Production and purification of a granular-starch-binding domain of glucoamylase 1 from Aspergillus niger

A domain of glucoamylase 1 from Aspergillus niger which binds to granular starch was produced by proteolytic digestion and purified to apparent homogeneity by extraction with corn starch followed by anion-exchange chromatography and gel filtration. The peptide has a molecular weight of 25,100, contains approximately 38% carbohydrate (w/w) and corresponds to residues 471-616 at the C-terminus of glucoamylase 1. The peptide bound to granular corn starch maximally at 1.08 nmol/mg starch. It inhibited the hydrolysis of granular starch by glucoamylase 1 but had no effect on the hydrolysis of starch in solution.