Srivastava Shubhra, Miranda Pablo, Giraldez Teresa, Zhu Jianghai, Cachau Raul E, Holmgren Miguel
Molecular Neurophysiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States.
Institute of Biomedical Technologies & Department Basic Medical Sciences, School of Medicine, University of La Laguna, Tenerife, Spain.
Front Mol Biosci. 2024 Sep 17;11:1454273. doi: 10.3389/fmolb.2024.1454273. eCollection 2024.
We studied the impact of Ba ions on the function and structure of large conductance potassium (BK) channels. Ion composition has played a crucial role in the physiological studies of BK channels due to their ability to couple ion composition and membrane voltage signaling. Unlike Ca, which activates BK channels through all (RCK) domains, Ba has been described as specifically interacting with the RCK2 domain. It has been shown that Ba also blocks potassium permeation by binding to the channel's selectivity filter. The Cryo-EM structure of the BK channel in the presence of high concentration Ba here presented (PDBID: 7RJT) revealed that Ba occupies the K S3 site in the selectivity filter. Densities attributed to K ions were observed at sites S2 and S4. Ba ions were also found bound to the high-affinity Ca binding sites RCK1 and RCK2, which agrees with functional work suggesting that the Ba increases open probability through the Ca bowl site (RCK2). A comparative analysis with a second structure here presented (PDBID: 7RK6), obtained without additional Ba, shows localized changes between the RCK1 and RCK2 domains, suggestive of coordinated dynamics between the RCK ion binding sites with possible relevance for the activation/blockade of the channel. The observed densities attributed to Ba at RCK1 and RCK2 sites and the selectivity filter contribute to a deeper understanding of the structural basis for Ba's dual role in BK channel modulation, adding to the existing knowledge in this field.
我们研究了钡离子对大电导钾（BK）通道功能和结构的影响。离子组成在BK通道的生理学研究中发挥了关键作用，因为它们能够将离子组成与膜电压信号传导联系起来。与通过所有（RCK）结构域激活BK通道的钙不同，钡已被描述为特异性地与RCK2结构域相互作用。研究表明，钡还通过与通道的选择性过滤器结合来阻断钾离子渗透。此处展示的高浓度钡存在下BK通道的冷冻电镜结构（PDBID：7RJT）显示，钡占据了选择性过滤器中的钾S3位点。在S2和S4位点观察到了归因于钾离子的密度。还发现钡离子与高亲和力钙结合位点RCK1和RCK2结合，这与功能研究结果一致，即钡通过钙碗位点（RCK2）增加开放概率。此处展示的与另一个无额外钡的结构（PDBID：7RK6）的比较分析表明，RCK1和RCK2结构域之间存在局部变化，这表明RCK离子结合位点之间存在协同动力学，可能与通道的激活/阻断有关。在RCK1和RCK2位点以及选择性过滤器处观察到的归因于钡的密度有助于更深入地理解钡在BK通道调节中双重作用的结构基础，丰富了该领域的现有知识。
