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PDBsum entry 2osv
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Metal transport
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PDB id
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2osv
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References listed in PDB file
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Key reference
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Title
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Crystal structure of the zinc-Binding transport protein znua from escherichia coli reveals an unexpected variation in metal coordination.
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Authors
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H.Li,
G.Jogl.
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Ref.
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J Mol Biol, 2007,
368,
1358-1366.
[DOI no: ]
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PubMed id
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Abstract
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Bacterial ATP-binding cassette transport systems for high-affinity uptake of
zinc and manganese use a cluster 9 solute-binding protein. Structures of four
cluster 9 transport proteins have been determined previously. However, the
structural determinants for discrimination between zinc and manganese remain
under discussion. To further investigate the variability of metal binding sites
in bacterial transporters, we have determined the structure of the zinc-bound
transport protein ZnuA from Escherichia coli to 1.75 A resolution. The overall
structure of ZnuA is similar to other solute-binding transporters. A scaffolding
alpha-helix forms the backbone for two structurally related globular domains.
The metal-binding site is located at the domain interface. The bound zinc ion is
coordinated by three histidine residues (His78, His161 and His225) and one
glutamate residue (Glu77). The functional role of Glu77 for metal binding is
unexpected, because this residue is not conserved in previously determined
structures of zinc and manganese-specific transport proteins. The observed metal
coordination by four protein residues differs significantly from the
zinc-binding site in the ZnuA transporter from Synechocystis 6803, which binds
zinc via three histidine residues. In addition, the E. coli ZnuA structure
reveals the presence of a disulfide bond in the C-terminal globular domain that
is not present in previously determined cluster 9 transport protein structures.
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Figure 1.
Figure 1. Structure of ZnuA. (a) Schematic representation of
the structure of ZnuA. Metal-coordinating residues are shown as
sticks, the zinc ion is shown as purple sphere. The position of
the disordered loop between residues 135 and 157 is indicated by
a black line. (b) Final 2F[o–]F[c] electron density map
(contoured at 1σ) for residues in the active site region is
shown in orange and grey. The anomalous difference Fourier map
for data collected at the zinc peak wavelength is shown at a 5σ
contour level in dark blue.
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Figure 2.
Figure 2. The ZnuA metal-binding site. (a) Stereo
representation of the ZnuA metal-binding site. Residues in the
first and second coordination shell and the disulfide
bond-forming cysteine residues are shown in orange sticks. The
zinc ion is shown as purple sphere. Hydrophobic residues
surrounding the metal-binding site are shown in grey sticks. (b)
Close-up view of the metal-binding site. The interatomic
distances between coordinating residues and solvent water
molecules are indicated.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2007,
368,
1358-1366)
copyright 2007.
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