Large transient capacitive currents in wild-type lysosomal Cl-/H+ antiporter ClC-7 and residual transport activity in the proton glutamate mutant E312A.
Large transient capacitive currents in wild-type lysosomal Cl-/H+ antiporter ClC-7 and residual transport activity in the proton glutamate mutant E312A.
复制标题
DOI：
10.1085/jgp.202012583
复制
发表时间：
2021-01-04
期刊：
影响因子：
--
通讯作者：
Zifarelli G
中科院分区：
文献类型：
--
作者：
Pusch M;Zifarelli G
Pusch和Zifarelli指出，溶酶体2Cl−/1H+逆向转运体ClC-7介导大的瞬时电容电流，该电流依赖于外部pH和内部Cl−。与其他哺乳动物的ClC逆向转运蛋白不同，ClC-7中保守的质子谷氨酸残基的突变并不会消除转运电流。ClC-7是ClC蛋白家族中的一种溶酶体2氯−/1 H+逆向转运蛋白，由氯离子−通道和其他氯离子−/H+逆向转运蛋白组成。ClC-7及其相关的β亚单位Ostm1的突变会导致人类和小鼠的骨石化和溶酶体储存疾病。以前对其他哺乳动物CLC转运蛋白的研究表明，细胞内保守的谷氨酸残基，即所谓的质子谷氨酸的突变，取消了稳态转运蛋白的活性，但增加了与运输周期部分反应相关的瞬时电容电流。相反，我们观察到野生型ClC-7的大的瞬时电容电流，这取决于外部pH和内部而不是外部的Cl−。谷氨酸质子的突变体E312A也观察到非常相似的瞬时电流。有趣的是，与迄今研究的其他哺乳动物CLC转运蛋白不同，E312A突变强烈地减少但不会取消稳定的转运电流，这可能解释了在E312A鼠系中观察到的中间表型。
Pusch and Zifarelli show that the lysosomal 2 Cl−/1 H+ antiporter ClC-7 mediates large, transient capacitive currents, which depend on external pH and internal Cl−. Unlike in other mammalian CLC antiporters, mutation of a conserved proton glutamate residue in ClC-7 does not abolish transport currents. ClC-7 is a lysosomal 2 Cl−/1 H+ antiporter of the CLC protein family, which comprises Cl− channels and other Cl−/H+ antiporters. Mutations in ClC-7 and its associated β subunit Ostm1 lead to osteopetrosis and lysosomal storage disease in humans and mice. Previous studies on other mammalian CLC transporters showed that mutations of a conserved, intracellularly located glutamate residue, the so-called proton glutamate, abolish steady-state transport activity but increase transient capacitive currents associated with partial reactions of the transport cycle. In contrast, we observed large, transient capacitive currents for the wild-type ClC-7, which depend on external pH and internal, but not external, Cl−. Very similar transient currents were observed for the E312A mutant of the proton glutamate. Interestingly, and unlike in other mammalian CLC transporters investigated so far, the E312A mutation strongly reduces, but does not abolish, stationary transport currents, potentially explaining the intermediate phenotype observed in the E312A mouse line.