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PDBsum entry 2h2p
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Ion transport
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PDB id
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2h2p
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Contents |
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444 a.a.
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221 a.a.
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211 a.a.
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References listed in PDB file
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Key reference
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Title
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Uncoupling of a clc cl-/H+ exchange transporter by polyatomic anions.
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Authors
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W.Nguitragool,
C.Miller.
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Ref.
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J Mol Biol, 2006,
362,
682-690.
[DOI no: ]
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PubMed id
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Abstract
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CLC-ec1 is a bacterial archetype of CLC transporters, a ubiquitous class of
proteins that catalyze transmembrane exchange of Cl- and H+ necessary for pH
regulation of numerous physiological processes. Despite a profusion of
high-resolution structures, the molecular mechanism of exchange remains unknown.
Here, we rigorously demonstrate strict exchange stoichiometry of 2 Cl-/1 H+. In
addition to Cl- and Br-, two non-halide ions, NO3- and SCN-, are shown to be
transported by CLC-ec1, but with reduced H+ counter-transport. The loss of
proton coupling to these anions is accompanied by an absence of bound anions in
the central and external Cl- binding sites in the protein's anion selectivity
region, as revealed by crystallographic comparison of Br- and SeCN- bound to
this region.
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Figure 4.
Figure 4. Structure of CLC-ec1. This ribbon representation
of the homodimeric protein, viewed from the membrane plane
(extracellular side above, cytoplasmic side below), emphasizes
the anion-binding region. The inner and central chloride ions
are shown as green spheres, and the external glutamate (E148) is
indicated as a red sphere positioned at one of the carboxylate
oxygen atoms. An expanded representation of this region is shown
below, as viewed from the dimer interface, with the three
anion-binding sites indicated.
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Figure 5.
Figure 5. Anion-binding region of CLC-ec1 in Br^− and
SeCN^−. Crystals of (a) and (b) wild-type CLC-ec1 and (c) and
(d) E148A mutant were grown in (a) and (c) Br^− or (b)and (d)
SeCN^−, and structures were determined to 3.1–3.4 Å.
Shown here is the anion-binding region, with anion-coordinating
side-chains Glu(Ala)148, Ser107, and Tyr445 indicated. Anomalous
difference maps for Br^− (green) or SeCN^− (red) were
calculated and contoured at 4 σ. For E148A in Br^−-the three
anion-binding sites (external, central, and inner) are shown by
anomalous density; in this dataset, inner-site binding is weak.
Not shown here are additional loci of anomalous Se density at
the aqueous surfaces of the transporter; these are probably of
no functional significance, since Br^− is never seen here. PDB
accession number for wild-type in SeCN^− 2H2P; for E148A in
SeCN^− 2H2S.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2006,
362,
682-690)
copyright 2006.
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