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'''Structure of the Escherichia coli ClC chloride channel Y445L mutant and Fab complex''' | '''Structure of the Escherichia coli ClC chloride channel Y445L mutant and Fab complex''' | ||
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[[Category: Miller, C.]] | [[Category: Miller, C.]] | ||
[[Category: Williams, C.]] | [[Category: Williams, C.]] | ||
[[Category: | [[Category: Clc family of channel and transporter]] | ||
[[Category: | [[Category: Fab complex]] | ||
[[Category: | [[Category: H+/cl- antiporter,membrane protein]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 06:40:29 2008'' | |||
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Revision as of 06:40, 4 May 2008
Structure of the Escherichia coli ClC chloride channel Y445L mutant and Fab complex
OverviewOverview
The Cl-/H+ exchange-transporter CLC-ec1 mediates stoichiometric transmembrane exchange of two Cl- ions for one proton. A conserved tyrosine residue, Y445, coordinates one of the bound Cl- ions visible in the structure of this protein and is located near the intersection of the Cl- and H+ pathways. Mutants of this tyrosine were scrutinized for effects on the coupled transport of Cl- and H+ determined electrophysiologically and on protein structure determined crystallographically. Despite the strong conservation of Y445 in the CLC family, substitution of F or W at this position preserves wild-type transport behavior. Substitution by A, E, or H, however, produces uncoupled proteins with robust Cl- transport but greatly impaired movement of H+. The obligatory 2 Cl-/1 H+ stoichiometry is thus lost in these mutants. The structures of all the mutants are essentially identical to wild-type, but apparent anion occupancy in the Cl- binding region correlates with functional H+ coupling. In particular, as determined by anomalous diffraction in crystals grown in Br-, an electrophysiologically competent Cl- analogue, the well-coupled transporters show strong Br- electron density at the "inner" and "central" Cl- binding sites. However, in the uncoupled mutants, Br- density is absent at the central site, while still present at the inner site. An additional mutant, Y445L, is intermediate in both functional and structural features. This mutant clearly exchanges H+ for Cl-, but at a reduced H+-to-Cl- ratio; likewise, both the central and inner sites are occupied by Br-, but the central site shows lower Br- density than in wild-type (or in Y445F,W). The correlation between proton coupling and central-site occupancy argues that halide binding to the central transport site somehow facilitates movement of H+, a synergism that is not readily understood in terms of alternating-site antiport schemes.
About this StructureAbout this Structure
2HT3 is a Single protein structure of sequence from Escherichia coli and Mus musculus. Full crystallographic information is available from OCA.
ReferenceReference
Synergism between halide binding and proton transport in a CLC-type exchanger., Accardi A, Lobet S, Williams C, Miller C, Dutzler R, J Mol Biol. 2006 Sep 29;362(4):691-9. Epub 2006 Aug 2. PMID:16949616 Page seeded by OCA on Sun May 4 06:40:29 2008