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Title
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Solution structure of the granular starch binding domain of glucoamylase from Aspergillus niger by nuclear magnetic resonance spectroscopy.
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Authors
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K.Sorimachi,
A.J.Jacks,
M.F.Le Gal-Coëffet,
G.Williamson,
D.B.Archer,
M.P.Williamson.
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Ref.
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J Mol Biol, 1996,
259,
970-987.
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PubMed id
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Abstract
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The solution structure of the granular starch binding domain (SBD) of
glucoamylase 1 from Aspergillus niger has been determined by heteronuclear
multidimensional nuclear magnetic resonance spectroscopy and simulated
annealing. A total of 1092 nuclear Overhauser enhancement-derived 1H-1H distance
constraints, 137 dihedral constraints and 86 hydrogen bond constraints were
incorporated into an X-PLOR simulated annealing and refinement protocol. The
family of calculated structures shows a well defined beta-sheet structure
consisting of one parallel and six antiparallel pairs of beta-strands which
forms an open-sided beta-barrel. The root-mean-square deviation (rmsd) of 53
individual structures to the calculated average structure for the backbone atoms
of residues excluding the N terminus and two mobile loops is 0.57(+/-0.10) A
while the rmsd for backbone atoms in beta-strands is 0.45(+/-0.08) A. Structural
features of the SBD in solution are compared to the X-ray crystal structure of a
homologous domain of cyclodextrin glycosyltransferase (CGTase) in the free and
bound forms. Titration studies with two ligands, maltoheptaose and
beta-cyclodextrin, show the existence of two binding sites. Examination of the
tertiary structures shows these two sites to be at one end of the molecule on
opposite faces. The majority of residues showing the largest 1H and 15N chemical
shift changes are located in loop regions. Many residues implicated in binding,
based on these changes, are similar in location to previously identified binding
site residues in the crystal structures of CGTase. Overall, the shift changes
are small indicating that the SBD does not undergo large conformational changes
upon ligand binding.
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