2htk | pdb_00002htk
Structure of the Escherichia coli ClC chloride channel Y445A mutant and Fab complex
Structural highlights
Function[CLCA_ECOLI] Proton-coupled chloride transporter. Functions as antiport system and exchanges two chloride ions for 1 proton. Probably acts as an electrical shunt for an outwardly-directed proton pump that is linked to amino acid decarboxylation, as part of the extreme acid resistance (XAR) response.[1] [2] [3] [4] [5] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe 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. 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[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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