Referenced in: none

Automatically associated channels: ClC4

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

Authors: Hariharan Jayaram, Alessio Accardi, Fang Wu, Carole Williams, Christopher Miller

Journal, date & volume: Proc. Natl. Acad. Sci. U.S.A., 2008 Aug 12 , 105, 11194-9

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/18678918

Abstract
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.