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PDBsum entry 2fl0
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Metal binding protein
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PDB id
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2fl0
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References listed in PDB file
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Key reference
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Title
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Redox-Dependent structural changes in the azotobacter vinelandii bacterioferritin: new insights into the ferroxidase and iron transport mechanism.
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Authors
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L.Swartz,
M.Kuchinskas,
H.Li,
T.L.Poulos,
W.N.Lanzilotta.
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Ref.
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Biochemistry, 2006,
45,
4421-4428.
[DOI no: ]
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PubMed id
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Abstract
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In this work, we report the X-ray crystal structure of the aerobically isolated
(oxidized) and the anaerobic dithionite-reduced (at pH 8.0) forms of the native
Azotobacter vinelandii bacterioferritin to 2.7 and 2.0 A resolution,
respectively. Iron K-edge multiple anomalous dispersion (MAD) experiments
unequivocally identified the presence of three independent iron-containing sites
within the protein structure. Specifically, a dinuclear (ferroxidase) site, a
b-type heme site, and the binding of a single iron atom at the four-fold
molecular axis of the protein shell were observed. In addition to the novel
observation of iron at the four-fold pore, these data also reveal that the
oxidized form of the protein has a symmetrical ferroxidase site containing two
five-coordinate iron atoms. Each iron atom is ligated by four carboxylate oxygen
atoms and a single histidyl nitrogen atom. A single water molecule is found
within hydrogen bonding distance of the ferroxidase site that bridges the two
iron atoms on the side opposite the histidine ligands. Chemical reduction of the
protein under anaerobic conditions results in an increase in the average Fe-Fe
distance in the ferroxidase site from approximately 3.5 to approximately 4.0 A
and the loss of one of the ligands, H130. In addition, there is significant
movement of the bridging water molecule and several other amino acid side chains
in the vicinity of the ferroxidase site and along the D helix to the three-fold
symmetry axis. In contrast to previous work, the higher-resolution data for the
dithionite-reduced structure suggest that the heme may be bound in multiple
conformations. Taken together, these data allow a molecular movie of the
ferroxidase gating mechanism to be developed and provide further insight into
the iron uptake and/or release and mineralization mechanism of bacterioferritins
in general.
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