2FEE: Structure Of The Cl-H+ EXCHANGER CLC-Ec1 From E.Coli In Nabr

CLC-ec1 is a prokaryotic CLC-type Cl(-)/H+ exchange transporter. Little is known about the mechanism of H+ coupling to Cl-. A critical glutamate residue, E148, was previously shown to be required for Cl(-)/H+ exchange by mediating proton transfer between the protein and the extracellular solution. To test whether an analogous H+ acceptor exists near the intracellular side of the protein, we performed a mutagenesis scan of inward-facing carboxyl-bearing residues and identified E203 as the unique residue whose neutralization abolishes H+ coupling to Cl- transport. Glutamate at this position is strictly conserved in all known CLCs of the transporter subclass, while valine is always found here in CLC channels. The x-ray crystal structure of the E203Q mutant is similar to that of the wild-type protein. Cl- transport rate in E203Q is inhibited at neutral pH, and the double mutant, E148A/E203Q, shows maximal Cl- transport, independent of pH, as does the single mutant E148A. The results argue that substrate exchange by CLC-ec1 involves two separate but partially overlapping permeation pathways, one for Cl- and one for H+. These pathways are congruent from the protein's extracellular surface to E148, and they diverge beyond this point toward the intracellular side. This picture demands a transport mechanism fundamentally different from familiar alternating-access schemes.
PDB ID: 2FEEDownload
MMDB ID: 36898
PDB Deposition Date: 2005/12/15
Updated in MMDB: 2011/10
Experimental Method:
x-ray diffraction
Resolution: 3.2  Å
Source Organism:
Homo sapiens
Similar Structures:
Biological Unit for 2FEE: hexameric; determined by author
Molecular Components in 2FEE
Label Count Molecule
Proteins (6 molecules)
H(+)/cl(-) Exchange Transporter Clca(Gene symbol: clcA)
Molecule annotation
FAB Fragment, Heavy Chain
Molecule annotation
FAB Fragment, Light Chain
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB