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Introduction
In vertebrates the CLC chloride channel serves several important functions. In skeletal muscles this channel stabilizes the resting membrane potential and regulates electrical excitability. In the kidney this channel helps produce transepithelial fluid and electrolyte transport.
Wire Frame
(the top part of the channel is the extracellular region where the concentration of chloride ions is high. The bottom is the intracelluar region)
Quaternary Structure
(2 subunits)
Backbone
Cartoon showing hydrogen bonds
(a total of 18 alpha helices)
Cartoon and Wireframe
Chloride Channel Subunits
Consisting of two identical pores, the antiparallel architecture
creates two individual selectivity filters that stabilizes the chloride
ion by electrostatic interactions with the alpha-helix dipoles and by
coordination with nitrogen atoms and hydroxyl groups. .
One Subunit
Both Subunits
Both Subunits in carton
Chloride Binding Site
The favorable electrostatic environment for chloride comes not from positive charges of arginine or lysine but from the partial positive charges of helix dipole interactions and by contacts with main-chain nitrogen and oxygen atoms. A full positive charge would cause the chloride ion to bind too tightly.
Backbone -
Cl Ion Binding Site
(located at the N
termini of alpha-helices and a strong peak of electron density)
Ser 107 and Tyr 445
coordinate the chloride ion by side-chain oxygen atoms. Because of its aromatic ring, Tyr is an excellent proton donor.
Ile356 and Phe357
coordinate the chloride ion by main-chain chain
nitrogen atoms
Other Chloride ion Coordinators
Ion Binding Site
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