Solvent Tuning of Electrochemical Potentials in the Active Sites of HiPIP Versus Ferredoxin

A persistent puzzle in the field of biological electron transfer is the conserved iron-sulfur cluster motif in both high potential iron-sulfur protein (HiPIP) and ferredoxin (Fd) active sites. Despite this structural similarity, HiPIPs react oxidatively at physiological potentials, whereas Fds are r...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2007-11, Vol.318 (5855), p.1464-1468
Main Authors: Dey, Abhishek, Jenney, Francis E. Jr, Adams, Michael W.W, Babini, Elena, Takahashi, Yasuhiro, Fukuyama, Keiichi, Hodgson, Keith O, Hedman, Britt, Solomon, Edward I
Format: Article
Language:English
Subjects:
Active sites
Analytical, structural and metabolic biochemistry
Bacterial Proteins - chemistry
Binding Sites
Biochemistry
Biological
Biological and medical sciences
Biophysics
Chemical compounds
Covalence
Covalent bonds
Electricity
Electrochemistry
Electrode potentials
Electrostatics
Ferredoxins
Ferredoxins - chemistry
Fundamental and applied biological sciences. Psychology
Hydration
Hydrogen Bonding
Hydrophobic and Hydrophilic Interactions
Iron
Iron - chemistry
Iron-Sulfur Proteins - chemistry
Ligands
Metalloproteins
Molecules
Orbitals
Other metalloproteins
Oxidation
Oxidation-Reduction
Photosynthetic Reaction Center Complex Proteins - chemistry
Protein Folding
Proteins
Similarity
Solvents
Spectrum Analysis
Static Electricity
Sulfur
Sulfur - chemistry
Tuning
Water - chemistry
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Summary:A persistent puzzle in the field of biological electron transfer is the conserved iron-sulfur cluster motif in both high potential iron-sulfur protein (HiPIP) and ferredoxin (Fd) active sites. Despite this structural similarity, HiPIPs react oxidatively at physiological potentials, whereas Fds are reduced. Sulfur K-edge x-ray absorption spectroscopy uncovers the substantial influence of hydration on this variation in reactivity. Fe-S covalency is much lower in natively hydrated Fd active sites than in HiPIPs but increases upon water removal; similarly, HiPIP covalency decreases when unfolding exposes an otherwise hydrophobically shielded active site to water. Studies on model compounds and accompanying density functional theory calculations support a correlation of Fe-S covalency with ease of oxidation and therefore suggest that hydration accounts for most of the difference between Fd and HiPIP reduction potentials.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.1147753