GLUCOAMYLASE STRUCTURAL, FUNCTIONAL, AND EVOLUTIONARY RELATIONSHIPS

To correlate structural features with glucoamylase properties, a struc ture-based multisequence alignment was constructed using information f rom catalytic and starch-binding domain models, The catalytic domain i s composed of three hydrophobic folding units, the most labile and lea st hydrophobic of them being missing in the most stable glucoamylase, The role of O-glycosylation in stabilizing the most hydrophobic foldin g unit, the only one where thermostabilizing mutations with unchanged activity have been made, is described, Differences in both length and composition of interhelical loops are correlated with stability and se lectivity characteristics, Two new glucoamylase subfamilies are define d by using homology criteria, Protein parsimony analysis suggests an a ncient bacterial origin for the glucoamylase gene, Increases in length of the belt surrounding the active site, degree of O-glycosylation, a nd length of the linker probably correspond to evolutionary steps that increase stability and secretion levels of Aspergillus-related glucoa mylases. (C) 1997 Wiley-Liss, Inc.