title: The dynamic complex of cytochrome c6 and cytochrome f studied with paramagnetic NMR spectroscopy.
abstract: The rapid transfer of electrons in the photosynthetic redox chain is achieved by the formation of short-lived complexes of cytochrome b6f with the electron transfer proteins plastocyanin and cytochrome c6. A balance must exist between fast intermolecular electron transfer and rapid dissociation, which requires the formation of a complex that has limited specificity. The interaction of the soluble fragment of cytochrome f and cytochrome c6 from the cyanobacterium Nostoc sp. PCC 7119 was studied using NMR spectroscopy and X-ray diffraction. The crystal structures of wild type, M58H and M58C cytochrome c6 were determined. The M58C variant is an excellent low potential mimic of the wild type protein and was used in chemical shift perturbation and paramagnetic relaxation NMR experiments to characterize the complex with cytochrome f. The interaction is highly dynamic and can be described as a pure encounter complex, with no dominant stereospecific complex. Ensemble docking calculations and Monte-Carlo simulations suggest a model in which charge-charge interactions pre-orient cytochrome c6 with its haem edge toward cytochrome f to form an ensemble of orientations with extensive contacts between the hydrophobic patches on both cytochromes, bringing the two haem groups sufficiently close to allow for rapid electron transfer. This model of complex formation allows for a gradual increase and decrease of the hydrophobic interactions during association and dissociation, thus avoiding a high transition state barrier that would slow down the dissociation process.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain. Electronic address: idiazmoreno@us.es.
authors.forename: Irene
authors.initials: I
authors.lastname: Díaz-Moreno
authors.affiliation: Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands. Electronic address: hulsker_rinske@yahoo.co.uk.
authors.forename: Rinske
authors.initials: R
authors.lastname: Hulsker
authors.affiliation: Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands. Electronic address: p.skubak@chem.leidenuniv.nl.
authors.forename: Pavol
authors.initials: P
authors.lastname: Skubak
authors.affiliation: Computational Biochemistry, University of Bayreuth, Universitätsstrasse 30, 95447 Bayreuth, Germany. Electronic address: johannes.foerster@uni-bayreuth.de.
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Foerster
authors.affiliation: Department of Life Sciences, Laboratory of Biochemistry, Molecular Biology and Bioinformatics, Parco Area delle Scienze 23/a, University of Parma, 43124 Parma, Italy. Electronic address: davide.cavazzini@unipr.it.
authors.forename: Davide
authors.initials: D
authors.lastname: Cavazzini
authors.affiliation: Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands. Electronic address: mfinig@hotmail.com.
authors.forename: Michelina G
authors.initials: MG
authors.lastname: Finiguerra
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain. Electronic address: qzaida@us.es.
authors.forename: Antonio
authors.initials: A
authors.lastname: Díaz-Quintana
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain. Electronic address: joseblas.moreno@ibvf.csic.es.
authors.forename: Blas
authors.initials: B
authors.lastname: Moreno-Beltrán
authors.affiliation: Department of Life Sciences, Laboratory of Biochemistry, Molecular Biology and Bioinformatics, Parco Area delle Scienze 23/a, University of Parma, 43124 Parma, Italy. Electronic address: gianluigi.rossi@unipr.it.
authors.forename: Gian-Luigi
authors.initials: GL
authors.lastname: Rossi
authors.affiliation: Computational Biochemistry, University of Bayreuth, Universitätsstrasse 30, 95447 Bayreuth, Germany. Electronic address: Matthias.Ullmann@uni-bayreuth.de.
authors.forename: G Matthias
authors.initials: GM
authors.lastname: Ullmann
authors.affiliation: Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands. Electronic address: raj@chem.leidenuniv.nl.
authors.forename: Navraj S
authors.initials: NS
authors.lastname: Pannu
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain. Electronic address: marosa@us.es.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: De la Rosa
authors.affiliation: Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands. Electronic address: m.ubbink@chem.leidenuniv.nl.
authors.forename: Marcellus
authors.initials: M
authors.lastname: Ubbink
mesh_terms: D000458:Cyanobacteria / Q000737:chemistry / Q000378:metabolism; D045365:Cytochromes c6 / Q000737:chemistry* / Q000378:metabolism; D045348:Cytochromes f / Q000737:chemistry* / Q000378:metabolism; D004579:Electron Transport; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D009010:Monte Carlo Method; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D010788:Photosynthesis; D010970:Plastocyanin / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D060066:Protein Interaction Maps; D014961:X-Ray Diffraction
chemical_list: D045365:Cytochromes c6; D046912:Multiprotein Complexes; D010970:Plastocyanin; D045348:Cytochromes f
keywords: Crystallography; Electron transfer; Monte-Carlo modelling; Paramagnetic relaxation enhancement; Photosynthesis; Protein interaction