IBR   13079
INSTITUTO DE BIOLOGIA MOLECULAR Y CELULAR DE ROSARIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The structural traits for the high catalytic efficiency of ferredoxin-NADP+ reductases
Autor/es:
CECCARELLI, E. A.; CATALANO DUPUY, D. L.; MUSUMECI, M. A.; TONDO, M. L.; ORELLANO, E. G.
Lugar:
Berkeley
Reunión:
Simposio; 17th International Symposium on Flavins and Flavoproteins; 2011
Institución organizadora:
Universidad de Berkeley
Resumen:
Simposio por invitacion a E. A. Ceccarelli Ferredoxin-NADP+ reductases (FNRs, EC 1.18.1.2) constitute a family of hydrophilic, monomeric enzymes that contain non-covalently bound FAD as prosthetic group. These flavoenzymes deliver NADPH or low potential one-electron donors (ferredoxin, flavodoxin, heme-oxigenase) to redox-based metabolisms in plastids, mitochondria and bacteria. Plant type FNRs can be divided in two classes: plastidic, characterized by an extended FAD conformation and high catalytic turnover rates for the diaphorase reaction using NADPH as substrate, and a second class of bacterial proteins displaying a bent conformation of FAD and low turnover rates for the same reaction. Both enzyme families have adapted their catalytic capacities likely to meet the metabolic needs of the processes in which they are involved. The plastidic FNRs need to fulfill the production of high amounts of reducing power during photosynthesis. In contrast, bacterial FNRs act on the homeostasis of the NADP(H) pool or provide electrons from NADPH through flavodoxin or ferredoxin to metabolic pathways that proceed at a much lower pace. We have searched for the structural backgrounds that tailor the catalytic competence of these enzymes. We have obtained several conclusions from our studies: 1) the mobility of the carboxyl-terminal backbone, mainly the terminal tyrosine, is essential for obtaining highly efficient plastidic FNRs; 2) the main role of the terminal tyrosine in these enzymes is to destabilize the interaction of the nicotinamide with the FAD. In the absence of the tyrosine, this role can be carried out by aromatic compounds which can freely diffuse in solution and establish a dynamic equilibrium with the NADP(H) nicotinamide; 3) the interaction of the tyrosine and the prosthetic group FAD is precisely regulated by adjusting the volume of the amino acids surrounding the catalytic site; 4) the structure of plastidic enzymes locates the FAD in an open optimal position optimizing the flavin conformation and the substrate access to the catalytic site; 5) the structure of the carboxy-terminal region in the bacterial enzymes appears to be the main determinant of low catalytic efficiency. Although bacterial and plastidic FNRs display highly conserved overall architecture, subtle structural changes that influence the access of the NADP(H) to the catalytic site greatly impact on the catalytic behaviour of these enzymes. In bacterial FNRs the carboxy-terminal region may provide an extra regulation to their catalytic competence and allow for the modulation of the specificity of the interaction with their redox partners.