Ion selectivity is a defining feature of a given ion channel and is considered immutable. Here we show that ion selectivity of the lysosomal ion channel TPC2, which is hotly debated (Calcraft et al., 2009; Guo et al., 2017; Jha et al., 2014; Ruas et al., 2015; Wang et al., 2012), depends on the activating ligand. A high-throughput screen identified two structurally distinct TPC2 agonists. One of these evoked robust Ca2+-signals and non-selective cation currents, the other weaker Ca2+-signals and Na+-selective currents. These properties were mirrored by the Ca2+-mobilizing messenger, NAADP and the phosphoinositide, PI(3,5)P2, respectively. Agonist action was differentially inhibited by mutation of a single TPC2 residue and coupled to opposing changes in lysosomal pH and exocytosis. Our findings resolve conflicting reports on the permeability and gating properties of TPC2 and they establish a new paradigm whereby a single ion channel mediates distinct, functionally-relevant ionic signatures on demand.
离子选择性是特定离子通道的决定性特征,被认为是不可改变的。在这里,我们证明了溶酶体离子通道 TPC2 的离子选择性取决于激活配体,这一点引起了激烈的争论(Calcraft 等人,2009 年;Guo 等人,2017 年;Jha 等人,2014 年;Ruas 等人,2015 年;Wang 等人,2012 年)。高通量筛选发现了两种结构不同的 TPC2 激动剂。其中一种能唤起强烈的 Ca2+ 信号和非选择性阳离子电流,另一种则能唤起较弱的 Ca2+ 信号和 Na+ 选择性电流。这些特性分别由 Ca2+ 迁移信使 NAADP 和磷酸肌醇 PI(3,5)P2 反映出来。单个 TPC2 残基的突变会不同程度地抑制激动剂的作用,并与溶酶体 pH 值和外泌作用的对立变化相耦合。我们的发现解决了有关 TPC2 通透性和门控特性的相互矛盾的报道,并建立了一种新的范式,即单一离子通道可根据需要介导不同的、功能相关的离子特征。