Scheel Olaf, Zdebik Anselm A, Lourdel Stéphane, Jentsch Thomas J
Zentrum für Molekulare Neurobiologie, ZMNH, Universität Hamburg, Falkenried 94, D-20246 Hamburg, Germany.
Nature. 2005 Jul 21;436(7049):424-7. doi: 10.1038/nature03860.
Eukaryotic members of the CLC gene family function as plasma membrane chloride channels, or may provide neutralizing anion currents for V-type H(+)-ATPases that acidify compartments of the endosomal/lysosomal pathway. Loss-of-function mutations in the endosomal protein ClC-5 impair renal endocytosis and lead to kidney stones, whereas loss of function of the endosomal/lysosomal protein ClC-7 entails osteopetrosis and lysosomal storage disease. Vesicular CLCs have been thought to be Cl- channels, in particular because ClC-4 and ClC-5 mediate plasma membrane Cl- currents upon heterologous expression. Here we show that these two mainly endosomal CLC proteins instead function as electrogenic Cl-/H+ exchangers (also called antiporters), resembling the transport activity of the bacterial protein ClC-e1, the crystal structure of which has already been determined. Neutralization of a critical glutamate residue not only abolished the steep voltage-dependence of transport, but also eliminated the coupling of anion flux to proton counter-transport. ClC-4 and ClC-5 may still compensate the charge accumulation by endosomal proton pumps, but are expected to couple directly vesicular pH gradients to Cl- gradients.
CLC基因家族的真核成员作为质膜氯离子通道发挥作用，或者可能为使内体/溶酶体途径各区室酸化的V型H(+) -ATP酶提供中和性阴离子电流。内体蛋白ClC -5的功能丧失突变会损害肾脏内吞作用并导致肾结石，而内体/溶酶体蛋白ClC -7的功能丧失会引发骨质石化和溶酶体贮积病。囊泡型CLC一直被认为是氯离子通道，特别是因为ClC -4和ClC -5在异源表达时介导质膜氯离子电流。在此我们表明，这两种主要存在于内体的CLC蛋白实际上作为电生性Cl-/H+交换体（也称为反向转运体）发挥作用，类似于细菌蛋白ClC -e1的转运活性，其晶体结构已被确定。一个关键谷氨酸残基的中和不仅消除了转运对电压的强烈依赖性，还消除了阴离子通量与质子反向转运的偶联。ClC -4和ClC -5可能仍能补偿内体质子泵引起的电荷积累，但预计会直接将囊泡pH梯度与Cl-梯度偶联起来。
