Crystal structure of FAD-containing ferredoxin-NADP+ reductase from Xanthomonas axonopodis pv. citri

TONDO, M. L.; HURTADO GUERRERO, R; SÁNCHEZ-AZQUETA, A; CECCARELLI, E. A.; MEDINA, M; ORELLANO, E. G.; MARTÍNEZ-JÚLVEZ, M

Sevilla

Congreso; Congreso; 22nd IUBMB-37th FEBS Congress. From Single Molecules to Systems Biology.; 2012; 2012

IUBMB FEBS

Ferredoxin-NADP(H) reductases (FNRs, EC 1.18.1.2) constitute a family of hydrophilic, FAD-containing monomeric enzymes that deliver NADPH or low potential one-electron donors to redox-based metabolisms in plastids, mitochondria and bacteria. In heterotrophic bacteria, the FNR activity provides reduced ferredoxin and flavodoxin to diverse reactions. Based on phylogenetic analysis the prokaryotes FNR variants (collectively known as FPRs) have been classified into subclasses I and II represented by the Azotobacter vinelandii and the Escherichia coli, respectively, FPR prototypes. Structures of bacterial and plastidic FNRs contain two distinct domains; the C-terminal domain that has a binding site for NADP(H) and the N-terminal region that binds the cofactor FAD. In bacterial enzymes, the FAD is in a bent conformation that could be the explanation for the very low turnover rates for NADPH oxidation exhibited in the diaphorase activity of the bacterial FPRs with respect to those of plastidic enzymes. Additionally, a subdivision of subclass I bacterial FNRs, IA and IB, was proposed based on differences of their carboxy-terminal primary sequences. To better understand the structural and functional divergence between subclass I FPRs, in the present work we have determined the crystal structure of XacFPR to a resolution of 1.5 Å. This FPR comes from the parasite Xanthomonas axopodis pv. citri, a Gram-negative bacterium responsible for citrus canker, a severe disease that affects most commercial citrus cultivars. The final structure reveals that XacFPR adopts many structural characteristics of the bacterial subclass IA, although some structural differences among FPRs from subclass IA and IB have been detected. The ones centered at the FAD environment and at the NADP+ binding site could help to better understand the kinetic behaviour of these oxidoreductases. Furthermore this enzyme represents a potential target to treat infections caused by  axonopodis pv. citri. The information obtained may provide a rationale to develop new inhibitors of these enzymes.