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.