Sandboxjg
From Proteopedia
ClC Transporter
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The is a transmembrane voltage-gated CLC transporter found in Eschrecheria Coli. It is essential for the maintenance of proper membrane potential in muscle cells and some neurons, for the transportion of electrolytes across epithelial layers, and in maintaining proper cell volume.
Roderick MacKinnon and his team determined the structure of the protein and concluded that it was an ion channel. Accardi and Miller established that the protein also functioned as a transporter, by means of a 2:1 chloride ion-hydrogen ion exchange mechanism.
The CLC-ec1 transporter is a protein dimer made up of two independently functioning anti-parallel polypeptide chains. The chains extend from the inside to the outside of the plasma membrane creating a passage. Its structure allows it to use electrostatic interactions with alpha-helical dipoles and chemical groups coordinated with nitrogen atoms and carboxyl groups in order to filter Cl- and H+ ions. Because each polypeptide chain functions independently, we will focus on the structure of one pore.
Each pore has two essential glutamate residues: one functions as a gate to mediate the transport of chloride ions into and out of the protein, and the other (Glu 203) is thought to be involved in hydrogen ion selectivity. There are 3 chloride binding sites in each channel, an exterior binding site, a central binding site, and an interior binding site. When the protein is inactive Glu 148 occupies the exterior binding site. When the protein is active Glu 148 leaves the site and allows ion exchange to occur.
One of the interesting properties of this protein is that it can function as either a channel or a transporter. For instance, with certain mutations concerning the Glu 148,hydrogen ion activity is impaired, but chloride ions can still move freely through the protein. Other mutations can have the potential to cause diseases like cystic fibrosis, myotonia congenita, epilepsy, and others. To see the test
