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PMID:17029414

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Citation

Konas, DW, Takaya, N, Sharma, M and Stuehr, DJ (2006) Role of Asp1393 in catalysis, flavin reduction, NADP(H) binding, FAD thermodynamics, and regulation of the nNOS flavoprotein. Biochemistry 45:12596-609

Abstract

Nitric oxide synthases (NOS) are flavoheme enzymes with important roles in biology. The reductase domain of neuronal NOS (nNOSr) contains a widely conserved acidic residue (Asp(1393)) that is thought to facilitate hydride transfer between NADPH and FAD. Previously we found that the D1393V and D1393N mutations lowered the NO synthesis activity and the rates of heme and flavin reduction in full-length nNOS. To examine the mechanisms for these results in greater detail, we incorporated D1393V and D1393N substitutions into nNOSr along with a truncated NADPH-FAD domain construct (FNR) and characterized the mutants. D1393V nNOSr had markedly lower (<or=1000x) cytochrome c reductase, ferricyanide reductase, and NADPH oxidase activities than the wild type. D1393N nNOSr also had lower reductase activities (<or=10x) but had greater NADPH oxidase activity than that of the wild type, as did its FNR fragment. Both mutants had an altered interaction between FAD and the nicotinamide ring of NADP(+), slower flavin reduction by NADPH, altered FAD midpoint potentials, a normal CaM response, and, in one case (D1393N), faster flavin oxidation by O(2) and a lack of FMN shielding in response to NADPH binding. The results suggest that the two mutants have compromised catalysis for two different reasons. In D1393V nNOSr, hydride transfer from NADPH to FAD is so slow that it compromises all downstream electron-transfer events. In D1393N nNOSr, the increased oxidation of reduced flavins by O(2) and thermodynamic destabilization of the FAD semiquinone uncouples or limits electron transfer to an extent that it inhibits downstream catalysis. These effects are due in part to the mutations eliminating (D1393V) or altering (D1393N) the native side-chain hydrogen-bonding properties of Asp(1393) as well as removing its negative charge.

Links

PubMed Online version:10.1021/bi061011t

Keywords

Amino Acid Substitution; Animals; Aspartic Acid/chemistry; Base Sequence; Catalytic Domain/genetics; DNA Primers/genetics; Electron Transport; Flavin-Adenine Dinucleotide/metabolism; Hydrogen Bonding; Kinetics; Mutagenesis, Site-Directed; NADP/metabolism; Nitric Oxide Synthase Type I/chemistry; Nitric Oxide Synthase Type I/genetics; Nitric Oxide Synthase Type I/metabolism; Oxidation-Reduction; Rats; Recombinant Proteins/chemistry; Recombinant Proteins/genetics; Recombinant Proteins/metabolism; Thermodynamics

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

HUMAN:NOS1

enables

GO:0034618: arginine binding

ECO:0000304: author statement supported by traceable reference used in manual assertion

F

Seeded From UniProt

complete

RAT:NOS1

enables

GO:0004517: nitric-oxide synthase activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

RAT:NOS1

enables

GO:0010181: FMN binding

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

RAT:NOS1

enables

GO:0046870: cadmium ion binding

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

RAT:NOS1

enables

GO:0050660: flavin adenine dinucleotide binding

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

RAT:NOS1

enables

GO:0050661: NADP binding

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete


See also

References

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