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 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.
Dey
Abhishek
A
Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
Jenney
Francis E
FE
Adams
Michael W W
MW
Babini
Elena
E
Takahashi
Yasuhiro
Y
Fukuyama
Keiichi
K
Hodgson
Keith O
KO
Hedman
Britt
B
Solomon
Edward I
EI
D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D004563:Electrochemistry; D005288:Ferredoxins / Q000737:chemistry*; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D007501:Iron / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008024:Ligands; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D017510:Protein Folding; D012997:Solvents; D013057:Spectrum Analysis; D055672:Static Electricity; D013455:Sulfur / Q000737:chemistry; D014867:Water / Q000737:chemistry
D001426:Bacterial Proteins; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D008024:Ligands; D045322:Photosynthetic Reaction Center Complex Proteins; D012997:Solvents; C007943:high potential iron-sulfur protein; D014867:Water; D013455:Sulfur; D007501:Iron