X-ray structure of Novamyl, the five-domain "maltogenic" alpha-amylase from Bacillus stearothermophilus: maltose and acarbose complexes at 1.7A resolution.

摘要: The three-dimensional structure of the Bacillus stearothermophilus "maltogenic" alpha-amylase, Novamyl, has been determined by X-ray crystallography at a resolution 1.7 A. Unlike conventional alpha-amylases from glycoside hydrolase family 13, Novamyl exhibits five-domain more usually associated with cyclodextrin glycosyltransferase. Complexes enzyme both maltose and inhibitor acarbose have characterized. In complex, two molecules are found in -1 to -2 +2 +3 subsites active site, on C E domains. C-domain occupies position identical one previously observed circulans CGTase [Lawson, C. L., et al. (1994) J. Mol. Biol. 236, 590-600], suggesting that plays genuine biological role saccharide binding. acarbose-maltose tetrasaccharide is as an extended hexasaccharide species, bound -3 subsites. transition state mimicking pseudosaccharide subsite 2H3 half-chair conformation, expected. site lies open gully, fully consistent its ability perform internal cleavage via endo opposed exo activity.