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.
Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
Abhishek
A
Dey
Francis E
FE
Jenney
Michael W W
MW
Adams
Elena
E
Babini
Yasuhiro
Y
Takahashi
Keiichi
K
Fukuyama
Keith O
KO
Hodgson
Britt
B
Hedman
Edward I
EI
Solomon
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