IBR   13079
INSTITUTO DE BIOLOGIA MOLECULAR Y CELULAR DE ROSARIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Structural Characterization of the Ferredoxin-NADP(H) Reductase and Flavodoxin NifF system from Rhodobacter capsulatus by X-ray crystallography.
Autor/es:
INMACULADA PEREZ-DORADO; ANA BORTOLOTTI; NÉSTOR CORTEZ; JUAN. A HERMOSO
Lugar:
Jaca, Spain
Reunión:
Simposio; 16th Symposiumon Flavins and Flavoproteins; 2008
Resumen:
FPR from Rhodobacter capsulatus is a bacterial ferredoxin NADP(H) reductase which has been proponed to act as electrón shuttle between the NADP(H) pool of the cell and the flavodoxin NifF, a potencial electrón carrier to the nitrogenase [1,2]. Interaction and electron transfer processes of the FPR with NADP(H) and NifF take place with turnover values which are significantly lower than those exhibited by plant and cyanobacterial FNRs (or plastídica FNRs) [2,3]. In order to elucidate the structural features responsible of the lower efficiency of this enzyme, we have crystallized and determined the three-dimensional structure of the FPR in native conditions at 1.7 Å resolution and in complex with NADP+ and 2´P-AMP at a resolution between 2.4-1.9 Å [3,4,5]. Native FPR and coenzyme complexes show clear differences around the coenzyme binding site. The most relevant ones concern the bent conformation of the FAD, the extension of six amino-acids at the C-terminal, the lack of the re-face tyrosine highly conserved in FNR enzymes and differences in the amino-acid composition of the adenosine binding site. These differences points to the existence of a different mechanism in coenzyme binding and in the regulation of the nicotinamide entrance within the active site [5]. On the other hand, complex formation between the FPR and NifF seems to be the limiting step in the catalytic cycle of the reductase [3]. Efforts in the characterization of the interactions between the two flavoproteins have been performed and, in this sense, we have solved the crystallographic structure of NifF at 2.2 Å resolution [6]. Analysis of NifF structure reveals the existence of remarkable differences in the electrostatic potential surface respect other flavodoxins. NifF presents a basic patch near its prosthetic group which alters the dipole moment orientation of the protein respect its homologues which may affect the efficiency of the complex formation.