Slowly voltage-gated channel mediating the exchange of chloride ions against protons. Functions as antiporter and contributes to the acidification of the lysosome lumen.
Mutations in the ClC-7/Ostm1 ion transporter lead to osteopetrosis and lysosomal storage disease. Its lysosomal localization hitherto precluded detailed functional characterization. Using a mutated ClC-7 that reaches the plasma membrane, we now show that both the aminoterminus and transmembrane span of the Ostm1 β-subunit are required for ClC-7 Cl(-)/H(+)-exchange, whereas the Ostm1 transmembrane domain suffices for its ClC-7-dependent trafficking to lysosomes. ClC-7/Ostm1 currents were strongly outwardly rectifying owing to slow gating of ion exchange, which itself displays an intrinsically almost linear voltage dependence. Reversal potentials of tail currents revealed a 2Cl(-)/1H(+)-exchange stoichiometry. Several disease-causing CLCN7 mutations accelerated gating. Such mutations cluster to the second cytosolic cystathionine-β-synthase domain and potential contact sites at the transmembrane segment. Our work suggests that gating underlies the rectification of all endosomal/lysosomal CLCs and extends the concept of voltage gating beyond channels to ion exchangers.
Lysosomes are the stomachs of the cell-terminal organelles on the endocytic pathway where internalized macromolecules are degraded. Containing a wide range of hydrolytic enzymes, lysosomes depend on maintaining acidic luminal pH values for efficient function. Although acidification is mediated by a V-type proton ATPase, a parallel anion pathway is essential to allow bulk proton transport. The molecular identity of this anion transporter remains unknown. Recent results of knockout experiments raise the possibility that ClC-7, a member of the CLC family of anion channels and transporters, is a contributor to this pathway in an osteoclast lysosome-like compartment, with loss of ClC-7 function causing osteopetrosis. Several mammalian members of the CLC family have been characterized in detail; some (including ClC-0, ClC-1 and ClC-2) function as Cl--conducting ion channels, whereas others act as Cl-/H+antiporters (ClC-4 and ClC-5). However, previous attempts at heterologous expression of ClC-7 have failed to yield evidence of functional protein, so it is unclear whether ClC-7 has an important function in lysosomal biology, and also whether this protein functions as a Cl- channel, a Cl-/H+ antiporter, or as something else entirely. Here we directly demonstrate an anion transport pathway in lysosomes that has the defining characteristics of a CLC Cl-/H+ antiporter and show that this transporter is the predominant route for Cl- through the lysosomal membrane. Furthermore, knockdown of ClC-7 expression by short interfering RNA can essentially ablate this lysosomal Cl-/H+ antiport activity and can strongly diminish the ability of lysosomes to acidify in vivo, demonstrating that ClC-7 is a Cl-/H+ antiporter, that it constitutes the major Cl- permeability of lysosomes, and that it is important in lysosomal acidification.
Enables the active transport of a solute across a membrane by a mechanism whereby two or more species are transported in opposite directions in a tightly coupled process not directly linked to a form of energy other than chemiosmotic energy. The reaction is: solute A(out) + solute B(in) = solute A(in) + solute B(out).
Catalysis of facilitated diffusion of a chloride (by an energy-independent process) involving passage through a transmembrane aqueous pore or channel without evidence for a carrier-mediated mechanism.
We cloned two novel members of the CLC chloride channel family from rat and human brain. ClC-6 is a 97-kDa protein, and ClC-7 a 89-kDa protein roughly 45% identical with ClC-6. Together they define a new branch of this gene family. Both genes are very broadly expressed, e.g. in brain, testes, muscle and kidney. In mouse embryos, both genes are expressed as early as day 7. While the human gene for ClC-6 is located on human chromosome 1p36 and shares this region with hClC-Ka and hClC-Kb, ClC-7 is on 16p13. ClC-6 has a highly conserved glycosylation site between transmembrane domains D8 and D9, while ClC-7 is the only known eukaryotic ClC protein which lacks this site. Hydropathy analysis indicates that domain D4 cannot serve as a transmembrane domain. Both ClC-6 and ClC-7 cannot be expressed as chloride channels in Xenopus oocytes, either singly or in combination.
Catalysis of the transmembrane transfer of a chloride ion by a voltage-gated channel. A voltage-gated channel is a channel whose open state is dependent on the voltage across the membrane in which it is embedded.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a pH stimulus.
The directed movement of substances (such as macromolecules, small molecules, ions) into, out of or within a cell, or between cells, or within a multicellular organism by means of some agent such as a transporter or pore.
We cloned two novel members of the CLC chloride channel family from rat and human brain. ClC-6 is a 97-kDa protein, and ClC-7 a 89-kDa protein roughly 45% identical with ClC-6. Together they define a new branch of this gene family. Both genes are very broadly expressed, e.g. in brain, testes, muscle and kidney. In mouse embryos, both genes are expressed as early as day 7. While the human gene for ClC-6 is located on human chromosome 1p36 and shares this region with hClC-Ka and hClC-Kb, ClC-7 is on 16p13. ClC-6 has a highly conserved glycosylation site between transmembrane domains D8 and D9, while ClC-7 is the only known eukaryotic ClC protein which lacks this site. Hydropathy analysis indicates that domain D4 cannot serve as a transmembrane domain. Both ClC-6 and ClC-7 cannot be expressed as chloride channels in Xenopus oocytes, either singly or in combination.
The CLC channel family contains both chloride channels and proton-coupled anion transporters that exchange chloride or another anion for protons. The presence of conserved gating glutamate residues is typical for family members that function as antiporters (By similarity).
Protein involved in the transport of a solute across a biological membrane coupled, directly, to the transport of a different solute in the opposite direction.
Protein involved in the transport of ions. Such proteins are usually transmembrane and mediate a movement of ions across cell membranes. Transport may be passive (facilitated diffusion; down the electrochemical gradient), or active (against the electrochemical gradient). Active transport requires energy which may come from light, oxidation reactions, ATP hydrolysis, or cotransport of other ions or molecules.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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