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Ion permeation through a Cl--selective channel designed from a CLC Cl-/H+ exchanger.

TitleIon permeation through a Cl--selective channel designed from a CLC Cl-/H+ exchanger.
Publication TypeJournal Article
Year of Publication2008
AuthorsJayaram H, Accardi A, Wu F, Williams C, Miller C
JournalProc Natl Acad Sci U S A
Date Published2008 Aug 12
KeywordsAmino Acid Substitution, Animals, Chloride Channels, Chlorides, Crystallography, X-Ray, Humans, Ion Transport, Point Mutation, Protein Structure, Tertiary, Protons

The CLC family of Cl(-)-transporting proteins includes both Cl(-) channels and Cl(-)/H(+) exchange transporters. CLC-ec1, a structurally known bacterial homolog of the transporter subclass, exchanges two Cl(-) ions per proton with strict, obligatory stoichiometry. Point mutations at two residues, Glu(148) and Tyr(445), are known to impair H(+) movement while preserving Cl(-) transport. In the x-ray crystal structure of CLC-ec1, these residues form putative "gates" flanking an ion-binding region. In mutants with both of the gate-forming side chains reduced in size, H(+) transport is abolished, and unitary Cl(-) transport rates are greatly increased, well above values expected for transporter mechanisms. Cl(-) transport rates increase as side-chain volume at these positions is decreased. The crystal structure of a doubly ungated mutant shows a narrow conduit traversing the entire protein transmembrane width. These characteristics suggest that Cl(-) flux through uncoupled, ungated CLC-ec1 occurs via a channel-like electrodiffusion mechanism rather than an alternating-exposure conformational cycle that has been rendered proton-independent by the gate mutations.

Alternate JournalProc. Natl. Acad. Sci. U.S.A.
PubMed ID18678918
PubMed Central IDPMC2516207
Grant ListP30 EB009998 / EB / NIBIB NIH HHS / United States