Iron–sulfur clusters in type I reaction centers

• Published in: BBA - Bioenergetics Vol. 1507; no. 1; pp. 139 - 160
• Main Authors: Vassiliev, Ilya R., Antonkine, Mikhail L., Golbeck, John H.
• Format: Book Review Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 30-10-2001
• Subjects: Charge recombination; Chlorobi - chemistry; Cyanobacteria - chemistry; Electron paramagnetic resonance (EPR); Electron Spin Resonance Spectroscopy; Electron transfer; Electron Transport; Equilibrium; F A; F B; F X; Iron-Sulfur Proteins - chemistry; Iron–sulfur cluster; Kinetics; Light-Harvesting Protein Complexes; Magnetic Resonance Spectroscopy; Membrane Proteins; Models, Molecular; Molecular Structure; Nuclear magnetic resonance (NMR); Photosynthetic Reaction Center Complex Proteins - chemistry; Photosystem I; Photosystem I Protein Complex; Proteins - chemistry; PsaC; RC, reaction center; PsaC; F A; Photosystem I; Electron transfer; Charge recombination; F B; E m, midpoint potential; F B, [4Fe–4S] cluster bound by cysteines 11, 14, 17 and 58 of the PsaC subunit of Photosystem I; F X, [4Fe–4S] cluster bound to the PsaA and PsaB subunits of Photosystem I; Equilibrium; F A, [4Fe–4S] cluster bound by cysteines 21, 48, 51 and 54 of the PsaC subunit of Photosystem I; Chl, chlorophyll; ΔA 820, absorbance change at 820 nm; Iron–sulfur cluster; β-ME, β-mercaptoethanol; Electron paramagnetic resonance (EPR); Kinetics; DCPIP, 2,6-dichlorophenol-indophenol; PS I, Photosystem I; PMS, phenazine methosulfate; Nuclear magnetic resonance (NMR); F X
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/S0005-2728(01)00197-9

Type I reaction centers (RCs) are multisubunit chlorophyll–protein complexes that function in photosynthetic organisms to convert photons to Gibbs free energy. The unique feature of Type I RCs is the presence of iron–sulfur clusters as electron transfer cofactors. Photosystem I (PS I) of oxygenic phototrophs is the best-studied Type I RC. It is comprised of an interpolypeptide [4Fe–4S] cluster, F
X, that bridges the PsaA and PsaB subunits, and two terminal [4Fe–4S] clusters, F
A and F
B, that are bound to the PsaC subunit. In this review, we provide an update on the structure and function of the bound iron–sulfur clusters in Type I RCs. The first new development in this area is the identification of F
A as the cluster proximal to F
X and the resolution of the electron transfer sequence as F
X→F
A→F
B→soluble ferredoxin. The second new development is the determination of the three-dimensional NMR solution structure of unbound PsaC and localization of the equal- and mixed-valence pairs in F
A
− and F
B
−. We provide a survey of the EPR properties and spectra of the iron–sulfur clusters in Type I RCs of cyanobacteria, green sulfur bacteria, and heliobacteria, and we summarize new information about the kinetics of back-reactions involving the iron–sulfur clusters.