STRUCTURAL SIMILARITIES IN GLUCOAMYLASES BY HYDROPHOBIC CLUSTER-ANALYSIS

The model of the catalytic domain of Aspergillus awamori var. X100 glucoamylase was related to 14 other glucoamylase protein sequences belonging to five subfamilies. Structural features of the different sequences were revealed by multisequence alignment following hydrophobic cluster analysis. The alignment agreed with the hydrophobic microdomains, normally conserved throughout evolution, evaluated from the 3-D model. Saccharomyces and Clostridium glucoamylases lack the alpha-helix exterior to the catalytic domain. A different catalytic base was found in the Saccharomyces glucoamylase subfamily. The starch binding domain of fungal glucoamylases has identical structural features and substrate interacting residues as the C-terminal domain of models of Bacillus circulans cyclodextrin glucosyltransferases. Three putative N-glycosylation sites were found in the same turns in glucoamylases of different subfamilies. O-Glycosylation is present at different levels in the catalytic domain and in the linker between the catalytic and starch binding domains.