Refined structure for the complex of d-gluco-dihydroacarbose with glucoamylase from Aspergillus awamori var. X100 to 2.2 Å resolution: dual conformations for extended inhibitors bound to the act
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文摘
The crystal structure at pH 4 of the complex of glucoamylase II(471) from Aspergillus awamori var. X100 with the pseudotetrasaccharide d-gluco-dihydroacarbose has been refined to an R-factor of 0.125 against data to 2.2 Å resolution. The first two residues of the inhibitor bind at a position nearly identical to those of the closely related inhibitor acarbose in its complex with glucoamylase at pH 6. However, the electron density bifurcates beyond the second residue of the d-gluco-dihydroacarbose molecule, placing the third and fourth residues together at two positions in the active site. The position of relatively low density (estimated occupancy of 35 % ) corresponds to the location of the third and fourth residues of acarbose in its complex with glucoamylase at pH 6. The position of high density (65 % occupancy) corresponds to a new binding mode of an extended inhibitor to the active site of glucoamylase. Presented are possible causes for the binding of d-gluco-dihydroacarbose in two conformations at the active site of glucoamylase at pH 4.
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