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PDBsum entry 2q3c
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References listed in PDB file
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Key reference
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Title
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Structural insights into catalysis and inhibition of o-Acetylserine sulfhydrylase from mycobacterium tuberculosis. Crystal structures of the enzyme alpha-Aminoacrylate intermediate and an enzyme-Inhibitor complex.
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Authors
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R.Schnell,
W.Oehlmann,
M.Singh,
G.Schneider.
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Ref.
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J Biol Chem, 2007,
282,
23473-23481.
[DOI no: ]
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PubMed id
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Abstract
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Cysteine biosynthetic genes are up-regulated in the persistent phase of
Mycobacterium tuberculosis, and the corresponding enzymes are therefore of
interest as potential targets for novel antibacterial agents. cysK1 is one of
these genes and has been annotated as coding for an O-acetylserine
sulfhydrylase. Recombinant CysK1 is a pyridoxal phosphate (PLP)-dependent enzyme
that catalyzes the conversion of O-acetylserine to cysteine. The crystal
structure of the enzyme was determined to 1.8A resolution. CysK1 belongs to the
family of fold type II PLP enzymes and is similar in structure to other
O-acetylserine sulfhydrylases. We were able to trap the alpha-aminoacrylate
reaction intermediate and determine its structure by cryocrystallography.
Formation of the aminoacrylate complex is accompanied by a domain rotation
resulting in active site closure. The aminoacrylate moiety is bound in the
active site via the covalent linkage to the PLP cofactor and by hydrogen bonds
of its carboxyl group to several enzyme residues. The catalytic lysine residue
is positioned such that it can protonate the Calpha-carbon atom of the
aminoacrylate only from the si-face, resulting in the formation of L-cysteine.
CysK1 is competitively inhibited by a four-residue peptide derived from the
C-terminal of serine acetyl transferase. The crystallographic analysis reveals
that the peptide binds to the enzyme active site, suggesting that CysK1 forms an
bi-enzyme complex with serine acetyl transferase, in a similar manner to other
bacterial and plant O-acetylserine sulfhydrylases. The structure of the
enzyme-peptide complex provides a framework for the design of strong binding
inhibitors.
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Figure 3.
FIGURE 3. Structure of the complex of CysK1 with  -aminoacrylate. A,
superposition of holo-CysK1 (blue) and the CysK1-aminoacrylate
complex (red) illustrating the conformational changes of the
N-terminal domain leading to the closure of the active site. The
covalent intermediate forming the external Schiff base with PLP
is shown as a stick model (yellow). B, part of the 2F[o] - F[o]
electron density map, contoured at 1.2  , showing formation of
the -aminoacrylate
intermediate. C, schematic showing the interactions of the
reaction intermediate with enzyme residues in the active site.
Hydrogen bonds are indicated by dashed lines. D, stereo view of
the active site of the CysK1- -aminoacrylate
intermediate complex. The red spheres indicate the positions of
bound water molecules.
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Figure 6.
FIGURE 6. Structure of the CysK1-peptide complex. A, stereo
view of the active site of CysK1 with the bound DFSI peptide,
shown in green. CysK1 amino acid residues are shown in yellow,
and water molecules are shown as red spheres. B, part of the
2F[o] - F[o] electron density map at the peptide binding site in
CysK1, contoured at 1.4 .
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2007,
282,
23473-23481)
copyright 2007.
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