结构变化稳定了氯离子的结合，这对于SLC26A9的备用访问机制至关重要。总的来说,我们的研究为SLC26A9转运的分子机制提供了新的见解，并可能为开发与离子转运失调相关的疾病的新疗法铺平道路。
