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PDBsum entry 1u7c
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Transport protein
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PDB id
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1u7c
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Mechanism of ammonia transport by amt/mep/rh: structure of amtb at 1.35 a.
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Authors
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S.Khademi,
J.O'Connell,
J.Remis,
Y.Robles-Colmenares,
L.J.Miercke,
R.M.Stroud.
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Ref.
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Science, 2004,
305,
1587-1594.
[DOI no: ]
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PubMed id
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Abstract
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The first structure of an ammonia channel from the Amt/MEP/Rh protein
superfamily, determined to 1.35 angstrom resolution, shows it to be a channel
that spans the membrane 11 times. Two structurally similar halves span the
membrane with opposite polarity. Structures with and without ammonia or methyl
ammonia show a vestibule that recruits NH4+/NH3, a binding site for NH4+, and a
20 angstrom-long hydrophobic channel that lowers the NH4+ pKa to below 6 and
conducts NH3. Favorable interactions for NH3 are seen within the channel and use
conserved histidines. Reconstitution of AmtB into vesicles shows that AmtB
conducts uncharged NH3.
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Figure 4.
Fig. 4. (A) Electron density (2Fo-Fc) contoured at 1.5  (blue) for the
two-histidine region and surrounding structure, including
conserved Asp160 that accepts four short hydrogen bonds (dashed
yellow). Additional peaks Am2, Am3, and Am4 seen when
crystallized with 25 mM ammonium sulfate are defined in the
Fo-Fc omit map at 1.5 (in red),
indicating putative NH[3] molecule positions (blue spheres). The
hydrogen-bonding network shows interactions between His168 and
His318 and NH[3] peaks in yellow (distances in red). (B) Stereo
view of the two-histidine center of the channel. Surrounding
hydrophobic residues are shown in ball and stick representation.
The surface representation covers other surrounding amino acids.
Three ammonia-dependent sites are shown (blue spheres) with
associated distances (dashed yellow line and yellow labels).
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Figure 6.
Fig. 6. The deduced mechanism of conductance is summarized. The
low electron density for NH[3] may represent substitutional
interchange or relative freedom of NH[3] within the hydrophobic
channel. NH[3] normally undergoes rapid inversion. This may be
impeded against the weak hydrogen bond C-H donors of imidazole.
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The above figures are
reprinted
by permission from the AAAs:
Science
(2004,
305,
1587-1594)
copyright 2004.
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