flavin-adenine-dinucleotide and adenosine-2--5--diphosphate

The three-dimensional structure of spinach ferredoxin-NADP+ reductase (NADP+, nicotinamide adenine dinucleotide phosphate) has been determined by x-ray diffraction at 2.6 angstroms (A) resolution and initially refined to an R factor of 0.226 at 2.2 A resolution. The model includes the flavin-adenine dinucleotide (FAD) prosthetic group and the protein chain from residue 19 through the carboxyl terminus at residue 314 and is composed of two domains. The FAD binding domain (residues 19 to 161) has an antiparallel beta barrel core and a single alpha helix for binding the pyrophosphate of FAD. The NADP binding domain (residues 162 to 314) has a central five-strand parallel beta sheet and six surrounding helices. Binding of the competitive inhibitor 2'-phospho-AMP (AMP, adenosine monophosphate) places the NADP binding site at the carboxyl-terminal edge of the sheet in a manner similar to the nucleotide binding of the dehydrogenase family. The structures reveal the key residues that function in cofactor binding and the catalytic center. With these key residues as a guide, conclusive evidence is presented that the ferredoxin reductase structure is a prototype for the nicotinamide dinucleotide and FAD binding domains of the enzymes NADPH-cytochrome P450 reductase, NADPH-sulfite reductase, NADH-cytochrome b5 reductase, and NADH-nitrate reductase. Thus this structure provides a structural framework for the NADH- or NADPH-dependent flavoenzyme parts of five distinct enzymes involved in photosynthesis, in the assimilation of inorganic nitrogen and sulfur, in fatty-acid oxidation, in the reduction of methemoglobin, and in the metabolism of many pesticides, drugs, and carcinogens.

Topics: Adenosine Diphosphate; Amino Acid Sequence; Binding Sites; Crystallization; Ferredoxin-NADP Reductase; Ferredoxins; Flavin-Adenine Dinucleotide; Hydrogen Bonding; Molecular Sequence Data; Molecular Structure; NADP; Nucleotides; Plants; Protein Conformation; Sequence Homology, Nucleic Acid; X-Ray Diffraction

The interaction between 2',5'-ADP and NADPH-adrenodoxin reductase from bovine adrenocortical mitochondria was examined by titrating the enzyme with 2',5'-ADP, while the 31P-signals of 2',5'-ADP were being monitored by 31P-NMR. From the titration profile, the dissociation constant for the complex of the enzyme with 2',5'-ADP was estimated to be 0.22 +/- 0.05 mM. Adrenodoxin reductase was reconstituted with 13C-enriched FADs. The 13C-enriched FADs used were [2-13C]-, [4,10 alpha-13C2]-, and [4 alpha-13C]FAD. The 13C-NMR spectra of these reconstituted enzyme preparations showed 13C-resonance peaks corresponding to the enriched carbon atoms at 160.6 , 165.1, 136.6, and 152.4 ppm (2-, 4-, 4 alpha-, and 10 alpha-13C atoms, respectively). When 2',5'-ADP was bound to the reconstituted enzyme, these 13C-resonance peaks did not shift appreciably from those of the unbound enzyme, whereas in the complex of the reconstituted enzyme with NADP+, the signals for 4- and 10 alpha-13C shifted to higher fields by 2.1 and 0.7 ppm, respectively and the 4 alpha-13C signal shifted to a lower field by 1.4 ppm. These results suggest that in the complex of the enzyme with NADP+ the pyridine moiety is located in the vicinity of C(4 alpha)-C(4) region and that the pi-electron density of the 4 alpha-position of flavin is decreased in the enzyme-NADP+ complex. This argues in favor of the electron transfer from the dihydropyridine moiety of NADPH to the electron-deficient N(5) = C(4 alpha) region of flavin.

Topics: Adenosine Diphosphate; Adrenal Cortex; Animals; Binding Sites; Cattle; Ferredoxin-NADP Reductase; Flavin-Adenine Dinucleotide; In Vitro Techniques; Magnetic Resonance Spectroscopy; Molecular Probes