Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: KEGG:D02011 (FAD)
 5,530 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transient absorbance measurements following laser flash photolysis have been used to measure the rate constants for electron transfer (et) from reduced Anabaena ferredoxin (Fd) to wild-type and seven site-specific charge-reversal mutants of Anabaena ferredoxin:NADP+ reductase (FNR). These mutations have been designed to probe the importance of specific positively charged amino acid residues on the surface of the FNR molecule near the exposed edge of the FAD cofactor in the protein-protein interaction during et with Fd. The mutant proteins fall into two groups: overall, the K75E, R16E, and K72E mutants are most severely impaired in et, and the K138E, R264E, K290E, and K294E mutants are impaired to a lesser extent, although the degree of impairment varies with ionic strength. Binding constants for complex formation between the oxidized proteins and for the transient et complexes show that the severity of the alterations in et kinetics for the mutants correlate with decreased stabilities of the protein-protein complexes. Those mutated residues, which show the largest effects, are located in a region of the protein in which positive charge predominates, and charge reversals have large effects on the calculated local surface electrostatic potential. In contrast, K138, R264, K290, and K294 are located within or close to regions of intense negative potential, and therefore the introduction of additional negative charges have considerably smaller effects on the calculated surface potential. We attribute the relative changes in et kinetics and complex binding constants for these mutants to these characteristics of the surface charge distribution in FNR and conclude that the positively charged region of the FNR surface located in the vicinity of K75, R16, and K72 is especially important in the binding and orientation of Fd during electron transfer.
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PMID:Electrostatic forces involved in orienting Anabaena ferredoxin during binding to Anabaena ferredoxin:NADP+ reductase: site-specific mutagenesis, transient kinetic measurements, and electrostatic surface potentials. 1045 5

Reduction potential determinations of K75E, E139K and E301A ferredoxin-NADP+ reductases provide valuable information concerning the factors that contribute to tune the flavin reduction potential. Thus, while E139 is not involved in such modulation, the K75 side-chain tunes the flavin potential by creating a defined environment that modulates the FAD conformation. Finally, the E301 side-chain influences not only the flavin reduction potential, but also the electron transfer mechanism, as suggested from the values determined for the E301A mutant, where E(ox/rd) and E(sq/rd) shifted +41 and +102 mV, respectively, with regard to wild-type. Reduction potentials allowed estimation of binding energies differences of the FAD cofactor upon reduction.
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PMID:Role of critical charged residues in reduction potential modulation of ferredoxin-NADP+ reductase. 1204 73

The three-dimensional structures of K72E, K75R, K75S, K75Q, and K75E Anabaena Ferredoxin-NADP+ reductase (FNR) mutants have been solved, and particular structural details of these mutants have been used to assess the role played by residues 72 and 75 in optimal complex formation and electron transfer (ET) between FNR and its protein redox partners Ferredoxin (Fd) and Flavodoxin (Fld). Additionally, because there is no structural information available on the interaction between FNR and Fld, a model for the FNR:Fld complex has also been produced based on the previously reported crystal structures and on that of the rat Cytochrome P450 reductase (CPR), onto which FNR and Fld have been structurally aligned, and those reported for the Anabaena and maize FNR:Fd complexes. The model suggests putative electrostatic and hydrophobic interactions between residues on the FNR and Fld surfaces at the complex interface and provides an adequate orientation and distance between the FAD and FMN redox centers for efficient ET without the presence of any other molecule as electron carrier. Thus, the models now available for the FNR:Fd and FNR:Fld interactions and the structures presented here for the mutants at K72 and K75 in Anabaena FNR have been evaluated in light of previous biochemical data. These structures confirm the key participation of residue K75 and K72 in complex formation with both Fd and Fld. The drastic effect in FNR activity produced by replacement of K75 by Glu in the K75E FNR variant is explained not only by the observed changes in the charge distribution on the surface of the K75E FNR mutant, but also by the formation of a salt bridge interaction between E75 and K72 that simultaneously "neutralizes" two essential positive charged side chains for Fld/Fd recognition.
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PMID:Structural analysis of interactions for complex formation between Ferredoxin-NADP+ reductase and its protein partners. 1578 5