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PDBsum entry 2d3i
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Metal transport
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PDB id
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2d3i
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References listed in PDB file
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Key reference
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Title
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Structure of aluminium-Bound ovotransferrin at 2.15 angstroms resolution.
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Authors
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K.Mizutani,
B.Mikami,
S.Aibara,
M.Hirose.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2005,
61,
1636-1642.
[DOI no: ]
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PubMed id
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Abstract
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Transferrin, well known as an iron-transport protein, can bind other metal ions,
including toxic ones, and is considered to play an important role in the
transportation of such metal ions. Here, a crystal structure of aluminium-bound
transferrin is described for the first time. Colourless needle-shaped crystals
of aluminium-bound ovotransferrin were obtained in PEG 400 solution. Structural
determination was performed by molecular replacement using diferric (iron-bound)
ovotransferrin as a model and the structural refinement was performed in the
50-2.15 Angstroms resolution range. The overall organization of the
aluminium-bound form is almost the same as the iron-bound form: the protein is
folded into two homologous lobes (N- and C-lobes) with two domains; two
metal-binding sites are located within the inter-domain clefts of each lobe.
Four residues (one Asp, two Tyr and one His) and one bicarbonate anion were
found to bind an aluminium ion in either lobe, as in the iron-bound form. The
highly similar domain-closed structure of the Al(3+)-bound form may permit the
binding of Al(3+)-bound transferrin to the transferrin receptor. An unusual
interaction, the dilysine trigger, which facilitates iron release at low pH in
the endosome, was also found in the Al(3+)-bound form. These findings support
the participation of transferrin in the transport of Al(3+) ions in vivo.
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Figure 3.
Figure 3
Stereo diagrams depicting the aluminium-binding sites. Electron-density maps (2F[o] -
F[c], contoured at 1 [sigma] ; green) are shown for the Al3+-binding sites in (a) the
N-lobe and (b) the C-lobe. Electron-density omit maps (F[o] - F[c], contoured at 3
[sigma] ; purple and orange) were calculated after refinement using a model in which
Al3+ ions or bicarbonate anions were omitted. The final model is superimposed in a stick
presentation with atoms in standard colours for the Al3+-coordinating residues (Asp60,
Tyr92, Tyr191 and His250 for the N-lobe; Asp395, Tyr431, Tyr524 and His592 for the C-lobe)
and bicarbonate anions. Al3+ atoms are shown by small spheres coloured cyan. The figures
were prepared with the programs BobScript (Esnouf, 1999 [Esnouf, R. M. (1999). Acta
Cryst. D55, 938-940.]-[bluearr.gif] ) and Raster3D (Merritt & Bacon, 1997
[Merritt, E. A. & Bacon, D. J. (1997). Methods Enzymol. 277, 505-524.]-[bluearr.gif]
).
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The above figure is
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(2005,
61,
1636-1642)
copyright 2005.
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