Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, GA.
Department of Physiology & Biophysics, Rush University, Chicago, IL.
J Gen Physiol. 2018 Jun 4;150(6):835-850. doi: 10.1085/jgp.201711967. Epub 2018 May 9.
Voltage-gated proton channels, H1, were first reported in snail neurons. These H channels open very rapidly, two to three orders of magnitude faster than mammalian H1. Here we identify an H1 gene in the snail and verify protein level expression by Western blotting of brain lysate. Expressed in mammalian cells, HtH1 currents in most respects resemble those described in other snails, including rapid activation, 476 times faster than hH1 (human) at pH 7, between 50 and 90 mV. In contrast to most H1, activation of HtH1 is exponential, suggesting first-order kinetics. However, the large gating charge of ∼5.5 suggests that HtH1 functions as a dimer, evidently with highly cooperative gating. HtH1 opening is exquisitely sensitive to pH, whereas closing is nearly independent of pH Zn and Cd inhibit HtH1 currents in the micromolar range, slowing activation, shifting the proton conductance-voltage (-) relationship to more positive potentials, and lowering the maximum conductance. This is consistent with HtH1 possessing three of the four amino acids that coordinate Zn in mammalian H1. All known H1 exhibit ΔpH-dependent gating that results in a 40-mV shift of the - relationship for a unit change in either pH or pH This property is crucial for all the functions of H1 in many species and numerous human cells. The HtH1 channel exhibits normal or supernormal pH dependence, but weak pH dependence. Under favorable conditions, this might result in the HtH1 channel conducting inward currents and perhaps mediating a proton action potential. The anomalous ΔpH-dependent gating of HtH1 channels suggests a structural basis for this important property, which is further explored in this issue (Cherny et al. 2018. https://doi.org/10.1085/jgp.201711968).
电压门控质子通道 H1 最初在蜗牛神经元中被报道。这些 H 通道迅速打开，比哺乳动物 H1 快两到三个数量级。在这里，我们在蜗牛中鉴定出一个 H1 基因，并通过脑裂解物的 Western blot 验证蛋白质水平的表达。在哺乳动物细胞中表达时，HtH1 电流在大多数方面与在其他蜗牛中描述的相似，包括快速激活，在 pH 7 时比 hH1（人类）快 476 倍，在 50 至 90 mV 之间。与大多数 H1 不同，HtH1 的激活呈指数级，表明一级动力学。然而，大的门控电荷约为 5.5，表明 HtH1 作为二聚体起作用，显然具有高度协同的门控。HtH1 的打开对 pH 非常敏感，而关闭几乎与 pH 无关。Zn 和 Cd 以微摩尔范围抑制 HtH1 电流，减慢激活，将质子电导-电压 (-) 关系移至更正的电位，并降低最大电导。这与 HtH1 具有在哺乳动物 H1 中协调 Zn 的四个氨基酸中的三个一致。所有已知的 H1 都表现出 ΔpH 依赖性门控，导致在 pH 或 pH 发生单位变化时，-关系发生 40 mV 偏移。这种特性对于 H1 在许多物种和许多人类细胞中的所有功能都是至关重要的。HtH1 通道表现出正常或超正常的 pH 依赖性，但 pH 依赖性较弱。在有利条件下，这可能导致 HtH1 通道传导内向电流，并可能介导质子动作电位。HtH1 通道异常的 ΔpH 依赖性门控表明了这种重要特性的结构基础，本研究进一步探讨了这一特性（Cherny 等人，2018. https://doi.org/10.1085/jgp.201711968）。
