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Title: Computational Approach for Probing Redox Potential for Iron-Sulfur Clusters in Photosystem I

Journal Article · · Biology
ORCiD logo [1];  [2]; ORCiD logo [3]
  1. Helwan University, Cairo (Egypt); University of Tennessee, Knoxville, TN (United States); Univ. of Groningen (Netherlands)
  2. Helwan University, Cairo (Egypt)
  3. University of Groningen (Netherlands); City University of New York (CUNY), NY (United States)

Photosystem I is a light-driven electron transfer device. Available X-ray crystal structure from Thermosynechococcus elongatus showed that electron transfer pathways consist of two nearly symmetric branches of cofactors converging at the first iron–sulfur cluster FX, which is followed by two terminal iron–sulfur clusters FA and FB. Experiments have shown that FX has lower oxidation potential than FA and FB, which facilitates the electron transfer reaction. Here, we use density functional theory and Multi-Conformer Continuum Electrostatics to explain the differences in the midpoint Em potentials of the FX, FA and FB clusters. Our calculations show that FX has the lowest oxidation potential compared to FA and FB due to strong pairwise electrostatic interactions with surrounding residues. These interactions are shown to be dominated by the bridging sulfurs and cysteine ligands, which may be attributed to the shorter average bond distances between the oxidized Fe ion and ligating sulfurs for FX compared to FA and FB. Moreover, the electrostatic repulsion between the 4Fe-4S clusters and the positive potential of the backbone atoms is lowest for FX compared to both FA and FB. These results agree with the experimental measurements from the redox titrations of low-temperature EPR signals and of room temperature recombination kinetics.

Research Organization:
City University of New York (CUNY), NY (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
SC0001423
OSTI ID:
1981111
Journal Information:
Biology, Journal Name: Biology Journal Issue: 3 Vol. 11; ISSN 2079-7737
Publisher:
MDPICopyright Statement
Country of Publication:
United States
Language:
English

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