title: Loss of electrostatic interactions causes increase of dynamics within the plastocyanin-cytochrome f complex.
abstract: Recent studies on the electron transfer complex formed by cytochrome f and plastocyanin from Nostoc revealed that both hydrophobic and electrostatic interactions play a role in the process of complex formation. To study the balance between these two types of interactions in the encounter and the final state, the complex between plastocyanin from Phormidium laminosum and cytochrome f from Nostoc sp. PCC 7119 was investigated using NMR spectroscopy and Monte Carlo docking. Cytochrome f has a highly negative charge. Phormidium plastocyanin is similar to that from Nostoc, but the net charge of the protein is negative rather than positive. NMR titrations of Zn-substituted Phormidium plastocyanin and Nostoc cytochrome f indicated that a complex with an affinity intermediate between those of the Nostoc and Phormidium complexes is formed. Plastocyanin was found in a head-on orientation, as determined using pseudocontact shifts, similar to that in the Phormidium complex, in which the hydrophobic patch represents the main site of interaction on plastocyanin. However, the interaction in the cross-complex is dependent on electrostatics, similar to that in the Nostoc complex. The negative charge of plastocyanin decreases, but not abolishes, the attraction to cytochrome f, resulting in the formation of a more diffuse encounter complex than in the Nostoc case, as could be determined using paramagnetic relaxation spectroscopy. This work illustrates the subtle interplay of electrostatic and hydrophobic interactions in the formation of transient protein complexes. The results are discussed in the context of a model for association on the basis of hydrophobic contacts in the encounter state.
authors.affiliation: Institute of Chemistry, Leiden University , Einsteinweg 55, 2333 CC Leiden, The Netherlands.
authors.forename: Sandra
authors.initials: S
authors.lastname: Scanu
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Foerster
authors.forename: Monika
authors.initials: M
authors.lastname: Timmer
authors.forename: G Matthias
authors.initials: GM
authors.lastname: Ullmann
authors.forename: Marcellus
authors.initials: M
authors.lastname: Ubbink
mesh_terms: D045348:Cytochromes f / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D062105:Molecular Docking Simulation; D009010:Monte Carlo Method; D046937:Nostoc / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010970:Plastocyanin / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D010970:Plastocyanin; D045348:Cytochromes f