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PDBsum entry 1ava
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Hydrolase inhibition
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PDB id
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1ava
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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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Barley alpha-Amylase bound to its endogenous protein inhibitor basi: crystal structure of the complex at 1.9 a resolution.
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Authors
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F.Vallée,
A.Kadziola,
Y.Bourne,
M.Juy,
K.W.Rodenburg,
B.Svensson,
R.Haser.
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Ref.
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Structure, 1998,
6,
649-659.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: Barley alpha-amylase is a 45 kDa enzyme which is involved in starch
degradation during barley seed germination. The released sugars provide the
plant embryo with energy for growth. The major barley alpha-amylase isozyme
(AMY2) binds with high affinity to the endogenous inhibitor BASI (barley
alpha-amylase/subtilisin inhibitor) whereas the minor isozyme (AMY1) is not
inhibited. BASI is a 19.6 kDa bifunctional protein that can simultaneously
inhibit AMY2 and serine proteases of the subtilisin family. This inhibitor may
therefore prevent degradation of the endosperm starch during premature sprouting
and protect the seed from attack by pathogens secreting proteases. RESULTS: The
crystal structure of AMY2 in complex with BASI was determined and refined at 1.9
A resolution. BASI consists of a 12-stranded beta-barrel structure which belongs
to the beta-trefoil fold family and inhibits AMY2 by sterically occluding access
of the substrate to the active site of the enzyme. The AMY2-BASI complex is
characterized by an unusual completely solvated calcium ion located at the
protein-protein interface. CONCLUSIONS: The AMY2-BASI complex represents the
first reported structure of an endogenous protein-protein complex from a higher
plant. The structure of the complex throws light on the strict specificity of
BASI for AMY2, and shows that domain B of AMY2 contributes greatly to the
specificity of enzyme-inhibitor recognition. In contrast to the
three-dimensional structures of porcine pancreatic alpha-amylase in complex with
proteinaceous inhibitors, the AMY2-BASI structure reveals that the catalytically
essential amino acid residues of the enzyme are not directly bound to the
inhibitor. Binding of BASI to AMY2 creates a cavity, exposed to the external
medium, that is ideally shaped to accommodate an extra calcium ion. This feature
may contribute to the inhibitory effect, as the key amino acid sidechains of the
active site are in direct contact with water molecules which are in turn ligated
to the calcium ion.
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Figure 5.
Figure 5. Sequence comparison of AMY1 and AMY2 relevant to
the interface area of the AMY2-BASI complex. Residues involved
in the interaction with BASI are indicated by yellow rectangles.
Calcium ligands are marked by pink, orange and blue circles for
Ca500, Ca501 and Ca502, respectively. Non-conservative
substitutions are indicated with red squares. Bold and
underlined residues designate sidechain substitutions between
AMY1 and AMY2 for residues in interaction with BASI. Domain B is
outlined in green, whereas domain A is shaded in blue.
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The above figure is
reprinted
by permission from Cell Press:
Structure
(1998,
6,
649-659)
copyright 1998.
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Secondary reference #1
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Title
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Characterization, Crystallization and preliminary X-Ray crystallographic analysis of the complex between barley alpha-Amylase and the bifunctional alpha-Amylase/subtilisin inhibitor from barley seeds.
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Authors
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F.Vallée,
A.Kadziola,
Y.Bourne,
J.Abe,
B.Svensson,
R.Haser.
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Ref.
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J Mol Biol, 1994,
236,
368-371.
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PubMed id
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