The same group of enzymes with different names: cyclomaltodextrinases, neopullulanases, and maltogenic amylases

Abstract

Three groups of enzymes, cyclomaltodextrinases (CDases), maltogenic amylases (MAases), and neopullulanases (NPases), are capable of hydrolyzing cyclomaltodextrins (CDs), pullulan, and starch. These enzymes hydrolyze CDs and starch to maltose as the main product and pullulan to panose by the cleavage of alpha-1,4-D-glycosidic bond. The multiple-substrate specificity of these enzymes is distinguished from the substrate specificity of typical alpha-amylases, which virtually are not able to hydrolyze CDs and pullulan. Over 20 enzymes denoted as cyclomaltodextrinase, maltogenic amylase, or neopullulanase are found in public databases, which share 40-86% sequence identity with each other. Now, the crystal structures of each of the three differently named enzymes are available: CDase of alkalophilic Bacillus sp. I-5, MAase of Thermus species, and NPases of Bacillus stearothermophilus. All of the three structures reveal the common domain-swapped dimeric unit. Furthermore, the active site is commonly a cleft between the central (alpha/beta)(8)-barrel domain and the N-terminal domain. These structural data and sequence alignment of the three groups of enzymes convincingly suggest that they are not different enough to preserve the different names and enzyme codes.