Characterization of a glucoamylase G2 from Aspergillus niger

Abstract

Peptide fragments were generated by enzymic or chemical degradation of the small form, G2, and the large form, G1, of Aspergillus niger glucoamylase (EC 3.1.2.3). The G2 form was either identical to residues Ala¹– Pro⁵¹² or to Ala¹– Ala⁵¹⁴ of the G1 polypeptide chain containing 616 amino acid residues. Structural analysis of the O-linked carbohydrates from the 70-amino-acid-residues long extensively glycosylated segment of G2 revealed no significant differences in the contents of single mannose and oligosaccharide units in comparison to the corresponding region of G1. The results suggest that the present G2 form has been generated by limited proteolysis of the larger G1. In contradistinction to this, a recently reported splicing out of an intervening sequence from G1 mRNA leads to a smaller mRNA coding for a G2 protein product with a different COOH-terminal sequence than the G2 form described in the present work [Boel et al. (1984) EMBO J. 3, 1097–1102].