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

Abstract

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 Å. This structure reveals differences in the mobility of specific 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 affecting the entrance of nicotinamide into the active site. This structure opens the possibility of rationally designing drugs against the X. axonopodis pv. citri phytopathogen.

Figure 1

(a) Cartoon representation of XacFPR structure. The N-domain is shown in yellow and the C-domain in green. The unbiased (before inclusion of FAD) |F _o | − | F _c | , F _calc electron density map is shown at 2.2 σ. FAD is in sticks with carbons in grey. Chloride ion is a red sphere. (b) Stereo representation of the FAD environment. Carbon atoms of amino acid residues and FAD are shown in white and orange, respectively. H-bonds involved in FAD stabilization are represented as dotted lines. (c) Cartoon superimposition of the active site of XacFPR (in grey), PaFPR:NADP⁺ complex (pdb 3crz, in orange), and RcFPR:NADP⁺ complex (pdb 2vnj, in green). FAD, in sticks and with carbons in grey, belongs to XacFPR structure and occupies similar position to FADs of Pa and RcFPRs complexes. NADP⁺s from complexes are in sticks. C-terminuses of the three structures are pointed to by arrows.

Figure 2

(a) Stereo cartoon representation of the α-carbon B-factors alignment for XacFPR (green), AvFPR (pink), PaFPR (blue) and RcFPR (yellow) by Pymol. Positions with larger fluctuations are indicated in wide cartoon while those with the lower fluctuations are shown as thin cartoon. FAD from XacFPR is displayed in space filling with carbons in green. Inset; detail of C-terminal homologous residues of FPRs from subclass IA in sticks. Interactions between Glu258 and FAD in XacFPR are shown as dashed lines. The FAD and the side-chain of Glu258 are in space filling and sticks, respectively, and both CPK coloured. (b) Detail of the different exposition of FAD in XacFPR (blue) and RcFPR (dark yellow) due to the conformation of side chains of Lys259 and Glu270, respectively. Red balls represent water molecules and respective polar contacts of Lys259 and Glu270 with their environment are shown in dashed lines.