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'''Structure of the E203Q mutant of the Cl-/H+ exchanger CLC-ec1 from E.Coli''' | '''Structure of the E203Q mutant of the Cl-/H+ exchanger CLC-ec1 from E.Coli''' | ||
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[[Category: Walden, M P.]] | [[Category: Walden, M P.]] | ||
[[Category: Williams, C.]] | [[Category: Williams, C.]] | ||
[[Category: | [[Category: Chloride/proton exchange transporter]] | ||
[[Category: | [[Category: Clc-ec1]] | ||
[[Category: | [[Category: Clca_ecoli]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 03:47:54 2008'' | |||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | |||
Revision as of 00:47, 4 May 2008
Structure of the E203Q mutant of the Cl-/H+ exchanger CLC-ec1 from E.Coli
Overview
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.
About this Structure
2FED is a Single protein structure of sequence from Escherichia coli and Homo sapiens. Full crystallographic information is available from OCA.
Reference
Separate ion pathways in a Cl-/H+ exchanger., Accardi A, Walden M, Nguitragool W, Jayaram H, Williams C, Miller C, J Gen Physiol. 2005 Dec;126(6):563-70. PMID:16316975 Page seeded by OCA on Sun May 4 03:47:54 2008
