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PDBsum entry 2pt2
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Metal transport
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PDB id
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2pt2
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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 structure of the iron-Binding protein, Futa1, From synechocystis 6803.
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Authors
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N.Koropatkin,
A.M.Randich,
M.Bhattacharyya-Pakrasi,
H.B.Pakrasi,
T.J.Smith.
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Ref.
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J Biol Chem, 2007,
282,
27468-27477.
[DOI no: ]
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PubMed id
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Abstract
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Cyanobacteria account for a significant percentage of aquatic primary
productivity even in areas where the concentrations of essential micronutrients
are extremely low. To better understand the mechanism of iron selectivity and
transport, the structure of the solute binding domain of an ATP binding cassette
iron transporter, FutA1, was determined in the presence and absence of iron. The
iron ion is bound within the "C-clamp" structure via four tyrosine and
one histidine residues. There are extensive interactions between these ligating
residues and the rest of the protein such that the conformations of the side
chains remain relatively unchanged as the iron is released by the opening of the
metal binding cleft. This is in stark contrast to the zinc-binding protein,
ZnuA, where the domains of the metal-binding protein remain relatively fixed,
whereas the ligating residues rotate out of the binding pocket upon metal
release. The rotation of the domains in FutA1 is facilitated by two flexible
beta-strands running along the back of the protein that act like a hinge during
domain motion. This motion may require relatively little energy since total
contact area between the domains is the same whether the protein is in the open
or closed conformation. Consistent with the pH dependence of iron binding, the
main trigger for iron release is likely the histidine in the iron-binding site.
Finally, neither FutA1 nor FutA2 binds iron as a siderophore complex or in the
presence of anions, and both preferentially bind ferrous over ferric ions.
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Figure 2.
FIGURE 2. The iron-binding environment in FutA1. The top
stereo figure shows the electron density of iron bound to FutA1
and some of the contact residues, and the bottom stereo figure
shows some of the secondary shell contacts with the ligating
residues. The orientation here is similar to that in Fig. 1 with
the N-terminal domain toward the bottom of the figure and
looking into the iron binding pocket.
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Figure 4.
FIGURE 4. Changes in the iron-binding site upon iron
release. In this stereo figure the ligating residues in the iron
bound FutA1 structure are represented by the transparent stick
figures, and the apo form is represented by the solid structure.
The two structures were aligned according to the N-terminal
domain using the program MolView X (34).
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2007,
282,
27468-27477)
copyright 2007.
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