Structural prototypes for an extended family of flavoprotein reductases: Comparison of phthalate dioxygenase reductase with ferredoxin reductase and ferredoxin
Tóm tắt
The structure of phthalate dioxygenase reductase (PDR), a monomeric iron‐sulfur flavoprotein that delivers electrons from NADH to phthalate dioxygenase, is compared to ferredoxin‐NADP+ reductase (FNR) and ferredoxin, the proteins that reduce NADP+ in the final reaction of photosystem I. The folding patterns of the domains that bind flavin, NAD(P), and [2Fe‐2S] are very similar in the two systems. Alignment of the X‐ray structures of PDR and FNR substantiates the assignment of features that characterize a family of flavoprotein reductases whose members include cytochrome P‐450 reductase, sulfite and nitrate reductases, and nitric oxide synthase. Hallmarks of this subfamily of flavoproteins, here termed the FNR family, are an antiparallel
Differences in the binding sites for flavin and pyridine nucleotides determine the nucleotide specificities of FNR and PDR. The specificity of FNR for NADP+ arises primarily from substitutions in FNR that favor interactions with the 2′ phosphate of NADP+. Variations in the conformation and sequences of the loop adjoining the flavin phosphate affect the selectivity for FAD versus FMN.
The midpoint potentials for reduction of the flavin and [2Fe–2S] groups in PDR are higher than their counterparts in FNR and spinach ferredoxin, by about 120 mV and 260 mV, respectively. Comparisons of the structure of PDR with spinach FNR and with ferredoxin from
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