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PDBsum entry 1fcj
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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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Identification of an allosteric anion-Binding site on o-Acetylserine sulfhydrylase: structure of the enzyme with chloride bound.
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Authors
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P.Burkhard,
C.H.Tai,
J.N.Jansonius,
P.F.Cook.
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Ref.
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J Mol Biol, 2000,
303,
279-286.
[DOI no: ]
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PubMed id
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Abstract
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A new crystal structure of O-acetylserine sulfhydrylase (OASS) has been solved
with chloride bound at an allosteric site and sulfate bound at the active site.
The bound anions result in a new "inhibited" conformation, that
differs from the "open" native or "closed" external aldimine
conformations. The allosteric site is located at the OASS dimer interface. The
new inhibited structure involves a change in the position of the "moveable
domain" (residues 87-131) to a location that differs from that in the open
or closed forms. Formation of the external aldimine with substrate is stabilized
by interaction of the alpha-carboxyl group of the substrate with a
substrate-binding loop that is part of the moveable domain. The inhibited
conformation prevents the substrate-binding loop from interacting with the
alpha-carboxyl group, and hinders formation of the external Schiff base and thus
subsequent chemistry. Chloride may be an analog of sulfide, the physiological
inhibitor. Finally, these results suggest that OASS represents a new class of
PLP-dependent enzymes that is regulated by small anions.
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Figure 2.
Figure 2. Stereo representation of the conformational
changes occurring upon sulfate and chloride binding to OASS. The
open conformation is depicted in cyan, the inhibited
conformation is depicted in magenta, the moveable domain is
shown with schematic drawings of the a-helices and b-sheets.
Binding of chloride in the allosteric site causes a peptide flip
of Pro36, which replaces the side-chain of Cys42, which then in
turn pushes the side-chain of Tyr78 to the right. This new
conformation of Tyr78 pushes Leu106 upwards and causes the
moveable domain to undergo a large conformational change into
the inhibited conformation.
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Figure 3.
Figure 3. Overlay of the open (cyan), the closed (yellow)
and the inhibited (magenta) conformations of OASS in stereo
representation. The moveable domain is shown as a cylinder
(a-helix) and arrow (b-strand) diagram. The pyridoxal
5'-phosphate (PLP) cofactor of the K41A mutant structure in
external aldimine linkage with methionine is shown in ball and
stick mode. While the C-terminal domain remains virtually
unchanged, parts of the N-terminal domain, the moveable domain,
undergo a substantial conformational change and switch from the
open conformation either to the closed conformation (external
aldimine) or to the inhibited conformation (sulfate/chloride).
The Figure was produced with the programs MOLSCRIPT [Kraulis
1991] and Raster3D [Merritt and Bacon 1997].
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2000,
303,
279-286)
copyright 2000.
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Secondary reference #1
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Title
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Ligand binding induces a large conformational change in o-Acetylserine sulfhydrylase from salmonella typhimurium.
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Authors
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P.Burkhard,
C.H.Tai,
C.M.Ristroph,
P.F.Cook,
J.N.Jansonius.
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Ref.
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J Mol Biol, 1999,
291,
941-953.
[DOI no: ]
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PubMed id
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Figure 5.
Figure 5. Overlay of a backbone trace of a monomer of the
free OASS (cyan) and the K41A mutant OASS (yellow). A portion of
the N-terminal domain is shown as a cylinder (a-helix) and arrow
(b-strand) diagram. The PLP cofactor and Asn69 (hydrogen-bonded
to O3' of the PLP) are shown in ball and stick mode. The picture
was drawn with the programs MOLSCRIPT [Kraulis 1991] and
Raster3D [Merritt and Bacon 1997].
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Figure 7.
Figure 7. Surface representation of a monomer of the OASS
dimer with PLP, Lys120, and Met119 displayed as stick models.
The native enzyme in the open conformation is shown on the right
(cyan), while the closed conformation of the K41a mutant is
shown on the left (yellow). The substrate analog methionine as
bound in the K41A mutant is shown as CPK model in both
conformations to illustrate the access to the active site PLP in
the open conformation and the nearly complete burying of the
substrate in the closed conformation. Note the small hole that
remains in the closed conformation. The picture was drawn with
the program DINO [Philippsen 1998].
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The above figures are
reproduced from the cited reference
with permission from Elsevier
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Secondary reference #2
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Title
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Three-Dimensional structure of o-Acetylserine sulfhydrylase from salmonella typhimurium.
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Authors
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P.Burkhard,
G.S.Rao,
E.Hohenester,
K.D.Schnackerz,
P.F.Cook,
J.N.Jansonius.
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Ref.
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J Mol Biol, 1998,
283,
121-133.
[DOI no: ]
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PubMed id
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Figure 2.
Figure 2. Schematic representation of the tertiary fold of
a dimer of OASS-A. The central b-sheets are colored red and the
surrounding a-helices are colored blue. In ball and stick
representation are the active site Lys41 (yellow) and the
cofactor PLP (green; the covalent link is not shown). The view
is down the non-crystallographic 2-fold axis which relates the
two subunits of the dimer. (Figure made using the program
MOLSCRIPT; [Kraulis 1991]).
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Figure 4.
Figure 4. The active-site residues of OASS-A with the
cofactor PLP covalently bound in Schiff base linkage to Lys41.
The phosphate group of the cofactor is bound at the N terminus
of helix 7 (left, first turn shown in ball and stick
representation), which interacts with the positive end of its
dipole with the negative charge of the phosphate group. Each
non-ester oxygen of the phosphate of PLP receives two hydrogen
bonds from the phosphate binding portion of the protein (Gly176
to Thr180). Four of the H-bond donors are peptide NH groups.
Helix 2 (right, first turn shown in ball and stick
representation) generates also a positive dipole moment on the
right-hand side of the cofactor and is proposed to interact with
the carboxylate group of the substrate OAS (see Figure 5). The
nitrogen N1 of PLP is hydrogen-bonded to Ser272. The cofactor
PLP is shown superimposed on an "omit map" with only PLP left
out of the structure factor calculation, contoured at 4s.
(Figure made using the program O; [Jones et al 1991]).
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The above figures are
reproduced from the cited reference
with permission from Elsevier
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