title: Electrostatic influence of PsaC protein binding to the PsaA/PsaB heterodimer in photosystem I.
abstract: The absence of the PsaC subunit in the photosystem I (PSI) complex (native PSI complex) by mutagenesis or chemical manipulation yields a PSI core (P700-F(X) core) that also lacks subunits PsaD and PsaE and the two iron-sulfur clusters F(A) and F(B), which constitute an integral part of PsaC. In this P700-F(X) core, the redox potentials (E(m)) of the two quinones A(1A/B) and the iron-sulfur cluster F(X) as well as the corresponding protonation patterns are investigated by evaluating the electrostatic energies from the solution of the linearized Poisson-Boltzmann equation. The B-side specific Asp-B558 changes its protonation state significantly upon isolating the P700-F(X) core, being mainly protonated in the native PSI complex but ionized in the P700-F(X) core. In the P700-F(X) core, E(m)(A(1A/B)) remains practically unchanged, whereas E(m)(F(X)) is upshifted by 42 mV. With these calculated E(m) values, the electron transfer rate from A(1) to F(X) in the P700-F(X) core is estimated to be slightly faster on the A(1A) side than that of the wild type, which is consistent with kinetic measurements.
authors.affiliation: Institute of Chemistry and Biochemistry, Department of Biology, Free University of Berlin, D-14195 Berlin, Germany.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikita
authors.forename: Dietmar
authors.initials: D
authors.lastname: Stehlik
authors.forename: John H
authors.initials: JH
authors.lastname: Golbeck
authors.forename: Ernst-Walter
authors.initials: EW
authors.lastname: Knapp
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry; D018360:Crystallography, X-Ray; D019281:Dimerization; D004563:Electrochemistry; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000502:physiology*; D008239:Lysine / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D016296:Mutagenesis; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000502:physiology*; D010940:Plant Proteins / Q000737:chemistry / Q000502:physiology*; D016012:Poisson Distribution; D011485:Protein Binding; D011487:Protein Conformation; D055672:Static Electricity; D046940:Synechococcus / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; C089909:photosystem I, psaB subunit; D001224:Aspartic Acid; D008239:Lysine