Protein engineering to study the interaction between Ferredoxin NADP+ reductase and Feredoxin (or Flavodoxin)
Carlos Gómez-Moreno, Isabel Nogues, Milagros Medina


Ferredoxin NADP+ reductase (FNR) is a flavoenzyme that participates in photosynthesis in the transfer of electrons from PS I, through Ferredoxin (Fd), to NADP+. The reaction involves the formation of a transient complex between the FNR and Fd proteins that facilitates the pass of one electron from the iron-sulfur center in Fd to the flavin group in FNR.
The molecular basis for the formation of the complex as well as for the transfer of electrons between the two centers has been investigated in our group for several years. We use site-directed mutagenesis to generate mutants of the proteins with an altered interaction surface to study the effect of this change on the rate of electron transfer reaction is studied using rapid kinetic techniques.
Information on the docking of the two proteins has also been obtained from the crystal structure of the complex that has been obtained at high resolution. The involvement of both charged and hydrophobic residues in both proteins has been proposed.
Similar studies using the electron transfer protein Flavodoxin have failed to obtain the crystal structure of the complex as well as to find amino acid residues in the surface of Fld that could be considered essential for the complex formation as well as for the electron transfer reaction between the two proteins.
We present some new data on the studies with flavodoxin mutants that have been addressed to change the complementarity of the interface between the two proteins as well as the difference in redox potential between the two proteins that represents the driving force for the electron transfer reaction.

Nogues, I, Campos, L.A., Sancho, J., Gómez-Moreno, C., Mayhew, S.G., Medina, M. (2004) Biochemistry 43, 15111-15121

Nogues, I., Hervás, M., Peregrina, J.R., Navarro, J.A., De la Rosa, M.A., Gómez-Moreno, C. and Medina, M. (2005) Biochemistry, 44, 97-104