Insight into Ferredoxin-NADP(H)-reductase catalysis involving the invariant Glu in the active site

DUMIT VERÓNICA; ULLMANN MATTHIAS; CORTEZ NÉSTOR

Mar del Plata, Argentina

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigaciones Bioquímicas y Biología Molecular; 2007

SAIB Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Ferredoxin-NADP reductases are enzymes harbouring one molecule of non-covalently bound FAD. These flavoproteins (FNR/FPR) catalyse reversible reactions between obligatory one-and two-electron carriers. Even though members of the FNR/FPR superfamily (plant-type) exhibit aconserved structure, sequence analysis reveals two groups: plastidic and bacterial FNR. The first  one,characterized by an extended FAD conformation and high catalytic efficiency, is involved in photosynthesis transferring electrons to NADP+ from reduced Fd. The second one displays a folded FAD molecule and low turnover rates, and catalyses the inverse reaction, reduction of oxidized Fd fromNADPH.Analysis of protonation behaviour of FNR titrable residues was done for all crystallographic structures available up to date,as well as manyFNR-substrate complexes. To compute the protonation probabilities, Poisson-Boltzmann electrostaticcalculations and Metropolis MonteCarlo titration calculations have been performed.A highly conserved Glu in the active site showed a differential titratio behaviour in plastidic and bacterial FNRs. Thisdifference  could be related to the direction of the physiological reaction they catalyze. Also, its protonation probability proved to be sensitive tothe substrate bound, suggesting that the Glu might be involved in FNR catalytic mechanism as proton donor/acceptor.