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.