STRUCTURAL SIMILARITIES IN GLUCOAMYLASES BY HYDROPHOBIC CLUSTER-ANALYSIS

The model of the catalytic domain of Aspergillus awamori var. X100 glu coamylase was related to 14 other glucoamylase protein sequences belon ging to five subfamilies. Structural features of the different sequenc es were revealed by multisequence alignment following hydrophobic clus ter 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 exte rior 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 ci rculans cyclodextrin glucosyltransferases. Three putative N-glycosylat ion sites were found in the same turns in glucoamylases of different s ubfamilies. O-Glycosylation is present at different levels in the cata lytic domain and in the linker between the catalytic and starch bindin g domains.