Download MendeleyIon permeation through a Cl--selective channel designed from a CLC Cl-/H+ exchanger
Jayaram, H., Accardi, A., Wu, F., Williams, C., Miller, C.(2008) Proc Natl Acad Sci U S A 105: 11194-11199
- PubMed: 18678918
- DOI: https://doi.org/10.1073/pnas.0804503105
- Primary Citation of Related Structures:
3DET - PubMed 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.
Organizational Affiliation:
Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454, USA.
