GH13 amylosucrases and GH70 branching sucrases, atypical enzymes in their respective families

Abstract

Amylosucrases and branching sucrases are α-retaining transglucosylases found in the glycoside-hydrolase families 13 and 70, respectively, of the clan GH-H. These enzymes display unique activities in their respective families. Using sucrose as substrate and without mediation of nucleotide-activated sugars, amylosucrase catalyzes the formation of an α-(1 → 4) linked glucan that resembles amylose. In contrast, the recently discovered branching sucrases are unable to catalyze polymerization of glucosyl units as they are rather specific for dextran branching through α-(1 → 2) or α-(1 → 3) branching linkages depending on the enzyme regiospecificity. In addition, GH13 amylosucrases and GH70 branching sucrases are naturally promiscuous and can glucosylate different types of acceptor molecules including sugars, polyols, or flavonoids. Amylosucrases have been the most investigated glucansucrases, in particular to control product profiles or to successfully develop tailored α-transglucosylases able to glucosylate various molecules of interest, for example, chemically protected carbohydrates that are planned to enter in chemoenzymatic pathways. The structural traits of these atypical enzymes will be described and compared, and an overview of the potential of natural or engineered enzymes for glycodiversification and chemoenzymatic synthesis will be highlighted.

Molecular and Functional Study of a Branching Sucrase-Like Glucansucrase Reveals an Evolutionary Intermediate between Two Subfamilies of the GH70 Enzymes

“…KEYWORDS GH70 enzymes, glucansucrase, branching sucrase, insoluble glucan, Leuconostoc mesenteroides, intermediate E nzymes of glycoside hydrolase family 70 (GH70) are increasingly attracting attention for their potential in producing ␣-glucans with wide applications in food and feed products, as well as health care products (1-3). GH70 enzymes are structurally and mechanistically related to the GH13 (4, 5) and GH77 (4, 6) families, with which they form the GH-H clan (4,6) of glycoside hydrolases (5,7,8). To date, a total of 66 GH70 enzymes have been biochemically characterized, most of which are distributed in the genera Lactobacillus, Leuconostoc, Streptococcus, and Weissella (http://www.cazy.org/GH70 _characterized.html) (9).…”

“…To date, a total of 66 GH70 enzymes have been biochemically characterized, most of which are distributed in the genera Lactobacillus, Leuconostoc, Streptococcus, and Weissella (http://www.cazy.org/GH70 _characterized.html) (9). Crystallographic structures of these enzymes suggested that they adopt a unique U-shaped fold organized into five distinct structural domains, i.e., A, B, C, IV, and V (10)(11)(12), of which A, B, and C are shared by GH13 enzymes, suggesting an evolutionary relationship between these two families (5).…”

“…Historically, GH70 enzymes are mainly glucansucrases (GSs) that catalyze the synthesis of ␣-glucan homopolysaccharides from the sole substrate sucrose, and enzymes of this type have been widely investigated (5,7,13). According to the CAZy database (http://www.cazy.org/GH70.html; accessed 4 July 2017), most GH70 enzymes identified in lactic acid bacteria (LAB) are GSs (9).…”

Enzymatic synthesis of polysaccharide-based copolymers

“…[23][24][25] Of the GSs, dextransucrases (DS; E.C. 2.4.1.5; CAZy family GH70) catalyse the synthesis of dextrans that are α-glucans of molar masses ranging from 10 4 to 10 9 g mol −1 with at least 50% α(1 → 6) linkages and various branching points.…”

“…33,34 In addition to polymer formation, GSs can also transfer the glucosyl unit of sucrose to a large variety of carbohydrate acceptors, including mono-, di-and trisaccharides such as galactose, xylose, maltose, isomaltose, mannose, maltotriose, panose, cellobiose, nigerose, lactose, raffinose and melibiose, as well as aglycon molecules such as polyols or flavonoids. 25,[35][36][37][38][39] However, there are very few publications describing the glucosylation using GSs of oligosaccharides with a DP higher than 3. The first example of this involved the strict elongation of maltooligosaccharides (MOSs) with a DP between 2 and 8 by the GTF-I and GTF-S enzymes from S. mutans 6715 40 and the dextransucrase from L. mesenteroides NRRL B-512FM.…”