title: Species-dependent alteration of electron transfer in the early stages of charge stabilization in Photosystem I.
abstract: Electron transfer (ET) in Photosystem I (PS I) is bidirectional, occurring in two pseudosymmetric branches of cofactors. The relative use of two branches in the green alga Chlamydomonas reinhardtii and the cyanobacterium Synechocystis sp. PCC 6803 has been studied by changing the Met axial ligands of the chlorophyll a acceptor molecules, A0A and A0B, to His. The nature of the effect on the ET is found to be species dependent. In C. reinhardtii, transient absorption and transient EPR data show that in the M688HPsaA variant, forward ET from A0A to the quinone, A1A, is blocked in 100% of the PS I complexes. In contrast, in Synechocystis sp. PCC 6803, forward ET from A0A to A1A is blocked in only 50% of the PS I complexes, but in those PS I complexes in which electrons reach A1A, further transfer to the iron-sulfur cluster FX is blocked. Similar species differences are found for the corresponding B-branch variants. One possible explanation of this behavior is that it is the result of two conformers in which an H-bond between the His side chain and the O1 carbonyl group of A1 is either present or absent. The spectroscopic data suggest that the two conformers are present in nearly equal amounts in the Synechocystis sp. PCC 6803 variants, while only the conformer without the H-bond is present in the same variants of C. reinhardtii.
authors: School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA; Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287, USA; Center for Bioenergy & Photosynthesis, Arizona State University, Tempe, AZ 85287, USA.
authors: Michael D
authors: MD
authors: McConnell
authors: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors: Junlei
authors: J
authors: Sun
authors: Department of Chemistry, Brock University, St. Catharines, ON L2S 3A1, Canada.
authors: Reza
authors: R
authors: Siavashi
authors: School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA; Center for Bioenergy & Photosynthesis, Arizona State University, Tempe, AZ 85287, USA.
authors: Andrew
authors: A
authors: Webber
authors: Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287, USA; Center for Bioenergy & Photosynthesis, Arizona State University, Tempe, AZ 85287, USA. Electronic address: Kevin.Redding@asu.edu.
authors: Kevin E
authors: KE
authors: Redding
authors: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA; Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA. Electronic address: jhg5@psu.edu.
authors: John H
authors: JH
authors: Golbeck
authors: Department of Chemistry, Brock University, St. Catharines, ON L2S 3A1, Canada. Electronic address: avde@brocku.ca.
authors: Art
authors: A
authors: van der Est
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000737:chemistry* / Q000235:genetics / Q000254:growth & development; D002734:Chlorophyll / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000737:chemistry* / Q000235:genetics / Q000254:growth & development; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D006639:Histidine / Q000235:genetics; D006860:Hydrogen Bonding; D007700:Kinetics; D008715:Methionine / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D013696:Temperature
chemical_list: D045331:Photosystem I Protein Complex; D002734:Chlorophyll; D006639:Histidine; D008715:Methionine; D000077194:Chlorophyll A
keywords: A(0); Electron transfer; Photosynthesis; Photosystem I; Phylloquinone