Department of Biomedical Sciences, University of Lausanne , 1011 Lausanne, Switzerland.
Swiss Institute of Bioinformatics , 4056 Basel, Switzerland.
Open Biol. 2024 Jun;14(6):240028. doi: 10.1098/rsob.240028. Epub 2024 Jun 19.
Acid-sensing ion channels (ASICs) are neuronal Na-permeable ion channels activated by extracellular acidification. ASICs are involved in learning, fear sensing, pain sensation and neurodegeneration. Increasing the extracellular Ca concentration decreases the H sensitivity of ASIC1a, suggesting a competition for binding sites between H and Ca ions. Here, we predicted candidate residues for Ca binding on ASIC1a, based on available structural information and our molecular dynamics simulations. With functional measurements, we identified several residues in cavities previously associated with pH-dependent gating, whose mutation reduced the modulation by extracellular Ca of the ASIC1a pH dependence of activation and desensitization. This occurred likely owing to a disruption of Ca binding. Our results link one of the two predicted Ca-binding sites in each ASIC1a acidic pocket to the modulation of channel activation. Mg regulates ASICs in a similar way as does Ca. We show that Mg shares some of the binding sites with Ca. Finally, we provide evidence that some of the ASIC1a Ca-binding sites are functionally conserved in the splice variant ASIC1b. Our identification of divalent cation-binding sites in ASIC1a shows how Ca affects ASIC1a gating, elucidating a regulatory mechanism present in many ion channels.
酸敏离子通道（ASICs）是一种神经元钠离子通透性离子通道，可被细胞外酸化激活。ASICs 参与学习、恐惧感知、疼痛感知和神经退行性变。增加细胞外 Ca 浓度会降低 ASIC1a 的 H 敏感性，这表明 H 和 Ca 离子竞争结合位点。在这里，我们基于现有结构信息和分子动力学模拟，预测了 ASIC1a 上 Ca 结合的候选残基。通过功能测量，我们确定了先前与 pH 门控相关的空腔中的几个残基，其突变降低了细胞外 Ca 对 ASIC1a 激活和脱敏 pH 依赖性的调制。这可能是由于 Ca 结合的破坏所致。我们的结果将每个 ASIC1a 酸性口袋中的两个预测的 Ca 结合位点之一与通道激活的调制联系起来。Mg 以类似于 Ca 的方式调节 ASICs。我们表明 Mg 与 Ca 共享一些结合位点。最后，我们提供了证据表明，ASIC1a 中的一些 Ca 结合位点在剪接变体 ASIC1b 中具有功能保守性。我们在 ASIC1a 中鉴定出二价阳离子结合位点，说明了 Ca 如何影响 ASIC1a 的门控，阐明了许多离子通道中存在的一种调节机制。
