Amylolytic enzymes: Molecular aspects of their properties

The present review describes the structural features of alpha -amylase, bet a -amylase and glucoamylase that are the best known amylolytic enzymes. Alt hough they show similar function, i.e. catalysis of hydrolysis of alpha -gl ucosidic bonds in starch and related saccharides, they are quite different. alpha -amylase is the alpha --> alpha retaining glycosidase tit uses the r etaining mechanism), and P-amylase together with glucoamylase are the alpha --> beta inverting glycosidases (they use the inverting mechanism). While beta -amylase and glucoamylase form their own families 14 and 15, respectiv ely, in the sequence-based classification of glycoside hydrolases, alpha -a mylase belongs to a large dan of three families 13, 70 and 77 consisting of almost 30 different specificities. Structurally both alpha -amylase and be ta -amylase sank among the parallel (beta/alpha)(8)-barrel enzymes, glucoam ylase adopts the helical (alpha/alpha)(6)-barrel fold. The catalytic (beta/ alpha)(8)-barrels of alpha -amylase and beta -amylase differ from each othe r. The only common sequence-structural feature is the presence of the starc h-binding domain responsible for the binding and ability to digest raw star ch. It is, however, present in about 10 % of amylases and behaves as an ind ependent evolutionary module. A brief discussion on structure-function and structure-stability relationships of cr-amylases and related enzymes is als o provided.