The evolution of starch-binding domain

Amylolytic enzymes belonging to three distinct families of glycosidases (13 , 14, 15) contain the starch-binding domain (SBD) positioned almost exclusi vely at the C-terminus, Detailed analysis of all available SBD sequences fr om 43 different amylases revealed its independent evolutionary behaviour wi th regard to the catalytic domains. In the evolutionary tree based on seque nce alignment of the SBDs, taxonomy is respected so that fungi and actinomy cetes form their own separate parts surrounded by bacteria that are also cl ustered according to taxonomy. The only known N-terminal SBD from Rhizopus oryzae glucoamylase is on the longest branch separated from all C-terminal SBDs. The 3-dimensional (3-D) structures of fungal glucoamylase and bacteri al CGTase SBDs are compared and used to discuss the interesting SBD evoluti on. (C) 1999 Federation of European Biochemical Societies.