title: The ternary complex of cytochrome f and cytochrome c: identification of a second binding site and competition for plastocyanin binding.
abstract: The complex of yeast cytochrome c and cytochrome f from the cyanobacterium Phormidium laminosum was investigated by NMR spectroscopy. Chemical shift perturbation analysis reveals that residues around the haem edge of cytochrome c are involved in the complex interface. Binding curves derived from an NMR spectroscopy titration at 10 mM ionic strength indicate that there are two sites for cytochrome c with binding constants of approximately 2 x 10(4) M(-1) and 4 x 10(3) M(-1). A protein docking simulation with NMR-derived constraints identifies two sites, at the front (Site I) and back faces (Site II) of the haem region of cytochrome f. Site I is homologous to the binding site previously determined for the natural cytochrome f partner plastocyanin. Site II may represent the binding site for the Rieske protein in the cytochrome bf complex. Cytochrome c and plastocyanin are shown to compete for binding at Site I. The competition appears to involve electrostatic screening rather than simple steric occlusion of the binding site.
mesh_terms: D000577:Amides / Q000737:chemistry; D001665:Binding Sites; D001667:Binding, Competitive; D003198:Computer Simulation; D000458:Cyanobacteria / Q000378:metabolism; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism*; D003580:Cytochromes / Q000737:chemistry / Q000378:metabolism*; D045348:Cytochromes f; D007700:Kinetics; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010970:Plastocyanin / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D055672:Static Electricity
chemical_list: D000577:Amides; D003574:Cytochrome c Group; D003580:Cytochromes; D010970:Plastocyanin; D045348:Cytochromes f