Properties and applications of starch-converting enzymes of the α-amylase family

Abstract

Starch is a major storage product of many economically important crops such as wheat, rice, maize, tapioca, and potato. A large-scale starch processing industry has emerged in the last century. In the past decades, we have seen a shift from the acid hydrolysis of starch to the use of starch-converting enzymes in the production of maltodextrin, modified starches, or glucose and fructose syrups. Currently, these enzymes comprise about 30% of the world's enzyme production. Besides the use in starch hydrolysis, starch-converting enzymes are also used in a number of other industrial applications, such as laundry and porcelain detergents or as anti-staling agents in baking. A number of these starch-converting enzymes belong to a single family: the alpha-amylase family or family13 glycosyl hydrolases. This group of enzymes share a number of common characteristics such as a (beta/alpha)(8) barrel structure, the hydrolysis or formation of glycosidic bonds in the alpha conformation, and a number of conserved amino acid residues in the active site. As many as 21 different reaction and product specificities are found in this family. Currently, 25 three-dimensional (3D) structures of a few members of the alpha-amylase family have been determined using protein crystallization and X-ray crystallography. These data in combination with site-directed mutagenesis studies have helped to better understand the interactions between the substrate or product molecule and the different amino acids found in and around the active site. This review illustrates the reaction and product diversity found within the alpha-amylase family, the mechanistic principles deduced from structure-function relationship structures, and the use of the enzymes of this family in industrial applications.

A remote but significant sequence homology between glycoside hydrolase clan GH‐H and family GH31

“…2) are even more prominent examples of such subtle sequence adjustment. The aspartate near the C-terminus of b7 is: (i) in GH-H an invariant catalytic site residue [3][4][5][6][7][8][9][10][11]; and (ii) in GH31 an invariant and important residue [23][24][25]. Structurally, however, the two aspartates do not correspond to each other (Fig.…”

“…Of the more than 100 GH families defined at present in CAZy, the typical starch hydrolases and related enzymes are found in families 13,14,15,31,57, 70 and 77 [3][4][5]. Family GH13 is well known as the a-amylase family and, together with GH70 and GH77, forms clan GH-H [6][7][8][9][10]. This analysis focuses on clan GH-H and family GH31.…”

“…The enzymes have almost 30 different specificities, such as cyclodextrin glucanotransferase, a-glucosidase, isoamylase, neopullulanase, branching enzyme, etc., in addition to a-amylase [3][4][5][6][7][8][9][10]. Further, three-dimensional structures are known for enzymes representing approximately 20 of these specificities.…”

“…Family GH70, in contrast, is believed to possess a circularly permuted version of the GH13-type (b/a) 8 -barrel [14]. Enzymes of the entire clan GH-H are characterised by several (from 4 to 7) conserved sequence regions [15,16] and a common catalytic machinery involving an aspartate in strand b4, a glutamate in strand b5, and an aspartate after strand b7 that are essential for activity [3][4][5][6][7][8][9][10][11]17]. These three constitute the only invariant residues in GH-H [18], aspartate at the b4-strand acting as catalytic nucleophile and the b5-strand glutamate as general acid/base catalyst [19].…”

Enzymatic properties and primary structures of two α-amylase isozymes from the Pacific abalone Haliotis discus hannai

“…This enzyme has been used for the degradation and saccharification of starch in the fields of food, bakery, paper, sugar and starch industries (Monfort et a., 1996;Pandey et al, 2000;Van der Maarel et al, 2002;Gupta et al, 2003). -Amylases distributes over bacteria, fungi, plants, invertebrates, and higher animals and many of these enzymes belong to glycoside-hydrolase-family 13 (GHF13) (Jensen and Olsen 1992;Henry et al, 1993;Iefuji et al, 1996;Le Moine et al, 1997;Koyama et al, 2000;Saxena et al, 2007;Tripathi et al, 2007;Hmidet et al, 2008;Elarbi et al, 2009;Nikapitiya et al, 2009).…”