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PDBsum entry 1a8f
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Iron transport
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PDB id
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1a8f
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References listed in PDB file
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Key reference
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Title
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Two high-Resolution crystal structures of the recombinant n-Lobe of human transferrin reveal a structural change implicated in iron release.
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Authors
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R.T.Macgillivray,
S.A.Moore,
J.Chen,
B.F.Anderson,
H.Baker,
Y.Luo,
M.Bewley,
C.A.Smith,
M.E.Murphy,
Y.Wang,
A.B.Mason,
R.C.Woodworth,
G.D.Brayer,
E.N.Baker.
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Ref.
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Biochemistry, 1998,
37,
7919-7928.
[DOI no: ]
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PubMed id
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Abstract
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The N-lobe of human serum transferrin (hTF/2N) has been expressed in baby
hamster kidney cells and crystallized in both orthorhombic (P212121) and
tetragonal (P41212) space groups. Both crystal forms diffract to high resolution
(1.6 and 1.8 A, respectively) and have been solved by molecular replacement.
Subsequent refinement resulted in final models for the structure of hTF/2N that
had crystallographic R-factors of 18.1 and 19.7% for the two crystal forms,
respectively; these models represent the highest-resolution transferrin
structures determined to date. The hTF/2N polypeptide has a folding pattern
similar to those of other transferrins, including the presence of a deep cleft
that contains the metal-binding site. In contrast to other transferrins, both
crystal forms of hTF/2N display disorder at the iron-binding site; model
building suggests that this disorder consists of alternative conformations of
the synergistically bound carbonate anion, the side chain for Arg-124, and
several solvent molecules. Subsequent refinement revealed that conformation A
has an occupancy of 0.63-0. 65 and corresponds to the structure of the
iron-binding site found in other transferrins. The alternative conformation B
has an occupancy of 0.35-0.37; in this structure, the carbonate has rotated 30
degrees relative to the iron and the side chain for Arg-124 has moved to
accommodate the new carbonate position. Several water molecules appear to
stabilize the carbonate anion in the two conformations. These structures are
consistent with the protonation of the carbonate and resulting partial removal
of the anion from the metal; these events would occur prior to cleft opening and
metal release.
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