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PDBsum entry 1f20
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Oxidoreductase
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PDB id
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1f20
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Crystal structure of the FAD/NADPH-Binding domain of rat neuronal nitric-Oxide synthase. Comparisons with NADPH-Cytochrome p450 oxidoreductase.
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Authors
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J.Zhang,
P.Martàsek,
R.Paschke,
T.Shea,
B.S.Siler masters,
J.J.Kim.
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Ref.
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J Biol Chem, 2001,
276,
37506-37513.
[DOI no: ]
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PubMed id
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Abstract
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Nitric-oxide synthase (NOS) is composed of a C-terminal, flavin-containing
reductase domain and an N-terminal, heme-containing oxidase domain. The
reductase domain, similar to NADPH-cytochrome P450 reductase, can be further
divided into two different flavin-containing domains: (a) the N terminus,
FMN-containing portion, and (b) the C terminus FAD- and NADPH-binding portion.
The crystal structure of the FAD/NADPH-containing domain of rat neuronal
nitric-oxide synthase, complexed with NADP(+), has been determined at 1.9 A
resolution. The protein is fully capable of reducing ferricyanide, using NADPH
as the electron donor. The overall polypeptide fold of the domain is very
similar to that of the corresponding module of NADPH-cytochrome P450
oxidoreductase (CYPOR) and consists of three structural subdomains (from N to C
termini): (a) the connecting domain, (b) the FAD-binding domain, and (c) the
NADPH-binding domain. A comparison of the structure of the neuronal NOS
FAD/NADPH domain and CYPOR reveals the strict conservation of the flavin-binding
site, including the tightly bound water molecules, the mode of NADP(+) binding,
and the aromatic residue that lies at the re-face of the flavin ring, strongly
suggesting that the hydride transfer mechanisms in the two enzymes are very
similar. In contrast, the putative FMN domain-binding surface of the NOS protein
is less positively charged than that of its CYPOR counterpart, indicating a
different nature of interactions between the two flavin domains and a different
mode of regulation in electron transfer between the two flavins involving the
autoinhibitory element and the C-terminal 33 residues, both of which are absent
in CYPOR.
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Figure 2.
Fig. 2. A stereo ribbon diagram of the nNOS-FAD/NBD
structure. From N to C termini (bottom to top): the connecting
domain is shown in red, the FAD domain is shown in green, and
the NADPH domain is shown in blue. The cofactors, NADP+ and FAD,
are shown with ball and sticks in red and yellow, respectively.
Both N and C termini are also indicated. This figure was
prepared with Molscript (34) and rendered with Raster3D (35).
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Figure 5.
Fig. 5. Residues in the vicinity of the FAD isoalloxazine
ring. The pyrimidine side of the FAD ring makes an extensive
hydrogen bonding network with the main chain atoms (carbonyl
oxygens of Thr1191 and Ala^1193 and the amide nitrogen of
Ala^1193) of the polypeptide and two tightly bound water
molecules, W1 and W2. The water molecule W2 might play a role of
general acid/base in the protonation/deprotonation of the N1
atom of the flavin that is necessary during catalysis. The
hydroxyl group of Ser1176 lies on the same plane as the FAD ring
and is 3.7 Å away from the N5 atom of FAD. It also makes
hydrogen bonds with Asp1393 and the O4 atom of the FAD ring. The
carboxylate of Asp1393 makes a hydrogen bond with His1032 and is
3.7 Å away from the sulfhydryl group of Cys1349. Hydrogen
bonds are indicated by thick dashed lines, and distances between
3.3 and 3.7 Å are indicated by thin dashed lines. The
color scheme used is as follows: oxygen, dark gray; nitrogen,
medium gray; and carbon, light gray.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2001,
276,
37506-37513)
copyright 2001.
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