title: The structure of genetically modified iron-sulfur cluster F(x) in photosystem I as determined by X-ray absorption spectroscopy.
abstract: Photosystem I (PS I) mediates light-induced electron transfer from P700 through a chlorophyll a, a quinone and a [4Fe-4S] iron-sulfur cluster F(X), located on the core subunits PsaA/B to iron-sulfur clusters F(A/B) on subunit PsaC. Structure function relations in the native and in the mutant (psaB-C565S/D566E) of the cysteine ligand of F(X) cluster were studied by X-ray absorption spectroscopy (EXAFS) and transient spectroscopy. The structure of F(X) was determined in PS I lacking clusters F(A/B) by interruption of the psaC2 gene of PS I in the cyanobacterium Synechocystis sp PCC 6803. PsaC-deficient mutant cells assembled the core subunits of PS I which mediated electron transfer mostly to the phylloquinone. EXAFS analysis of the iron resolved a [4Fe-4S] cluster in the native PsaC-deficient PS I. Each iron had 4 sulfur and 3 iron atoms in the first and second shells with average Fe-S and Fe-Fe distances of 2.27 A and 2.69 A, respectively. In the C565S/D566E serine mutant, one of the irons of the cluster was ligated to three oxygen atoms with Fe-O distance of 1.81 A. The possibility that the structural changes induced an increase in the reorganization energy that consequently decreased the rate of electron transfer from the phylloquinone to F(X) is discussed.
authors.affiliation: Department of Biochemistry, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Xiao-Min
authors.initials: XM
authors.lastname: Gong
authors.forename: Yehoshua
authors.initials: Y
authors.lastname: Hochman
authors.forename: Tal
authors.initials: T
authors.lastname: Lev
authors.forename: Grant
authors.initials: G
authors.lastname: Bunker
authors.forename: Chanoch
authors.initials: C
authors.lastname: Carmeli
mesh_terms: D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000378:metabolism*; D004579:Electron Transport; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D011487:Protein Conformation; D013052:Spectrometry, X-Ray Emission; D020524:Thylakoids
chemical_list: D007506:Iron-Sulfur Proteins; D045331:Photosystem I Protein Complex