title: Refined crystal structure of spinach ferredoxin reductase at 1.7 A resolution: oxidized, reduced and 2'-phospho-5'-AMP bound states.
abstract: The crystal structure of spinach ferredoxin-NADP(+)-oxidoreductase (FNR), determined by multiple isomorphous replacement at 2.6 A resolution, has been refined at 1.7 A resolution to an R-factor of 17.9%. The structure of FNR bound to the competitive inhibitor 2'-phospho-5'-AMP (P-AMP) has also been refined at 1.7 A to an R-factor of 17.4% and dithionite-reduced/P-AMP-bound FNR has been refined at 2.0 A to an R-factor of 14.9%. The P-AMP-bound structure was used to construct a model for the binding of NADP+. Over 200 solvation sites were included in each structure, and many of the best defined solvation sites stabilize buried turns. A bulk solvent correction obviated the need for a low-resolution data cutoff. An acidic side-chain likely to be responsible for the low pH requirement for crystallization has been identified. Three large networks of the hydrophobic side-chains help define the FNR structure. One of these contains a large cavity far from the active site, which coincides with the lone site of sequence heterogeneity in FNR, and may provide a site for membrane attachment. The reduced structure shows that Ser96 moves toward atom N-5 of FAD and a water molecule moves toward atom N-1 of FAD, while the flavin moiety remains planar. Possible sources of a proton that must be picked up upon reduction are discussed.
authors.affiliation: Section of Biochemistry Molecular, and Cell Biology, Cornell University, Ithaca NY 14853.
authors.forename: C M
authors.initials: CM
authors.lastname: Bruns
authors.forename: P A
authors.initials: PA
authors.lastname: Karplus
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D005287:Ferredoxin-NADP Reductase / Q000737:chemistry* / Q000648:ultrastructure; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D009243:NAD / Q000737:chemistry; D010788:Photosynthesis; D010940:Plant Proteins / Q000737:chemistry / Q000648:ultrastructure; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012997:Solvents; D018724:Spinacia oleracea; D014867:Water / Q000737:chemistry
chemical_list: D010940:Plant Proteins; D012997:Solvents; D014867:Water; D009243:NAD; D005182:Flavin-Adenine Dinucleotide; D005287:Ferredoxin-NADP Reductase