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PDBsum entry 1ege
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Electron transfer
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PDB id
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1ege
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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 the wild type and the glu376gly/thr255glu mutant of human medium-Chain acyl-Coa dehydrogenase: influence of the location of the catalytic base on substrate specificity.
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Authors
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H.J.Lee,
M.Wang,
R.Paschke,
A.Nandy,
S.Ghisla,
J.J.Kim.
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Ref.
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Biochemistry, 1996,
35,
12412-12420.
[DOI no: ]
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PubMed id
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Abstract
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Crystal structures of the wild type human medium-chain acyl-CoA dehydrogenase
(MCADH) and a double mutant in which its active center base-arrangement has been
altered to that of long chain acyl-CoA dehydrogenase (LCADH),
Glu376Gly/Thr255Glu, have been determined by X-ray crystallography at 2.75 and
2.4 A resolution, respectively. The catalytic base responsible for the
alpha-proton abstraction from the thioester substrate is Glu376 in MCADH, while
that in LCADH is Glu255 (MCADH numbering), located over 100 residues away in its
primary amino acid sequence. The structures of the mutant complexed with C8-,
C12, and C14-CoA have also been determined. The human enzyme structure is
essentially the same as that of the pig enzyme. The structure of the mutant is
unchanged upon ligand binding except for the conformations of a few side chains
in the active site cavity. The substrate with chain length longer than C12 binds
to the enzyme in multiple conformations at its omega-end. Glu255 has two
conformations, "active" and "resting" forms, with the latter apparently
stabilized by forming a hydrogen bond with Glu99. Both the direction in which
Glu255 approaches the C alpha atom of the substrate and the distance between the
Glu255 carboxylate and the C alpha atom are different from those of Glu376;
these factors are responsible for the intrinsic differences in the kinetic
properties as well as the substrate specificity. Solvent accessible space at the
"midsection" of the active site cavity, where the C alpha-C beta bond of the
thioester substrate and the isoalloxazine ring of the FAD are located, is larger
in the mutant than in the wild type enzyme, implying greater O2 accessibility in
the mutant which might account for the higher oxygen reactivity.
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