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PDBsum entry 1axx
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Electron transport
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PDB id
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1axx
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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 solution structure of oxidized rat microsomal cytochrome b5.
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Authors
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F.Arnesano,
L.Banci,
I.Bertini,
I.C.Felli.
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Ref.
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Biochemistry, 1998,
37,
173-184.
[DOI no: ]
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PubMed id
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Abstract
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The solution structure of oxidized rat microsomal cytochrome b5 has been
obtained from 1H NMR spectra measured at 800 MHz. The available assignment has
been extended to 78% of the total protons and 95% of the residues. From 1372
meaningful NOEs, a family of 40 structures has been obtained through the program
DYANA; 235 pseudocontact shifts have been then added as further constraints,
obtaining an essentially similar family of structures. This latter family has
been further refined through restrained energy minimization. The final RMSD
values with respect to the average structure are 0.58 +/- 0.10 A and 1.05 +/-
0.11 A for backbone and heavy atoms, respectively. The high quality of the
structure allows meaningful comparisons with the solution structure of the
reduced protein, with the X-ray and solution structures of the oxidized bovine
isoenzyme, and with the solution structure of the apoprotein. Upon loss of one
electron, the heme plane undergoes a change in its orientation, possibly due to
the change of the total charge. Propionate 7 appears to have a conformation
which is dependent on the oxidation state of the iron. Helices alpha2 and alpha4
also experience changes in their average positions in the two oxidation states.
Finally, the backbone NHs experience different exchange properties in the two
oxidation states. While those present in the beta sheets forming the basis of
the heme pocket are nonexchanging in both oxidation states, the NHs in the
helices forming the heme-binding pocket are exchanging with the bulk solvent in
the oxidized form, indicating larger local mobility in this state. This
observation could suggest that, to optimize the electron transfer process, the
local mobility should be properly tuned.
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