A Na+ leak channel cloned from Trichoplax adhaerens extends extracellular pH and Ca2+ sensing for the DEG/ENaC family close to the base of Metazoa
A Na+ leak channel cloned from Trichoplax adhaerens extends extracellular pH and Ca2+ sensing for the DEG/ENaC family close to the base of Metazoa
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DOI：
10.1074/jbc.ra119.010542
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发表时间：
2019-11-01
影响因子：
4.8
通讯作者：
Senatore, Adriano
中科院分区：
文献类型：
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作者：
Elkhatib, Wassim;Smith, Carolyn L.;Senatore, Adriano
酸敏感性离子通道属于退变蛋白/上皮钠通道（DEG/ENaC）家族，响应于细胞外质子而激活，并且被认为是后口动物所特有的。然而，对pH/质子的敏感性更普遍，其中，例如，人ENaC Na+泄漏通道被增强，小鼠BASIC和秀丽隐杆线虫ACD-1 Na+泄漏通道被细胞外质子阻断。对于许多DEG/ENaC通道，细胞外Ca 2+离子调节门控，并且在某些情况下，质子和Ca 2+的结合是相互依赖的。在这里，我们功能上的特点DEG/ENaC通道从早期发散的动物粘毛藻，TadNaC 6，进行Na+-选择性泄漏电流在体外敏感的细胞外质子和Ca 2+封锁。我们确定，质子阻断增强在低外部Ca 2+浓度，而钙阻断增强在低外部质子浓度，这两个配体的竞争性结合的通道蛋白的细胞外位点的指示。TadNaC 6在其他DEG/ENaC通道中缺乏质子和Ca 2+敏感性的大多数决定性残基，并且在啮齿动物BASIC通道中与Ca 2+阻断相关的一个保守残基（S353 A）的突变反而影响质子敏感性，所有这些都表明H+和Ca 2+敏感性的独立进化。引人注目的是，TadNaC 6被一般DEG/ENaC通道阻断剂阿米洛利有效激活，这是一种罕见的功能，仅报道了酸激活通道ASIC 3。TadNaC 6的序列和结构差异，加上其非典型的功能特点，提供了独特的机会，探测质子，Ca 2+，阿米洛利调节DEG/ENaC通道和洞察祖先离子通道的可能的核心门控功能。
Acid-sensitive ion channels belonging to the degenerin/epithelial sodium channel (DEG/ENaC) family activate in response to extracellular protons and are considered unique to deuterostomes. However, sensitivity to pH/protons is more widespread, where, for example, human ENaC Na+ leak channels are potentiated and mouse BASIC and Caenorhabditis elegans ACD-1 Na+ leak channels are blocked by extracellular protons. For many DEG/ENaC channels, extracellular Ca2+ ions modulate gating, and in some cases, the binding of protons and Ca2+ is interdependent. Here, we functionally characterize a DEG/ENaC channel from the early-diverging animal Trichoplax adhaerens, TadNaC6, that conducts Na+-selective leak currents in vitro sensitive to blockade by both extracellular protons and Ca2+. We determine that proton block is enhanced in low external Ca2+ concentration, whereas calcium block is enhanced in low external proton concentration, indicative of competitive binding of these two ligands to extracellular sites of the channel protein. TadNaC6 lacks most determinant residues for proton and Ca2+ sensitivity in other DEG/ENaC channels, and a mutation of one conserved residue (S353A) associated with Ca2+ block in rodent BASIC channels instead affected proton sensitivity, all indicative of independent evolution of H+ and Ca2+ sensitivity. Strikingly, TadNaC6 was potently activated by the general DEG/ENaC channel blocker amiloride, a rare feature only reported for the acid-activated channel ASIC3. The sequence and structural divergence of TadNaC6, coupled with its noncanonical functional features, provide unique opportunities for probing the proton, Ca2+, and amiloride regulation of DEG/ENaC channels and insight into the possible core-gating features of ancestral ion channels.