Most forms of the enzyme can rapidly hydrolyse 1,6-alpha-D-glucosidic bonds when the next bond in the sequence is 1,4, and some preparations of this enzyme hydrolyse 1,6- and 1,3-alpha-D-glucosidic bonds in other polysaccharides. This entry covers all such enzymes acting on polysaccharides more rapidly than on oligosaccharides. EC 3.2.1.20 alpha-glucosidase, from mammalian intestine, can catalyse similar reactions.
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REACTION
REACTION DIAGRAM
COMMENTARY
ORGANISM
UNIPROT
LITERATURE
Hydrolysis of terminal (1->4)-linked alpha-D-glucose residues successively from non-reducing ends of the chains with release of beta-D-glucose
the enzyme catalyses the cleavage of alpha-1,4- and alpha-1,6-glycosidic bonds. Glucoamylases use a classical acid/base Koshland-type inverting mechanism, releasing alpha-glucose from the nonreducing end of an alpha-glucan chain
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SYSTEMATIC NAME
IUBMB Comments
4-alpha-D-glucan glucohydrolase
Most forms of the enzyme can rapidly hydrolyse 1,6-alpha-D-glucosidic bonds when the next bond in the sequence is 1,4, and some preparations of this enzyme hydrolyse 1,6- and 1,3-alpha-D-glucosidic bonds in other polysaccharides. This entry covers all such enzymes acting on polysaccharides more rapidly than on oligosaccharides. EC 3.2.1.20 alpha-glucosidase, from mammalian intestine, can catalyse similar reactions.
binding structure, overview. Found in the active sites of both independent monomers. In both monomers an acarbose molecule is fitted and refined, assuming full occupancy
the relative orientation between the carbohydrate-binding domain (CBM) and the catalytic domain is flexible, as the domains can adopt different orientations independently of ligand binding, suggesting a role as an anchor to increase the contact time and the relative concentration of substrate near the active site. The model of enzyme HrGA with two molecules in the asymmetric unit includes residues 29-616 and up to seven N-glycosylation sites and has acarbose bound in the active site. The C-terminal CBM adopts the well known beta-sandwich motif, which is a hallmark of carbohydrate-binding modules
glucoamylases consist of a catalytic domain and a carbohydrate-binding domain (CBM), with the latter being important for the interaction with the polymeric substrate. The relative orientation between the carbohydrate-binding domain (CBM) and the catalytic domain is flexible, as the domains can adopt different orientations independently of ligand binding, suggesting a role as an anchor to increase the contact time and the relative concentration of substrate near the active site. The model of enzyme HrGA with two molecules in the asymmetric unit includes residues 29-616 and up to seven N-glycosylation sites and has acarbose bound in the active site. The C-terminal CBM adopts the well known beta-sandwich motif, which is a hallmark of carbohydrate-binding modules
the model of enzyme HrGA with two molecules in the asymmetric unit includes residues 29-616 and up to seven N-glycosylation sites and has acarbose bound in the active site. The full-length structure of HrGA shows extensive N-glycosylation, where the resolved sites are at Asn99, Asn200, Asn427, Asn500, Asn514, Asn528 and Asn587. Asn200 is the only site that shows branching of the glycosylation chain
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CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
purified recombinant enzyme, sitting drop vapour diffusion method, mixing of 150 nl of 37 mg/ml protein in 20 mM sodium acetate, pH 5.0, with 150 nl of reservoir solution containing 60% Tacsimate, pH 7.0, 20°C, X-ray diffraction structure determination and analysis at 3.6 A resolution, molecular replacement using the catalytic domain of Aspergillus awamori glucoamylase as a search model (PDB entry 1glm)
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PURIFICATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
recombinant enzyme from Aspergillus niger strain MBin118 by alpha-cyclodextrin affinity chromatography, elution with beta-cyclodextrin, followed by dialysis, to homogeneity