4FG6: Structure of EcCLC E148A mutant in Glutamate

CLC proteins underlie muscle, kidney, bone, and other organ system function by catalyzing the transport of Cl(-) ions across cell and organellar membranes. Some CLC proteins are ion channels while others are pumps that exchange Cl(-) for H(+). The pathway through which Cl(-) ions cross the membrane has been characterized, but the transport of H(+) and the principle by which their movement is coupled to Cl(-) movement is not well understood. Here we show that H(+) transport depends not only on the presence of a specific glutamate residue but also the presence of Cl(-) ions. H(+) transport, however, can be isolated and analyzed in the absence of Cl(-) by mutating the glutamate to alanine and adding carboxylate-containing molecules to solution, consistent with the notion that H(+) transfer is mediated through the entry of a carboxylate group into the anion pathway. Cl(-) ions and carboxylate interact with each other strongly. These data support a mechanism in which the glutamate carboxylate functions as a surrogate Cl(-) ion, but it can accept a H(+) and transfer it between the external solution and the central Cl(-) binding site, coupled to the movement of 2 Cl(-) ions.
PDB ID: 4FG6Download
MMDB ID: 101077
PDB Deposition Date: 2012/6/4
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 3.019  Å
Source Organism:
Escherichia coli K-12
Similar Structures:
Biological Unit for 4FG6: trimeric; determined by author
Molecular Components in 4FG6
Label Count Molecule
Proteins (3 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