PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

Role of Anabaena flavodoxin hydrophobic residues in protein-protein interaction and electron transfer to ferredoxin-NADP⁺ reductase. Susana Frago^*,1, Guillermina Goñi¹, Ana Serrano¹, Stephen Mayhew², Carlos Gomez-Moreno¹, Milagros Medina¹, ¹ Departamento de Bioquímica y Biología Molecular y Celular, Zaragoza, Spain² Departamento de Bioquímica y Biología Molecular y Celular, Zaragoza, Spain

ABSTRACT- Biochemical and structural studies indicate that electrostatic and hydrophobic interactions play an important role in the formation of optimal complexes for efficient electron transfer between Ferredoxin-NADP⁺ reductase (FNR) and ferredoxin (Fd). Moreover, it has been shown that several charged and hydrophobic residues on the FNR surface are also critical for the interaction with flavodoxin (Fld), although, so far, no key residue on the Fld surface has been found to be the counterpart of such FNR side-chains. In the present study, side-chains with a hydrophobic character on the Anabaena Fld surface have been modified, either by the introduction of charged side-chains or by its elimination. Our results indicate that although Trp57, Ile59 and Ile92 contribute to the orientation and optimisation of the Fld interaction with FNR, none of these side-chains is individually involved in the formation of crucial interactions for optimal orientation with FNR. These data also support the idea that the FNR/Fld interaction is less specific than the FNR/Fd one. Additionally, we will show that these residues, situated in the close environment of the FMN isoalloxazine ring, modulate the flavin redox properties within the protein environment. In conclusion, our data indicate that these residues modulate the redox properties of Fld as well as its abilities to bind and to exchange electrons with FNR.

KEY WORDS: protein-protein interaction, reduction potential, electron transport, flavoproteins