title: Site-directed mutations affecting the spectroscopic characteristics and midpoint potential of the primary donor in photosystem I.
abstract: Photosystem I is a member of the iron-sulfur center or type I reaction centers. The primary electron donor in photosystem I is a chlorophyll a dimer termed P700. The biophysical properties of P700 are well understood, but the protein environment that gives it such unique properties is unknown. We have characterized site-directed mutants of the photosystem I reaction center protein PsaB and identified an amino acid, His-656, that interacts closely with one of the P700 chlorophylls. Mutation of His-656 to Asn or Ser increases the oxidation midpoint potential of P700/P700+. by 40 mV. The P700/P700+. optical difference spectra show the appearance of a new bleaching band at 667 nm. Electron nuclear double resonance spectroscopy indicates a significant increase in the hyperfine coupling corresponding to methyl protons at position 12 of the spin carrying chlorophyll a of P700+. The implication of these results to current structural models of the photosystem I reaction center is discussed.
authors.affiliation: Department of Botany, Arizona State University, Tempe 85287-1601, USA. andrew.webber@asu.edu
authors.forename: A N
authors.initials: AN
authors.lastname: Webber
authors.forename: H
authors.initials: H
authors.lastname: Su
authors.forename: S E
authors.initials: SE
authors.lastname: Bingham
authors.forename: H
authors.initials: H
authors.lastname: Käss
authors.forename: L
authors.initials: L
authors.lastname: Krabben
authors.forename: M
authors.initials: M
authors.lastname: Kuhn
authors.forename: R
authors.initials: R
authors.lastname: Jordan
authors.forename: E
authors.initials: E
authors.lastname: Schlodder
authors.forename: W
authors.initials: W
authors.lastname: Lubitz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000737:chemistry / Q000235:genetics; D002734:Chlorophyll / Q000737:chemistry* / Q000235:genetics; D000077194:Chlorophyll A; D002736:Chloroplasts / Q000737:chemistry / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D006639:Histidine / Q000737:chemistry / Q000235:genetics; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D045331:Photosystem I Protein Complex; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013053:Spectrophotometry
chemical_list: D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; C089909:photosystem I, psaB subunit; D002734:Chlorophyll; D006639:Histidine; C001785:chlorophyll P 700; D000077194:Chlorophyll A