Glycosyl hydrolase families 32 and 68, which for the clan GH-J. This glycosyl hydrolase family clan J (according to carbohydrate-active enzymes database (CAZY)) includes family 32 (GH32) and 68 (GH68). The overall sequence homology between the two families is low (<15% identity), but common sequence motifs have been identified. GH32 enzymes are invertases that also include other fructofuranosidases such as inulinase (EC 3.2.1.7), exo-inulinase (EC 3.2.1.80), levanase (EC 3.2.1.65), and transfructosidases such sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99), fructan:fructan 1-fructosyltransferase (EC 2.4.1.100), sucrose:fructan 6-fructosyltransferase (EC 2.4.1.10), fructan:fructan 6G-fructosyltransferase (EC 2.4.1.243) and levan fructosyltransferases (EC 2.4.1.-). GH32 enzymes cleave sucrose into fructose and glucose via beta-fructofuranosidase activity, producing invert sugar that is a mixture of dextrorotatory D-glucose and levorotatory D-fructose, thus named invertase (EC 3.2.1.26). GH68 consists of frucosyltransferases (FTFs) that include levansucrase (EC 2.4.1.10); beta-fructofuranosidase (EC 3.2.1.26); inulosucrase (EC 2.4.1.9), all of which use sucrose as their preferential donor substrate. A common structural feature of all these enzymes is a 5-bladed beta-propeller domain, similar to GH43, that contains the catalytic acid and catalytic base. A long V-shaped groove, partially enclosed at one end, forms a single extended substrate-binding surface across the face of the propeller.

Glycosyl hydrolase families: GH43, GH62, GH32, GH68. Members of the glycosyl hydrolase families 32, 43, 62 and 68 (GH32, GH43, GH62, GH68) all possess 5-bladed beta-propeller domains and comprise clans F and J, as classified by the carbohydrate-active enzymes database (CAZY). Clan F consists of families GH43 and GH62. GH43 includes beta-xylosidases, beta-xylanases, alpha-L-arabinases, and alpha-L-arabinofuranosidases, using aryl-glycosides as substrates, while family GH62 contains alpha-L-arabinofuranosidases (EC 3.2.1.55) that specifically cleave either alpha-1,2 or alpha-1,3-L-arabinofuranose sidechains from xylans. These are inverting enzymes (i.e. they invert the stereochemistry of the anomeric carbon atom of the substrate) that have an aspartate as the catalytic general base, a glutamate as the catalytic general acid and another aspartate that is responsible for pKa modulation and orienting the catalytic acid. Clan J consists of families GH32 and GH68. GH32 comprises sucrose-6-phosphate hydrolases, invertases, inulinases, levanases, eukaryotic fructosyltransferases, and bacterial fructanotransferases while GH68 consists of frucosyltransferases (FTFs) that include levansucrase (EC 2.4.1.10); beta-fructofuranosidase (EC 3.2.1.26); inulosucrase (EC 2.4.1.9), while GH68 consists of frucosyltransferases (FTFs) that include levansucrase (EC 2.4.1.10); beta-fructofuranosidase (EC 3.2.1.26); inulosucrase (EC 2.4.1.9), all of which use sucrose as their preferential donor substrate. Members of this clan are retaining enzymes (i.e. they retain the configuration at anomeric carbon atom of the substrate) that catalyze hydrolysis in two steps involving a covalent glycosyl enzyme intermediate: an aspartate located close to the N-terminus acts as the catalytic nucleophile and a glutamate acts as the general acid/base; a conserved aspartate residue in the Arg-Asp-Pro (RDP) motif stabilizes the transition state. Structures of all families in the two clans manifest a funnel-shaped active site that comprises two subsites with a single route for access by ligands.

Glycosyl hydrolase family 68, includes levansucrase, beta-fructofuranosidase and inulosucrase. Glycosyl hydrolase family 68 (GH68) consists of frucosyltransferases (FTFs) that include levansucrase (EC 2.4.1.10), beta-fructofuranosidase (EC 3.2.1.26) and inulosucrase (EC 2.4.1.9), all of which use sucrose as their preferential donor substrate. Levansucrase, also known as beta-D-fructofuranosyl transferase, catalyzes the transfer of the sucrose fructosyl moiety to a growing levan chain. Similarly, inulosucrase catalyzes long inulin-type of fructans, and beta-fructofuranosidases create fructooligosaccharides (FOS). However, in the absence of high fructan/sucrose ratio, some GH68 enzymes can also use fructan as donor substrate. GH68 retaining enzymes (i.e. they retain the configuration at anomeric carbon atom of the substrate) catalyze hydrolysis in two steps involving a covalent glycosyl enzyme intermediate: an aspartate located close to the N-terminus acts as the catalytic nucleophile and a glutamate acts as the general acid/base; a conserved aspartate residue in the Arg-Asp-Pro (RDP) motif stabilizes the transition state. A common structural feature of all these enzymes is a 5-bladed beta-propeller domain, similar to GH43, that contains the catalytic acid and catalytic base. A long V-shaped groove, partially enclosed at one end, forms a single extended substrate-binding surface across the face of the propeller. Biotechnological applications of these enzymes include use of inulin in inexpensive production of rich fructose syrups as well as use of FOS as health-promoting pre-biotics.

Levansucrase/Invertase. This Pfam family consists of the glycosyl hydrolase 68 family, including several bacterial levansucrase enzymes, and invertase from zymomonas.