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Title
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Structure of cyclodextrin glycosyltransferase complexed with a maltononaose inhibitor at 2.6 angstrom resolution. Implications for product specificity.
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Authors
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B.Strokopytov,
R.M.Knegtel,
D.Penninga,
H.J.Rozeboom,
K.H.Kalk,
L.Dijkhuizen,
B.W.Dijkstra.
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Ref.
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Biochemistry, 1996,
35,
4241-4249.
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PubMed id
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Abstract
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Crystals of the Y195F mutant of cyclodextrin glycosyltransferase from Bacillus
circulans strain 251 were subjected to a double soaking procedure, in which they
were first soaked in a solution containing the inhibitor acarbose and
subsequently in a solution containing maltohexaose. The refined structure of the
resulting protein-carbohydrate complex has final crystallographic and free
R-factors for data in the 8-2.6 angstrom resolution range of 15.0% and 21.5%,
respectively, and reveals that a new inhibitor, composed of nine saccharide
residues, is bound in the active site. The first four residues correspond to
acarbose and occupy the same subsites near the catalytic residues as observed in
the previously reported acarbose-enzyme complex [Strokopytov et al. (1995)
Biochemistry 34, 2234-2240]. An oliogosaccharide consisting of five glucose
residues has been coupled to the nonreducing end of acarbose. At the fifth
residue the polysaccharide chain makes a sharp turn, allowing it to interact
with residues Tyr89, Phe195, and Asn193 and a flexible loop formed by residues
145-148. On the basis of the refined model of the complex an explanation is
given for the product specificity of CGTases.
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