DOMAIN-E OF BACILLUS-MACERANS CYCLODEXTRIN GLUCANOTRANSFERASE - AN INDEPENDENT STARCH-BINDING DOMAIN

The starch-binding domains of glucoamylase I (SBD of GA-I) from Aspergillus awamori and of cyclodextrin glucanotransferase (domain E of CGTase) from Bacillus macerans were fused to the C-terminus of beta-galactosidase (beta-gal). The majority of the fusion proteins produced in Escherichia coli were found as inclusion bodies. Active fusion proteins were purified by partial solubilization of the inclusion bodies with 2 M urea followed by affinity chromatography. Adsorption isotherms of purified fusion proteins on corn starch and cross-linked amylose were generated. The beta-gal fusion proteins had similar affinities for cross-linked amylose and corn starch but significantly different saturation capacities on corn starch. The adsorption and elution data from the potato starch column as well as the adsorption isotherms of beta-gal-domain E fusion protein (BDE109) on corn starch and cross-linked amylose demonstrated that domain E of CGTase is an independent domain, which retained its starch-binding activity when separated from the other four (A-D) domains in CGTase. (C) 1995 John Wiley & Sons, Inc.