Chloride channel

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Chloride channel
Chloride channel
Ribbon model of the ClC of E. coli from the side and above, according to PDB  3NMO
Identifier
Gene name (s) CLCN1 , CLCN2 , CLCN3 , CLCN4 , CLCN5 , CLCN6 , CLCN7
Transporter classification
TCDB 2.A.49
designation Chloride channels
Occurrence
Parent taxon Creature
Exceptions several protozoa with a small genome

As chloride channels in the are physiology and cell biology ion channels refers to a specific and more or less selective conductivity for chloride - ions have. The subfamily of the epithelial calcium-regulated chloride channels (E-ClC) are seen as an independent group, since their channel function is now questionable and they also do not have the CBS domain of the ClC family.

The protein family of the chloride channels ( ClC , derived from the English chloride channel ) includes chloride channels, but also secondary active chloride / proton exchangers ( transporters ). Structural homologs of this family can be found across all biological realms, from the simple intestinal bacterium Escherichia coli to plants and mammals. The channels take on different biological functions, such as B. the participation in the regulation of the cellular water balance or the stabilization of the resting membrane potential in the skeletal muscle.

Scientific history

In 1980, Miller discovered, among other things, the first chloride channel in vesicles of the electrical organ of the torpedo tube . On the basis of single-channel studies, he predicted a double-pore channel, which has since been confirmed by a large number of studies. In the 1990s, Thomas Jentsch studied the protein family at the molecular level. In 2002, R. Dutzler solved the structures of the ClC transporters EcClC and StClC from E. coli and Salmonella typhi by X-ray crystallography (2.5–3.5  Å ) and thus set the basis for a molecular understanding of their function.

Isoforms in humans

Nine isoforms of the ClC family are found in humans . Some of these are in the plasma membranes expressing , others in the membranes of intracellular organelles . ClC-1, for example, is found in the plasma membrane of skeletal muscle cells and is involved in stabilizing the resting membrane potential .

The individual human chloride transporters: ClC-1, ClC-2, ClC-3, ClC-4, ClC-5 , ClC-6, ClC-7, ClC-8, ClC-9.

Chloride channels in plants

Chloride channels perform different functions in plants, depending on their location and ion affinity. The seven chloride channels from Arabidopsis thaliana , AtCLCa to AtCLCg have been studied best. The channels are located in the membranes of various organelles and there fulfill the function of anion transporters. AtCLCa and AtCLCe transport nitrate instead of chloride across membranes.

The structure

ClC transporters and channels are diamond-shaped homodimers . Each subunit has its own hourglass-shaped pore with the narrowest point in the center of the membrane. From the extra- and intracellular side, two extensive water-filled atria extend into the pore; in the center, the pore is anhydrous. Three ion binding sites are assumed: two each at the contact area between the atrium and the interior of the pores and one in the anhydrous center. During permeation , the ions are coordinated by partially charged side chain hydroxyl groups and some main chain nitrogen atoms, which together form the selectivity filter and energetically balance the ions through the hydrophobic part of the membrane.

See also

Individual evidence

  1. ↑ TCDB: Epithelial chloride channels
  2. ^ C. Miller, MM White: A voltage-dependent chloride conductance channel from Torpedo electroplax membrane. In: Ann NY Acad Sci. 341, 1980, pp. 534-551. PMID 6249158
  3. ^ R. Dutzler, EB Campbell, M. Cadene, BT Chait, R. MacKinnon: X-ray structure of a ClC chloride channel at 3.0 A reveals the molecular basis of anion selectivity. In: Nature . 415 (6869), Jan 17, 2002, pp. 276-277. PMID 11796999
  4. ↑ Cloning and molecular analyzes of the Arabidopsis thaliana chloride channel gene family. In: Plant Science. 2009, doi: 10.1016 / j.plantsci.2009.02.006 .
  5. ↑ Two anion transporters AtClCa and AtClCe fulfill interconnecting but not redundant roles in nitrate assimilation pathways. In: New Phytologist. 2009; doi: 10.1111 / j.1469-8137.2009.02837.x .

literature

Web links