Department of Pharmaceutical Sciences, University of North Texas System College of Pharmacy, University of North Texas Health Science Center, Fort Worth, TX, 76107, USA.
Department of Pharmacology & Neuroscience, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX, 76107, USA.
Nat Commun. 2018 May 25;9(1):2082. doi: 10.1038/s41467-018-04424-0.
Acid-sensing ion channels (ASICs) evolved to sense changes in extracellular acidity with the divalent cation calcium (Ca) as an allosteric modulator and channel blocker. The channel-blocking activity is most apparent in ASIC3, as removing Ca results in channel opening, with the site's location remaining unresolved. Here we show that a ring of rat ASIC3 (rASIC3) glutamates (Glu435), located above the channel gate, modulates proton sensitivity and contributes to the formation of the elusive Ca block site. Mutation of this residue to glycine, the equivalent residue in chicken ASIC1, diminished the rASIC3 Ca block effect. Atomistic molecular dynamic simulations corroborate the involvement of this acidic residue in forming a high-affinity Ca site atop the channel pore. Furthermore, the reported observations provide clarity for past controversies regarding ASIC channel gating. Our findings enhance understanding of ASIC gating mechanisms and provide structural and energetic insights into this unique calcium-binding site.
酸敏离子通道 (ASICs) 的进化目的是感知细胞外酸度的变化，其中二价阳离子钙 (Ca) 作为别构调节剂和通道阻断剂。通道阻断活性在 ASIC3 中最为明显，因为去除 Ca 会导致通道开放，但其位置仍未得到解决。在这里，我们表明，位于通道门上方的大鼠 ASIC3（rASIC3）谷氨酸（Glu435）环调节质子敏感性，并有助于形成难以捉摸的 Ca 阻断位点。将该残基突变为鸡 ASIC1 中的等效残基甘氨酸，会降低 rASIC3 的 Ca 阻断效应。原子分子动力学模拟证实了这种酸性残基在通道孔顶部形成高亲和力 Ca 结合位点中的作用。此外，报告的观察结果为过去关于 ASIC 通道门控的争议提供了清晰的认识。我们的发现增强了对 ASIC 门控机制的理解，并为这个独特的钙结合位点提供了结构和能量方面的见解。
