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PDBsum entry 2a1h
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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 determinants for branched-Chain aminotransferase isozyme-Specific inhibition by the anticonvulsant drug gabapentin.
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Authors
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M.Goto,
I.Miyahara,
K.Hirotsu,
M.Conway,
N.Yennawar,
M.M.Islam,
S.M.Hutson.
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Ref.
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J Biol Chem, 2005,
280,
37246-37256.
[DOI no: ]
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PubMed id
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Abstract
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This study presents the first three-dimensional structures of human cytosolic
branched-chain aminotransferase (hBCATc) isozyme complexed with the neuroactive
drug gabapentin, the hBCATc Michaelis complex with the substrate analog,
4-methylvalerate, and the mitochondrial isozyme (hBCATm) complexed with
gabapentin. The branched-chain aminotransferases (BCAT) reversibly catalyze
transamination of the essential branched-chain amino acids (leucine, isoleucine,
valine) to alpha-ketoglutarate to form the respective branched-chain alpha-keto
acids and glutamate. The cytosolic isozyme is the predominant BCAT found in the
nervous system, and only hBCATc is inhibited by gabapentin. Pre-steady state
kinetics show that 1.3 mm gabapentin can completely inhibit the binding of
leucine to reduced hBCATc, whereas 65.4 mm gabapentin is required to inhibit
leucine binding to hBCATm. Structural analysis shows that the bulky gabapentin
is enclosed in the active-site cavity by the shift of a flexible loop that
enlarges the active-site cavity. The specificity of gabapentin for the cytosolic
isozyme is ascribed at least in part to the location of the interdomain loop and
the relative orientation between the small and large domain which is different
from these relationships in the mitochondrial isozyme. Both isozymes contain a
CXXC center and form a disulfide bond under oxidizing conditions. The structure
of reduced hBCATc was obtained by soaking the oxidized hBCATc crystals with
dithiothreitol. The close similarity in active-site structures between cytosolic
enzyme complexes in the oxidized and reduced states is consistent with the small
effect of oxidation on pre-steady state kinetics of the hBCATc first
half-reaction. However, these kinetic data do not explain the inactivation of
hBCATm by oxidation of the CXXC center. The structural data suggest that there
is a larger effect of oxidation on the interdomain loop and residues surrounding
the CXXC center in hBCATm than in hBCATc.
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Figure 4.
FIGURE 4. Schematic diagram showing hydrogen-bond and
salt-bridge interactions of the active-site residues. Putative
interactions are shown by dotted lines if the acceptor and donor
are less than 3.5 Å apart. The hydrogen bonds associated
with the phosphate group of PLP are omitted for clarity. A,
hBCATc-ox complexed with gabapentin. B, hBCATc-ox complexed with
4MeVA.
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Figure 6.
FIGURE 6. Stereo diagram of the superimposed active sites
of hBCATc-ox·gabapentin and hBCATc·gabapentin. The
residues and gabapentin, which represent
hBCATc-ox·gabapentin and hBCATc·gabapentin, are
shown in brown and deep blue, respectively.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2005,
280,
37246-37256)
copyright 2005.
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