title: Gallium ferredoxin as a tool to study the effects of ferredoxin binding to photosystem I without ferredoxin reduction.
abstract: Reduction of ferredoxin by photosystem I (PSI) involves the [4Fe-4S] clusters FAand FBharbored by PsaC, with FBbeing the direct electron transfer partner of ferredoxin (Fd). Binding of the redox-inactive gallium ferredoxin to PSI was investigated by flash-absorption spectroscopy, studying both the P700+decay and the reduction of the native iron Fd in the presence of FdGa. FdGabinding resulted in a faster recombination between P700+and (FA, FB)-, a slower electron escape from (FA, FB)-to exogenous acceptors, and a decreased amount of intracomplex FdFereduction, in accordance with competitive binding between FdFeand FdGa. [FdGa] titrations of these effects revealed that the dissociation constant for the PSI:FdGacomplex is different whether (FA, FB) is oxidized or singly reduced. This difference in binding, together with the increase in the recombination rate, could both be attributed to a c. -30 mV shift of the midpoint potential of (FA, FB), considered as a single electron acceptor, due to FdGabinding. This effect of FdGabinding, which can be extrapolated to FdFebecause of the highly similar structure and the identical charge of the two Fds, should help irreversibility of electron transfer within the PSI:Fd complex. The effect of Fd binding on the individual midpoint potentials of FAand FBis also discussed with respect to the possible consequences on intra-PSI electron transfer and on the escape process.
authors.affiliation: Institut de Biologie Intégrative de la Cellule (I2BC), IBITECS, CEA, CNRS, Univ. Paris-Saclay, F-91198, Gif-sur-Yvette cedex, France.
authors.forename: Clara
authors.initials: C
authors.lastname: Mignée
authors.affiliation: Institute for Protein Research, Osaka University, Suita, Osaka, 565-0871, Japan.
authors.forename: Risa
authors.initials: R
authors.lastname: Mutoh
authors.affiliation: Institut de Biologie Intégrative de la Cellule (I2BC), IBITECS, CEA, CNRS, Univ. Paris-Saclay, F-91198, Gif-sur-Yvette cedex, France.
authors.forename: Anja
authors.initials: A
authors.lastname: Krieger-Liszkay
authors.affiliation: Institute for Protein Research, Osaka University, Suita, Osaka, 565-0871, Japan.
authors.forename: Genji
authors.initials: G
authors.lastname: Kurisu
authors.affiliation: Institut de Biologie Intégrative de la Cellule (I2BC), IBITECS, CEA, CNRS, Univ. Paris-Saclay, F-91198, Gif-sur-Yvette cedex, France. pierre.setif@cea.fr.
authors.forename: Pierre
authors.initials: P
authors.lastname: Sétif
mesh_terms: D001665:Binding Sites; D004583:Electrons; D005288:Ferredoxins / Q000378:metabolism*; D005708:Gallium / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D011485:Protein Binding; D013816:Thermodynamics
chemical_list: D005288:Ferredoxins; D045331:Photosystem I Protein Complex; D005708:Gallium
keywords: Cyanobacteria; Electron escape; Electron transfer; Ferredoxin binding; Photosynthesis; Photosystem I inhibitor; Recombination reaction; Redox potential