A GH57 4-α-glucanotransferase of hyperthermophilic origin with potential for alkyl glycoside production

Production of Large-Ring Cyclodextrins by Amylomaltases

Amylomaltase is a well-known glucan transferase that can produce large ring cyclodextrins (LR-CDs) or so-called cycloamyloses via cyclization reaction. Amylomaltases have been found in several microorganisms and their optimum temperatures are generally around 60–70 °C for thermostable amylomaltases and 30–45 °C for the enzymes from mesophilic bacteria and plants. The optimum pHs for mesophilic amylomaltases are around pH 6.0–7.0, while the thermostable amylomaltases are generally active at more acidic conditions. Size of LR-CDs depends on the source of amylomaltases and the reaction conditions including pH, temperature, incubation time, and substrate. For example, in the case of amylomaltase from Corynebacterium glutamicum, LR-CD productions at alkaline pH or at a long incubation time favored products with a low degree of polymerization. In this review, we explore the synthesis of LR-CDs by amylomaltases, structural information of amylomaltases, as well as current applications of LR-CDs and amylomaltases.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

New groups of protein homologues in the α-amylase family GH57 closely related to α-glucan branching enzymes and 4-α-glucanotransferases

The glycoside hydrolase family GH57 is known as the second α-amylase family. Its main characteristics are as follows: (i) employing the retaining reaction mechanism; (ii) adopting the (β/α)₇-barrel (the incomplete TIM-barrel) with succeeding bundle of α-helices as the catalytic domain; (iii) sharing the five conserved sequence regions (CSRs) exhibiting the sequence fingerprints of the individual enzyme specificities; and (iv) using the catalytic machinery consisting of glutamic acid (the catalytic nucleophile) and aspartic acid (the proton donor) positioned at strands β4 (CSR-3) and β7 (CSR-4) of the (β/α)₇-barrel domain, respectively. Several years ago, a group of hypothetical proteins closely related to the specificity of α-amylase was revealed, the so-called α-amylase-like homologues, the members of which lack either one or even both catalytic residues. The novelty of the present study lies in delivering two additional groups of the "like" proteins that are homologues of α-glucan-branching enzyme (GBE) and 4-α-glucanotransferase (4AGT) specificities. Based on a recently published in silico analysis of more than 1600 family GH57 sequences, 13 GBE-like and 18 4AGT-like proteins from unique sources were collected and analyzed in a detail with respect to their taxonomical origin, sequence and structural features as well as evolutionary relationships. This in silico study could accelerate the efforts leading to experimental revealing the real function of the enzymes-like proteins in the α-amylase family GH57.

An ultra-stable glucanotransferase-cum-exoamylase from the hyperthermophile archaeon Thermococcus onnurineus

The genome of the hyperthermophile archaeon Thermococcus onnurineus (strain NA1) encodes a 652 residues-long putative 4-α-glucanotransferase of the GH 57 family which we have expressed in Escherichia coli. The enzyme (TonAmyGT) appears to remove glucose from the reducing end of a donor glucan and transfers it to the non-reducing end of an acceptor glucan, creating a pool of oligosaccharides through disproportionation of any substrate maltooligosaccharide, with maltose acting substantively as the smallest donor glucan as well as the smallest acceptor glucan. Additionally, glucose is also cleaved from maltooligosaccharides and released into solution without being transferred to an acceptor, causing the enzyme to function as an exo-amylase (which can digest starch) in addition to its activity as a glucanotransferase. TonAmyGT functions over a broad range of temperature (20-100 °C) and pH (4.0-9.0), and shows extreme resistance to chemical and thermal denaturation, displaying a melting temperature of 104 °C, at a pressure of 35 psi, in a differential scanning calorimeter. An interesting characteristic is that the glucanotransferase activity shows feedback inhibition through glucose (which the enzyme itself generates), indicating that the exo-amylase and glucanotransferase activities regulate each other.

Transglycosylation Properties of a Novel α-1,4-Glucanotransferase from Bacteroides thetaiotaomicron and Its Application in Developing an α-Glucosidase-Specific Inhibitor

In this study, α-glucanotransferase from Bacteroides thetaiotaomicron was expressed in Escherichia coli and characterized. Conserved amino-acid sequence alignment showed that Bacteroides thetaiotaomicron α-glucanotransferase (BtαGTase) belongs to the glycoside hydrolase family 77. The enzyme exhibited optimal catalytic activity at 60°C and pH 3.0. BtαGTase catalyzed transglycosylation reactions that produced only glycosyl or maltosyl transfer products, which are preferable for the generation of transglycosylated products with high yield. The 1-deoxynojirimycin (DNJ) glycosylation product G1-DNJ was generated using BtαGTase, and the inhibitory effect of G1-DNJ was analyzed. A kinetic study of inhibition revealed that G1-DNJ inhibited α-glucosidase to a greater extent than did DNJ but did not show any inhibitory effects towards α-amylase, suggesting that G1-DNJ is a potential candidate for the prevention of diabetes.

In silico analysis of the α-amylase family GH57: eventual subfamilies reflecting enzyme specificities

Glycoside hydrolases (GHs) have been classified in the CAZy database into 153 GH families. Currently, there might be four α-amylase families: the main family GH13, the family GH57 with related GH119 and, eventually, also GH126. The family GH57 was established in 1996 as the second and smaller α-amylase family. In addition to α-amylase, it contains 4-α-glucanotransferase, α-glucan branching enzyme, amylopullulanase, dual-specificity amylopullulanase–cyclomaltodextrinase, non-specified amylase, maltogenic amylase and α-galactosidase. The family GH57 enzymes employ the retaining reaction mechanism, share five typical conserved sequence regions and possess catalytic (β/α)₇-barrel succeeded by a four-helix bundle with the catalytic machinery consisting of catalytic nucleophile and proton donor (glutamic acid and aspartic acid at strands β4 and β7, respectively). The present bioinformatics study delivers a detailed sequence comparison of 1602 family GH57 sequences with the aim to highlight the uniqueness of each enzyme’s specificity and all eventual protein groups. This was achieved by creating the evolutionary tree focused on both the enzyme specificities and taxonomical origin. The substantial increase of numbers of sequences from recent comparisons done more than 5 years ago has allowed to refine the details of the sequence logos for the individual enzyme specificities. The study identifies a new evolutionary distinct group of α-galactosidase-related enzymes with until-now-undefined enzyme specificity but positioned on the evolutionary tree on a branch adjacent to α-galactosidases. The specificity of α-galactosidase is, moreover, the only one of the entire family GH57 for which there is no structural support for the proposal of the proton donor based on sequence analysis. The analysis also suggests a few so-called “like” protein groups related to some family GH57 enzyme specificities but lacking one or both catalytic residues.