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PDBsum entry 1so0
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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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Molecular structure of human galactose mutarotase.
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Authors
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J.B.Thoden,
D.J.Timson,
R.J.Reece,
H.M.Holden.
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Ref.
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J Biol Chem, 2004,
279,
23431-23437.
[DOI no: ]
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PubMed id
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Abstract
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Galactose mutarotase catalyzes the conversion of beta-d-galactose to
alpha-d-galactose during normal galactose metabolism. The enzyme has been
isolated from bacteria, plants, and animals and is present in the cytoplasm of
most cells. Here we report the x-ray crystallographic analysis of human
galactose mutarotase both in the apoform and complexed with its substrate,
beta-d-galactose. The polypeptide chain folds into an intricate array of 29
beta-strands, 25 classical reverse turns, and 2 small alpha-helices. There are
two cis-peptide bonds at Arg-78 and Pro-103. The sugar ligand sits in a shallow
cleft and is surrounded by Asn-81, Arg-82, His-107, His-176, Asp-243, Gln-279,
and Glu-307. Both the side chains of Glu-307 and His-176 are in the proper
location to act as a catalytic base and a catalytic acid, respectively. These
residues are absolutely conserved among galactose mutarotases. To date, x-ray
models for three mutarotases have now been reported, namely that described here
and those from Lactococcus lactis and Caenorhabditis elegans. The molecular
architectures of these enzymes differ primarily in the loop regions connecting
the first two beta-strands. In the human protein, there are six extra residues
in the loop compared with the bacterial protein for an approximate longer length
of 9 A. In the C. elegans protein, the first 17 residues are missing, thereby
reducing the total number of beta-strands by one.
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Figure 2.
FIG. 2. Structure of human galactose mutarotase. A ribbon
representation of the three-dimensional architecture exhibited
by the apoenzyme is shown in a. For clarity, only the major
strands of the  -sheet are displayed.
Asterisks indicate the positions of cis-Arg-78 and cis-Pro-103.
The location of the active site is depicted in b as a
space-filling representation. Note that the 3-, 4-, and
6-hydroxyl groups of galactose, from left to right and indicated
by the red spheres, are solvent-exposed. The view is
approximately the same as displayed in a.
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Figure 3.
FIG. 3. The active site for human galactose mutarotase. A
close-up stereo view of those amino acid residues involved in
sugar binding is displayed in a. The color coding for the ribbon
representation is the same as in Fig. 2. The sugar is
highlighted in grayish bonds. Possible hydrogen bonding
interactions between the protein and the ligand are shown
schematically in b. The dotted lines indicate distances equal to
or below 3.2 Å.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
23431-23437)
copyright 2004.
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