Ubbink group: Research: Cytochrome c6 & cytochrome f

In the photosynthetic redox chain of cyanobacteria and some green algae, plastocyanin is not always the electron acceptor for cytochrome f in the cytochrome b ₆f complex. Instead cytochrome c ₆ can take over this role. We have studied the interaction between the cytochromes c ₆ from the cyanobacteria Anabaena and Synechococcus with the cytochrome f from the cyanobacterium Phormidium laminosum . Synochococcus cytochrome c ₆ does not form any complex with cytochrome f , while Anabaena cytochrome c ₆ forms a well-defined complex with a dissociation constant of about 0.1 mM (Figure 1). In the physiological complex of cytochrome c ₆ and cytochrome f from Nostoc , chemical shift perturbation analysis shows that the binding site is localized around the haem edge and consists of a hydrophobic centre with a hydrophilic periphery, similar to the binding site on plastocyanin. A model of the complex is shown in Fig. 3.
Figure 1 ->. Binding curves for amides of Anabaena cytochrome c ₆ when titrating with (A) or into (B) Phormidium cytochrome f solution. Fitted to a 1:1 binding model with a dissociation constant of 0.1 mM. Crowley et al. (2002) Biol. Chem. 277, 48685-48689
Figure 2. Chemical shift perturbation map of Nostoc cytochrome c ₆for binding to cytochrome f . Shifts increase: cream < orange < red. The haem is in green. Grey represent missing data. Díaz-Moreno et al. (2005) FEBS Lett. 579, 2891-2896
Figure 3 ->. Model of the complex of Nostoc cytochrome c ₆for binding to cytochrome f . Díaz-Moreno et al. (2005) FEBS Lett. 579, 2891-2896