@article{Wang07, author={An Wang and Yuhong Zeng and Huijong Han and Saroja Weeratunga and Bailey N. Morgan and Pierre Mo{\"e}nne-Loccoz and Ernst Sch{\"o}nbrunn and Mario Rivera}, title={Biochemical and Structural Characterization of \textit{Pseudomonas aeruginosa} {Bfd} and {FPR}: Ferredoxin {NADP}$^+$ Reductase and not Ferredoxin is the Redox Partrner of Heme Oxygenase under Iron-Starvation Conditions}, journal={Biochemistry}, volume={46}, pages={12198--12211}, year={2007}, keywords={KU; FPR;}, url={https://doi.org/10.1021/bi7013135}, doi={10.1021/bi7013135}, abstract={Among the 118 genes upregulated by \emph{Pseudomonas aeruginosa} in response to iron starvation [Ochsner, U. A., Wilderman, P. J., Vasil, A. I., and Vasil, M. L. (2002) \textit{Mol. Microbiol.} \textbf{45}, 1277-1287], we focused on the products of the two genes encoding electron transfer proteins, as a means of identifying the redox partners of the heme oxygenase ($pa$-HO) expressed under low-iron stress conditions. Biochemical and spectroscopic investigations demonstrated that the \emph{bfd} gene encodes a 73-amino acid protein ($pa$-Bfd) that incorporates a [2Fe-2S]$^{2+/+}$ center, whereas the \emph{fpr} gene encodes a 258-residue NADPH-dependent ferredoxin reductase ($pa$-FPR) that utilizes FAD as a cofactor. In vitro reconstitution of $pa$-HO catalytic activity with the newly characterized proteins led to the surprising observation that $pa$-FPR efficiently supports the catalytic cycle of $pa$-HO, without the need of a ferredoxin. In comparison, electron transfer from $pa$-Bfd to $pa$-HO is sluggish, which strongly argues against the possibility that the seven electrons needed by $pa$-HO to degrade biliverdin are transferred from NADPH to $pa$-HO in a ferredoxin (\emph{Bfd})-dependent manner. Given that $pa$-HO functions to release iron from exogenous heme acquired under iron-starvation conditions, the use of a flavoenzyme rather than an iron-sulfur center-containing protein to support heme degradation is an efficient use of resources in the cell. The crystal structure of $pa$-FPR (1.6 $\AA$ resolution) showed that its fold is comparable that of the superfamily of ferredoxin reductases and most similar to the structure of \emph{Azotobacter vinelandii} FPR and \emph{Escherichia coli} flavodoxin reductase. The latter two enzymes interact with distinct redox partners, a ferredoxin and a flavodoxin, respectively. Hence, findings reported herein extend the range of redox partners recognized by the fold of $pa$-FPR to include a heme oxygenase ($pa$-HO).}
}
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doi:10.1021/bi7013135