title: Evidence that histidine forms a coordination bond to the A(0A) and A(0B) chlorophylls and a second H-bond to the A(1A) and A(1B) phylloquinones in M688H(PsaA) and M668H(PsaB) variants of Synechocystis sp. PCC 6803.
abstract: The axial ligands of the acceptor chlorophylls, A(0A) and A(0B), in Photosystem I are the Met sulfur atoms of M688(PsaA) and M668(PsaB). To determine the role of the Met, His variants were generated in Synechocystis sp. PCC 6803. Molecular dynamics simulations on M688H(PsaA) show that there exist low energy conformations with the His coordinated to A(0A) and possibly H-bonded to A(1A). Transient EPR studies on M688H(PsaA) indicate a more symmetrical electron spin distribution in the A(1A) phyllosemiquinone ring consistent with the presence of an H-bond to the C1 carbonyl. Ultrafast optical studies on the variants show that the 150fs charge separation between P₇₀₀ and A(0) remains unaffected. Studies on the ns timescale show that 57% of the electrons are transferred from A(0A)(-) to A(1A) in M688H(PsaA) and 48% from A(0B)(-) to A(1B) in M668H(PsaB); the remainder recombine with P₇₀₀(+) with 1/e times of 25ns and 37ns, respectively. Those electrons that reach A(1A) and A(1B) in the branch carrying the mutation are not transferred to FX, but recombine with P₇₀₀(+) with 1/e times of ~15μs and ~5μs, respectively. Hence, the His is coordinated to A0 in all populations, but in a second population, the His may be additionally H-bonded to A(1). Electron transfer from A(0) to A(1) occurs only in the latter, but the higher redox potentials of A(0) and A(1) as a result of the stronger coordination bond to A(0) and the proposed second H-bond to A(1) preclude electron transfer to the Fe/S clusters.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Junlei
authors.initials: J
authors.lastname: Sun
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Sijie
authors.initials: S
authors.lastname: Hao
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Radle
authors.affiliation: Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA.
authors.forename: Wu
authors.initials: W
authors.lastname: Xu
authors.affiliation: Department of Molecular and Chemical Physics, Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region 141700, Russian Federation.
authors.forename: Ivan
authors.initials: I
authors.lastname: Shelaev
authors.affiliation: Department of Molecular and Chemical Physics, Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region 141700, Russian Federation.
authors.forename: Victor
authors.initials: V
authors.lastname: Nadtochenko
authors.affiliation: A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow 119991, Russia.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shuvalov
authors.affiliation: A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow 119991, Russia.
authors.forename: Alexey
authors.initials: A
authors.lastname: Semenov
authors.affiliation: Department of Chemistry, Brock University, St. Catharines, ON, Canada L2S 3A1.
authors.forename: Heather
authors.initials: H
authors.lastname: Gordon
authors.affiliation: Department of Chemistry, Brock University, St. Catharines, ON, Canada L2S 3A1. Electronic address: avde@brocku.ca.
authors.forename: Art
authors.initials: A
authors.lastname: van der Est
authors.affiliation: 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.forename: John H
authors.initials: JH
authors.lastname: Golbeck
mesh_terms: D002734:Chlorophyll / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D006639:Histidine; D006860:Hydrogen Bonding; D007700:Kinetics; D008024:Ligands; D009154:Mutation; D010788:Photosynthesis / Q000235:genetics*; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000235:genetics; D046939:Synechocystis / Q000737:chemistry / Q000235:genetics* / Q000254:growth & development
chemical_list: D008024:Ligands; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; D006639:Histidine
keywords: A(0); A(1); Chlorophyll a; Photosynthesis; Photosystem I; Phylloquinone