Hindawi Publishing Corporation BioMed Research International Volume 2013, Article ID 906572, 6 pages http://dx.doi.org/10.1155/2013/906572 Research Article Crystal Structure of the FAD-Containing Ferredoxin-NADP + Reductase from the Plant Pathogen Xanthomonas axonopodis pv. citri María Laura Tondo, 1 Ramon Hurtado-Guerrero, 2,3 Eduardo A. Ceccarelli, 1 Milagros Medina, 3,4 Elena G. Orellano, 1 and Marta Martínez-Júlvez 3,4 1 Molecular Biology Division, Instituto de Biolog´ ıa Molecular y Celular de Rosario (IBR), CONICET, Facultad de Ciencias Bioqu´ ımicas y Farmac´ euticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina 2 Fundaci´ on ARAID, Ediicio Pignatelli 36, 50004 Zaragoza, Spain 3 Institute of Biocomputation and Physics of Complex Systems (BIFI), Joint Unit BIFI-Rocasolano, Universidad de Zaragoza, 50018 Zaragoza, Spain 4 Departamento de Bioqu´ ımica y Biolog´ ıa Molecular y Celular, Facultad de Ciencias, Pedro Cerbuna 12, Universidad de Zaragoza, 50009 Zaragoza, Spain Correspondence should be addressed to Marta Mart´ ınez-J´ ulvez; mmartine@unizar.es Received 2 May 2013; Accepted 7 July 2013 Academic Editor: Stefan Knapp Copyright © 2013 Mar´ ıa Laura Tondo et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We have solved the structure of ferredoxin-NADP(H) reductase, FPR, from the plant pathogen Xanthomonas axonopodis pv. citri, responsible for citrus canker, at a resolution of 1.5 ˚ A. his structure reveals diferences in the mobility of speciic loops when compared to other FPRs, probably unrelated to the hydride transfer process, which contributes to explaining the structural and functional divergence between the subclass I FPRs. Interactions of the C-terminus of the enzyme with the phosphoadenosine of the cofactor FAD limit its mobility, thus afecting the entrance of nicotinamide into the active site. his structure opens the possibility of rationally designing drugs against the X. axonopodis pv. citri phytopathogen. 1. Introduction Ferredoxin-NADP(H) reductases (FNRs, EC 1.18.1.2) con- stitute a family of hydrophilic FAD-containing monomeric enzymes that deliver NADPH or low potential one-electron donors to redox-based metabolisms in plastids, mitochon- dria, and bacteria [1]. In heterotrophic bacteria, this activity provides reduced ferredoxin and lavodoxin to diverse reac- tions involved in amino acid and nucleotide metabolisms, biotin synthesis, and iron-sulphur cluster assembly, as well as for the nitrogenase complex [1]. Based on phylogenetic analysis, the FNR forms present in most prokaryotes (collec- tively known as FPRs) have been classiied into two subclasses represented by the Azotobacter vinelandii (subclass I) and the Escherichia coli (subclass II) FPR prototypes [1]. Structures of bacterial FPRs, as well as those of plastidic FNRs, are folded in two distinct domains: the C-terminus with a binding site for NADP(H) and the N-terminus binding the cofactor FAD. Unlike plastidic enzymes, bacterial ones show a bent conformation of FAD. his conformation is stabilised by an intramolecular H-bond between the N6 atom of the adeno- sine and the N1 atom of the isoalloxazine rings, and by stacking of an aromatic side chain against the carboxy- terminal extension and the adenosine moiety. he very low turnover rates for the oxidation of NADPH exhibited by bacterial FPRs in comparison with plastidic enzymes may be associated with this FAD folded conformation, unlike the extended conformation in plastidic FNRs [2] (see Table S1 in Supplementry Material available online http://dx.doi.org/ 10.1155/2013/906572). Xanthomonas axonopodis pv. citri is a gram-negative bacterium responsible for citrus canker, a severe disease that