Archaeal and bacterial thermostable amylopullulanases: characteristic features and biotechnological applications

Abstract

Amylopullulanases are endoacting bifunctional enzymes capable of hydrolyzing α-1,4- and α-1,6-glycosidic linkages in starch, amylose, pullulan, amylopectin and related oligosaccharides. These enzymes possess single or dual active site(s) for cleaving α-1,4- and α-1,6-glycosidic bonds; the former are called amylopullulanases, and the latter, α-amylase-pullulanases. These are grouped into GH13 and GH57 families based on the architecture of the catalytic domain and the number of conserved sequence regions. The amylopullulanases/α-amylasepullulanases are produced by bacteria as well as archaea, and among them, thermophilic and hyperthermophilic species are the major producers. The thermostable amylopullulanases find application in one-step starch liquefaction-saccharification to form various sugar syrups and maltooligosaccharides. The starch saccharification process catalysed by amylopullulanases minimizes the use of other amylolytic enzymes, like α-amylase and glucoamylase, thereby reducing the cost of sugar syrups. The enzymes also find applications in bread making as an anti-stale and as a detergent additive.