Department of Pharmacology and Toxicology, Faculty of Biology and Medicine, University of Lausanne, 1011 Lausanne, Switzerland.
SIB (Swiss Institute of Bioinformatics), Biozentrum, University of Basel, 4056 Basel, Switzerland.
Proc Natl Acad Sci U S A. 2017 Apr 4;114(14):3768-3773. doi: 10.1073/pnas.1620560114. Epub 2017 Mar 20.
Acid-sensing ion channels (ASICs) are proton-activated Na channels expressed in the nervous system, where they are involved in learning, fear behaviors, neurodegeneration, and pain sensation. In this work, we study the role in pH sensing of two regions of the ectodomain enriched in acidic residues: the acidic pocket, which faces the outside of the protein and is the binding site of several animal toxins, and the palm, a central channel domain. Using voltage clamp fluorometry, we find that the acidic pocket undergoes conformational changes during both activation and desensitization. Concurrently, we find that, although proton sensing in the acidic pocket is not required for channel function, it does contribute to both activation and desensitization. Furthermore, protonation-mimicking mutations of acidic residues in the palm induce a dramatic acceleration of desensitization followed by the appearance of a sustained current. In summary, this work describes the roles of potential pH sensors in two extracellular domains, and it proposes a model of acidification-induced conformational changes occurring in the acidic pocket of ASIC1a.
酸敏离子通道（ASICs）是一种在神经系统中表达的质子激活的 Na+通道，在学习、恐惧行为、神经退行性变和痛觉感知中发挥作用。在这项工作中，我们研究了富含酸性残基的两个胞外域在 pH 感应中的作用：酸性口袋，它面向蛋白质的外部，是几种动物毒素的结合位点，以及手掌，一个中央通道域。我们使用电压钳荧光法发现，在激活和脱敏过程中，酸性口袋都会发生构象变化。同时，我们发现，虽然酸性口袋中的质子感应对于通道功能不是必需的，但它确实有助于激活和脱敏。此外，手掌中酸性残基的质子模拟突变会导致脱敏的急剧加速，随后出现持续电流。总之，这项工作描述了两个细胞外域中潜在的 pH 传感器的作用，并提出了一个酸诱导构象变化发生在 ASIC1a 的酸性口袋中的模型。
