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PDBsum entry 3b6h
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References listed in PDB file
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Key reference
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Title
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Structures of prostacyclin synthase and its complexes with substrate analog and inhibitor reveal a ligand-Specific heme conformation change.
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Authors
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Y.C.Li,
C.W.Chiang,
H.C.Yeh,
P.Y.Hsu,
F.G.Whitby,
L.H.Wang,
N.L.Chan.
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Ref.
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J Biol Chem, 2008,
283,
2917-2926.
[DOI no: ]
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PubMed id
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Abstract
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Prostacyclin synthase (PGIS) is a cytochrome P450 (P450) enzyme that catalyzes
production of prostacyclin from prostaglandin H(2). PGIS is unusual in that it
catalyzes an isomerization rather than a monooxygenation, which is typical of
P450 enzymes. To understand the structural basis for prostacyclin biosynthesis
in greater detail, we have determined the crystal structures of ligand-free,
inhibitor (minoxidil)-bound and substrate analog U51605-bound PGIS. These
structures demonstrate a stereo-specific substrate binding and suggest features
of the enzyme that facilitate isomerization. Unlike most microsomal P450s, where
large substrate-induced conformational changes take place at the distal side of
the heme, conformational changes in PGIS are observed at the proximal side and
in the heme itself. The conserved and extensive heme propionate-protein
interactions seen in all other P450s, which are largely absent in the
ligand-free PGIS, are recovered upon U51605 binding accompanied by water
exclusion from the active site. In contrast, when minoxidil binds, the
propionate-protein interactions are not recovered and water molecules are
largely retained. These findings suggest that PGIS represents a divergent
evolution of the P450 family, in which a heme barrier has evolved to ensure
strict binding specificity for prostaglandin H(2), leading to a radical-mediated
isomerization with high product fidelity. The U51605-bound structure also
provides a view of the substrate entrance and product exit channels.
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Figure 1.
FIGURE 1. Proposed mechanism for PGI[2] biosynthesis. A,
chemical structures of substrate PGH[2], substrate analog
U51605, and inhibitor minoxidil. B, a proposed mechanism for the
reaction catalyzed by PGIS (R1, CH[2]-(CH[2])[2]-COOH; R2,
CH-CHOH-(CH[2])[4]-CH[3]) (6).
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Figure 5.
FIGURE 5. The minoxidil-bound hPGIS. A, a F[o] - F[c] omit
map contoured at 2.7  shows unbiased electron
density for minoxidil. B, structural changes around the active
site, Cys ligand loop, and B' helix upon minoxidil binding. The
ligand-free (blue) and minoxidil-bound (gold) structures were
superimposed over all equivalent C  atom pairs. The
minoxidil-induced stacking between Phe^96 and His^438 is
indicated by the dashed lines.
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The above figures are
reprinted
from an Open Access publication published by the ASBMB:
J Biol Chem
(2008,
283,
2917-2926)
copyright 2008.
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