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PDBsum entry 1itc
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* Residue conservation analysis
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Enzyme class:
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E.C.3.2.1.2
- beta-amylase.
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Reaction:
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Hydrolysis of 1,4-alpha-glucosidic linkages in polysaccharides so as to remove successive maltose units from the non-reducing ends of the chains.
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DOI no:
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Biochemistry
42:5574-5581
(2003)
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PubMed id:
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Crystal structure of a catalytic site mutant of beta-amylase from Bacillus cereus var. mycoides cocrystallized with maltopentaose.
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H.Miyake,
G.Kurisu,
M.Kusunoki,
S.Nishimura,
S.Kitamura,
Y.Nitta.
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ABSTRACT
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The X-ray crystal structure of a catalytic site mutant of beta-amylase, E172A
(Glu172 --> Ala), from Bacillus cereus var. mycoides complexed with a
substrate, maltopentaose (G5), and the wild-type enzyme complexed with maltose
were determined at 2.1 and 2.0 A resolution, respectively. Clear and continuous
density corresponding to G5 was observed in the active site of E172A, and thus,
the substrate, G5, was not hydrolyzed. All glucose residues adopted a relaxed
(4)C(1) conformation, and the conformation of the maltose unit for Glc2 and Glc3
was much different from those of other maltose units, where each glucose residue
of G5 is named Glc1-Glc5 (Glc1 is at the nonreducing end). A water molecule was
observed 3.3 A from the C1 atom of Glc2, and 3.0 A apart from the OE1 atom of
Glu367 which acts as a general base. In the wild-type enzyme-maltose complex,
two maltose molecules bind at subsites -2 and -1 and at subsites +1 and +2 in
tandem. The conformation of the maltose molecules was similar to that of the
condensation product of soybean beta-amylase, but differed from that of G5 in
E172A. When the substrate flips between Glc2 and Glc3, the conformational energy
of the maltose unit was calculated to be 20 kcal/mol higher than that of the cis
conformation by MM3. We suggest that beta-amylase destabilizes the bond that is
to be broken in the ES complex, decreasing the activation energy, DeltaG(++),
which is the difference in free energy between this state and the transition
state.
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Literature references that cite this PDB file's key reference
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PubMed id
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Reference
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K.Karaveg,
A.Siriwardena,
W.Tempel,
Z.J.Liu,
J.Glushka,
B.C.Wang,
and
K.W.Moremen
(2005).
Mechanism of class 1 (glycosylhydrolase family 47) {alpha}-mannosidases involved in N-glycan processing and endoplasmic reticulum quality control.
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J Biol Chem,
280,
16197-16207.
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PDB code:
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The most recent references are shown first.
Citation data come partly from CiteXplore and partly
from an automated harvesting procedure. Note that this is likely to be
only a partial list as not all journals are covered by
either method. However, we are continually building up the citation data
so more and more references will be included with time.
Where a reference describes a PDB structure, the PDB
code is
shown on the right.
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Links
