FUNCTIONAL STARCH-BINDING DOMAIN OF ASPERGILLUS GLUCOAMYLASE-I IN ESCHERICHIA-COLI

We have fused three starch-binding domains (SBD) encoding gene fragmen ts (residues 511-616, 495-616 and 481-616) of glucoamylase I (GAI) to the 3' end of the Escherichia coli malE gene encoding maltose-binding protein (MBP). The fusion proteins were produced in E. coli and were p urified by chromatography on cross-linked amylose. Factor X(a) digesti on of the fusion proteins resulted in the release of functional SBD fr agments which were separated from MBP on the basis of their differenti al binding to cross-linked amylose. The amino acid (aa) composition of the purified SBD fragments agreed with the respective amino acid comp ositions of GAI. The sizes of the SBD fragments were 11.9, 13.8 and 15 .6 kDa, respectively.