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PDBsum entry 1agn
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Oxidoreductase
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PDB id
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1agn
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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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X-Ray structure of human class IV sigmasigma alcohol dehydrogenase. Structural basis for substrate specificity.
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Authors
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P.Xie,
S.H.Parsons,
D.C.Speckhard,
W.F.Bosron,
T.D.Hurley.
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Ref.
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J Biol Chem, 1997,
272,
18558-18563.
[DOI no: ]
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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
percentage match of
95%.
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Abstract
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The structural determinants of substrate recognition in the human class IV, or
sigmasigma, alcohol dehydrogenase (ADH) isoenzyme were examined through x-ray
crystallography and site-directed mutagenesis. The crystal structure of
sigmasigma ADH complexed with NAD+ and acetate was solved to 3-A resolution. The
human beta1beta1 and sigmasigma ADH isoenzymes share 69% sequence identity and
exhibit dramatically different kinetic properties. Differences in the amino
acids at positions 57, 116, 141, 309, and 317 create a different topology within
the sigmasigma substrate-binding pocket, relative to the beta1beta1 isoenzyme.
The nicotinamide ring of the NAD(H) molecule, in the sigmasigma structure,
appears to be twisted relative to its position in the beta1beta1 isoenzyme. In
conjunction with movements of Thr-48 and Phe-93, this twist widens the substrate
pocket in the vicinity of the catalytic zinc and may contribute to this
isoenzyme's high Km for small substrates. The presence of Met-57, Met-141, and
Phe-309 narrow the middle region of the sigmasigma substrate pocket and may
explain the substantially decreased Km values with increased chain length of
substrates in sigmasigma ADH. The kinetic properties of a mutant sigmasigma
enzyme (sigma309L317A) suggest that widening the middle region of the substrate
pocket increases Km by weakening the interactions between the enzyme and smaller
substrates while not affecting the binding of longer alcohols, such as hexanol
and retinol.
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Figure 1.
Fig. 1. Comparison of  ,  , and  [1] [1] dimers
by alignment of their C  atoms. All
C atoms were
used in the alignment. The^ result of the alignment using the CD
dimer of ADH is
shown. The other dimer of ADH in the
asymmetric unit gives similar results.
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Figure 2.
Fig. 2. The influence of the substitution of Ala-317  -Cys in on the
conformation of the nicotinamide ring of NAD^+. The residues in
ADH are
shown using the thicker line. The electron density map is from
the structure
and contoured^ at 1.0 S.D. of the map.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(1997,
272,
18558-18563)
copyright 1997.
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