title: Cytochrome c1 exhibits two binding sites for cytochrome c in plants.
abstract: In plants, channeling of cytochrome c molecules between complexes III and IV has been purported to shuttle electrons within the supercomplexes instead of carrying electrons by random diffusion across the intermembrane bulk phase. However, the mode plant cytochrome c behaves inside a supercomplex such as the respirasome, formed by complexes I, III and IV, remains obscure from a structural point of view. Here, we report ab-initio Brownian dynamics calculations and nuclear magnetic resonance-driven docking computations showing two binding sites for plant cytochrome c at the head soluble domain of plant cytochrome c1, namely a non-productive (or distal) site with a long heme-to-heme distance and a functional (or proximal) site with the two heme groups close enough as to allow electron transfer. As inferred from isothermal titration calorimetry experiments, the two binding sites exhibit different equilibrium dissociation constants, for both reduced and oxidized species, that are all within the micromolar range, thus revealing the transient nature of such a respiratory complex. Although the docking of cytochrome c at the distal site occurs at the interface between cytochrome c1 and the Rieske subunit, it is fully compatible with the complex III structure. In our model, the extra distal site in complex III could indeed facilitate the functional cytochrome c channeling towards complex IV by building a "floating boat bridge" of cytochrome c molecules (between complexes III and IV) in plant respirasome.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, cicCartuja, Universidad de Sevilla - CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain.
authors.forename: Blas
authors.initials: B
authors.lastname: Moreno-Beltrán
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, cicCartuja, Universidad de Sevilla - CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Díaz-Quintana
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, cicCartuja, Universidad de Sevilla - CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain.
authors.forename: Katiuska
authors.initials: K
authors.lastname: González-Arzola
authors.affiliation: Institute of Biocomputation and Physics of Complex Systems (BIFI)-Joint Unit BIFI-IQFR (CSIC), Universidad de Zaragoza, Mariano Esquillor s/n, 50018, Zaragoza, Spain; Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain; Fundacion ARAID, Government of Aragon, Maria de Luna 11, 50018, Zaragoza, Spain.
authors.forename: Adrián
authors.initials: A
authors.lastname: Velázquez-Campoy
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, cicCartuja, Universidad de Sevilla - CSIC, Avda. Américo Vespucio 49, Sevilla 41092, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: De la Rosa
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, cicCartuja, 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
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D003575:Cytochromes c1 / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D009682:Magnetic Resonance Spectroscopy; D062105:Molecular Docking Simulation; D016297:Mutagenesis, Site-Directed; D010944:Plants / Q000201:enzymology*; D016133:Polymerase Chain Reaction; D014461:Ultracentrifugation
chemical_list: D017931:DNA Primers; D003575:Cytochromes c1
keywords: Arabidopsis thaliana; Cytochrome bc(1) complex; Cytochrome c; NMR; Respirasome; Supercomplex