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PDBsum entry 1gv8
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Iron transport
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PDB id
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1gv8
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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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The mechanism of iron uptake by transferrins: the X-Ray structures of the 18 kda nii domain fragment of duck ovotransferrin and its nitrilotriacetate complex.
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Authors
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P.Kuser,
D.R.Hall,
M.L.Haw,
M.Neu,
R.W.Evans,
P.F.Lindley.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2002,
58,
777-783.
[DOI no: ]
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PubMed id
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Abstract
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In a previous paper [Lindley et al. (1993), Acta Cryst. D49, 292-304], the X-ray
structure analysis of the 18 kDa fragment of duck ovotransferrin, corresponding
to the NII domain of the intact protein, was reported at a resolution of 2.3 A.
In this structure, the Fe(III) cation binds to two tyrosine residues and the
synergistic carbonate anion in an identical manner to that found in the intact
protein. However, the aspartate and histidine residues, normally involved in
iron binding in transferrins, are absent in the fragment and it was not possible
to unequivocally define what had replaced them. The electron density was
tentatively assigned to be a mixture of peptides, presumably resulting from the
proteolytic preparation of the fragment, binding to the iron through their amino
and carboxylate termini. A more recent X-ray analysis of the fragment, from a
different preparation, has resulted in a structure at 1.95 A, in which glycine
appears to be the predominant residue bound to the cation. In an alternative
attempt to clarify the binding of iron to the 18 kDa fragment, the metal was
removed by dialysis and replaced in the form of ferric nitrilotriacetate.
Crystallization of this complex has resulted in an X-ray structure at 1.90 A in
which the Fe(III) is bound to the synergistic carbonate anion and only one
tyrosine residue in a manner almost identical to the intact protein. The
carboxylate groups and the tertiary amino group of the nitrilotriacetate occupy
the remaining coordination sites. The second tyrosine residue, Tyr95, is not
bound directly to the iron. The implication of these structures with respect to
the mechanism of iron binding by the transferrins is addressed.
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Figure 1.
Figure 1 A ribbon diagram of the 18 kDa fragment of duck
ovotransferrin corresponding to the NII domain. The location of
the synergistic carbonate anion and the ferric cation at the
N-terminus of the helix formed by residues 124-134, helix 5, is
clearly shown together with tyrosine residues Tyr95 and Tyr188.
The remaining ligands to the iron have been omitted (see Figs.
2-and 3-), but the exposure of the cation to the solvent is
apparent. The poorly defined loop region, 144-149, is at the
left-hand side of the diagram, immediately following helix 5.
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The above figure is
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(2002,
58,
777-783)
copyright 2002.
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