Negatively charged residues in the H loop of PsaB subunit in Photosystem I from Synechocystis sp. PCC 6803 appear to be responsible for electrostatic repulsions with plastocyanin* |
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Authors: | Navarro José A. Hervás Manuel Sun Jun De la Cerda Berta Chitnis Parag R. De la Rosa Miguel A. |
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Affiliation: | (1) Instituto de Bioquímica Vegetal y Fotosíntesis, Centro Isla de la Cartuja, Américo Vespucio s/n, 41092 Sevilla, Spain;(2) Department of Biochemistry and Biophysics, Iowa State University, Ames, IA 50011, USA;(3) Department of Biochemistry and Biophysics, Iowa State University, Ames, IA 50011, USA |
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Abstract: | ![]() Wild-type plastocyanin from the cyanobacterium Synechocystis sp. PCC 6803 does not form any kinetically detectable transient complex with Photosystem I (PS I) during electron transfer, but the D44R/D47R double mutant of copper protein does [De la Cerda et al. (1997) Biochemistry 36: 10125–10130]. To identify the PS I component that is involved in the complex formation with the D44R/D47R plastocyanin, the kinetic efficiency of several PS I mutants, including a PsaF–PsaJ-less PS I and deletion mutants in the lumenal H and J loops of PsaB, were analyzed by laser flash absorption spectroscopy. The experimental data herein suggest that some of the negative charges at the H loop of PsaB are involved in electrostatic repulsions with mutant plastocyanin. Mutations in the J loop demonstrate that this region of PsaB is also critical. The interaction site of PS I is thus not as defined as first expected but much broader, thereby revealing how complex the evolution of intermolecular electron transfer mechanisms in photosynthesis has been. This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | cytochrome c 6 electron transfer Photosystem I plastocyanin site-directed mutagenesis Synechocystis |
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