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PDBsum entry 1asl
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Aminotransferase
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PDB id
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1asl
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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 structures of escherichia coli aspartate aminotransferase in two conformations. Comparison of an unliganded open and two liganded closed forms.
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Authors
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J.Jäger,
M.Moser,
U.Sauder,
J.N.Jansonius.
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Ref.
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J Mol Biol, 1994,
239,
285-305.
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PubMed id
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Note In the PDB file this reference is
annotated as "TO BE PUBLISHED".
The citation details given above were identified by an automated
search of PubMed on title and author
names, giving a
perfect match.
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Abstract
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Three crystal structures of wild type E. coli aspartate aminotransferase
(E.C.2.6.1.1) in space group P2(1) have been determined at resolution limits
between 2.6 and 2.35 A. The unliganded enzyme and its complexes with the
substrate analogues maleate and 2-methylaspartate resulted in different
conformations. The unit cell parameters of the unliganded and the inhibited
enzyme are a = 87.2, b = 79.9, c = 89.8 A and beta = 119.1 degrees, and a =
85.4, b = 79.8, c = 89.5 A and beta = 118.6 degrees, respectively. The
crystallographic symmetry is pseudo-C222(1). The liganded enzyme structures were
solved by difference Fourier techniques from that of a Val39-->Leu mutant
partially refined to an R-factor of 0.22 at 2.85 A. They have a "closed"
conformation like the chicken mAATase:maleate complex. The models were refined
to R-factors of 0.19 (maleate complex) and 0.18 (2-methylaspartate complex) by
molecular dynamics and restrained least squares methods. The unliganded crystal
form was solved by molecular replacement and refined to an R-factor of 0.19 at
2.5 A resolution. The structure is in a "half-open" conformation, with the small
domain rotated about 6 degrees from the closed conformation. The cofactor
pyridoxal phosphate has a more relaxed conformation than in mAATase. Both
maleate and 2-methylaspartate are hydrogen-bonded to the active site as in
mAATase. The C alpha-CH3 bond of 2-methylaspartate is oriented at right angles
to the cofactor pyridine ring, the most productive orientation for
alpha-deprotonation of the substrate L-aspartate. Comparisons with earlier
determined eAATase structures in space group C222(1) revealed differences that
can probably be attributed to the somewhat lower resolution of the orthorhombic
structures and/or mutations in the eAATases used in those studies. The present
P2(1) structures confirm the justification of extrapolating properties of active
site point mutants to the vertebrate isozymes. They will serve as reference in
the interpretation of the properties of further site-directed mutants in
continued studies of structure-function relationships of this enzyme.
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