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PDBsum entry 1nft
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Transport protein
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PDB id
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1nft
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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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Alternative structural state of transferrin. The crystallographic analysis of iron-Loaded but domain-Opened ovotransferrin n-Lobe.
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Authors
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K.Mizutani,
H.Yamashita,
H.Kurokawa,
B.Mikami,
M.Hirose.
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Ref.
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J Biol Chem, 1999,
274,
10190-10194.
[DOI no: ]
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PubMed id
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Abstract
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Transferrins bind Fe3+ very tightly in a closed interdomain cleft by the
coordination of four protein ligands (Asp60, Tyr92, Tyr191, and His250 in
ovotransferrin N-lobe) and of a synergistic anion, physiologically bidentate
CO32-. Upon Fe3+ uptake, transferrins undergo a large scale conformational
transition: the apo structure with an opening of the interdomain cleft is
transformed into the closed holo structure, implying initial Fe3+ binding in the
open form. To solve the Fe3+-loaded, domain-opened structure, an ovotransferrin
N-lobe crystal that had been grown as the apo form was soaked with
Fe3+-nitrilotriacetate, and its structure was solved at 2.1 A resolution. The
Fe3+-soaked form showed almost exactly the same overall open structure as the
iron-free apo form. The electron density map unequivocally proved the presence
of an iron atom with the coordination by the two protein ligands of Tyr92-OH and
Tyr191-OH. Other Fe3+ coordination sites are occupied by a nitrilotriacetate
anion, which is stabilized through the hydrogen bonds with the peptide NH groups
of Ser122, Ala123, and Gly124 and a side chain group of Thr117. There is,
however, no clear interaction between the nitrilotriacetate anion and the
synergistic anion binding site, Arg121.
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Figure 2.
Fig. 2. Stereo C[  ]plots
of apo (black) and Fe^3+-soaked (cyan) and holo forms (red) of
ovotransferrin N-lobe. The figures are produced with MOLSCRIPT
(30) and Raster3D (31) as the superimposed ones on domain N2.
The holo (Fe^3+- and CO[3]^2  -loaded
ovotransferrin N-lobe) structure is drawn using the previous
data (8). The apo structure of ovotransferrin N-lobe is the one
employed as the model for the current structural determination
of the Fe^3+-soaked form (see "Experimental Procedures"). The
residue numbers are labeled for the Fe^3+-soaked form. The iron
atom (green sphere) and the side chains (blue) of His^250,
Asp^60, Tyr^92, and Tyr^191 (from top to bottom in this order)
for the Fe^3+-soaked form are also displayed.
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Figure 3.
Fig. 3. Stereo views depicting the iron binding site in
the Fe^3+-soaked form. a, electron density maps (green: 2Fo
 Fc,
contoured at 1  ; blue: Fo
Fc,
contoured at 3 ) obtained
using the reflection data of the Fe^3+-soaked form after
refinement of the model in which the NTA molecule was omitted.
b, anomalous difference Fourier density map contoured at 3 (purple)
calculated with exclusion of an iron atom using the reflection
data of the Fe^3+-soaked form at 7.0-2.1 Å. The final
model is superimposed in stick presentation with atoms in
standard colors.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(1999,
274,
10190-10194)
copyright 1999.
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