Characterization of the catalytic and kinetic properties of a thermostable Thermoplasma acidophilum α-glucosidase and its transglucosylation reaction with arbutin

Glycoside hydrolases from (hyper)thermophilic archaea: structure, function, and applications

(Hyper)thermophilic archaeal glycosidases are enzymes that catalyze the hydrolysis of glycosidic bonds to break down complex sugars and polysaccharides at high temperatures. These enzymes have an unique structure that allows them to remain stable and functional in extreme environments such as hot springs and hydrothermal vents. This review provides an overview of the current knowledge and milestones on the structures and functions of (hyper)thermophilic archaeal glycosidases and their potential applications in various fields. In particular, this review focuses on the structural characteristics of these enzymes and how these features relate to their catalytic activity by discussing different types of (hyper)thermophilic archaeal glycosidases, including β-glucosidases, chitinase, cellulases and α-amylases, describing their molecular structures, active sites, and mechanisms of action, including their role in the hydrolysis of carbohydrates. By providing a comprehensive overview of (hyper)thermophilic archaeal glycosidases, this review aims to stimulate further research into these fascinating enzymes.

Evolutionary patterns of archaea predominant in acidic environment

BACKGROUND

Archaea of the order Thermoplasmatales are widely distributed in natural acidic areas and are amongst the most acidophilic prokaryotic organisms known so far. These organisms are difficult to culture, with currently only six genera validly published since the discovery of Thermoplasma acidophilum in 1970. Moreover, known great diversity of uncultured Thermoplasmatales represents microbial dark matter and underlines the necessity of efforts in cultivation and study of these archaea. Organisms from the order Thermoplasmatales affiliated with the so-called "alphabet-plasmas", and collectively dubbed "E-plasma", were the focus of this study. These archaea were found predominantly in the hyperacidic site PM4 of Parys Mountain, Wales, UK, making up to 58% of total metagenomic reads. However, these archaea escaped all cultivation attempts.

RESULTS

Their genome-based metabolism revealed its peptidolytic potential, in line with the physiology of the previously studied Thermoplasmatales isolates. Analyses of the genome and evolutionary history reconstruction have shown both the gain and loss of genes, that may have contributed to the success of the "E-plasma" in hyperacidic environment compared to their community neighbours. Notable genes among them are involved in the following molecular processes: signal transduction, stress response and glyoxylate shunt, as well as multiple copies of genes associated with various cellular functions; from energy production and conversion, replication, recombination, and repair, to cell wall/membrane/envelope biogenesis and archaella production. History events reconstruction shows that these genes, acquired by putative common ancestors, may determine the evolutionary and functional divergences of "E-plasma", which is much more developed than other representatives of the order Thermoplasmatales. In addition, the ancestral hereditary reconstruction strongly indicates the placement of Thermogymnomonas acidicola close to the root of the Thermoplasmatales.

CONCLUSIONS

This study has analysed the metagenome-assembled genome of "E-plasma", which denotes the basis of their predominance in Parys Mountain environmental microbiome, their global ubiquity, and points into the right direction of further cultivation attempts. The results suggest distinct evolutionary trajectories of organisms comprising the order Thermoplasmatales, which is important for the understanding of their evolution and lifestyle.

Insight into broad substrate specificity and synergistic contribution of a fungal α-glucosidase in Chinese Nong-flavor daqu

BACKGROUND

Chinese Nong-favor daqu, the presentative liquor starter of Baijiu, has been enriched with huge amounts of enzymes in degrading various biological macromolecules by openly man-made process for thousand years. According to previous metatranscriptomics analysis, plenty of α-glucosidases were identified to be active in NF daqu and played the key role in degrading starch under solid-state fermentation. However, none of α-glucosidases was characterized from NF daqu, and their actual functions in NF daqu were still unknown.

RESULTS

An α-glucosidase (NFAg31A, GH31-1 subfamily), the second highest expressed α-glucosidases in starch degradation of NF daqu, was directly obtained by heterologous expression in Escherichia coli BL21 (DE3). NFAg31A exhibited the highest sequence identities of 65.8% with α-glucosidase II from Chaetomium thermophilum, indicating its origin of fungal species, and it showed some similar features with homologous α-glucosidase IIs, i.e., optimal activity at pH ~ 7.0 and litter higher temperature of 45 ℃, well stability at 41.3 ℃ and a broad pH range of pH 6.0 to pH 10.0, and preference on hydrolyzing Glc-α1,3-Glc. Besides this preference, NFAg31A showed comparable activities on Glc-α1,2-Glc and Glc-α1,4-Glc, and low activity on Glc-α1,6-Glc, indicating its broad specificities on α-glycosidic substrates. Additionally, its activity was not stimulated by any of those detected metal ions and chemicals, and could be largely inhibited by glucose under solid-state fermentation. Most importantly, it exhibited competent and synergistic effects with two characterized α-amylases of NF daqu on hydrolyzing starch, i.e., all of them could efficiently degrade starch and malto-saccharides, two α-amylases showed advantage in degrading starch and long-chain malto-saccharides, and NFAg31A played the competent role with α-amylases in degrading short-chain malto-saccharides and the irreplaceable contribution in hydrolyzing maltose into glucose, thus alleviating the product inhibitions of α-amylases.

CONCLUSIONS

This study provides not only a suitable α-glucosidase in strengthening the quality of daqu, but also an efficient way to reveal roles of the complicated enzyme system in traditional solid-state fermentation. This study would further stimulate more enzyme mining from NF daqu, and promote their actual applications in solid-state fermentation of NF liquor brewing, as well as in other solid-state fermentation of starchy industry in the future.

Structural and functional analyses of Pcal_0917, an α-glucosidase from hyperthermophilic archaeon Pyrobaculum calidifontis

Genome analysis of Pyrobaculum calidifontis revealed the presence of α-glucosidase (Pcal_0917) gene. Structural analysis affirmed the presence of signature sequences of Type II α-glucosidases in Pcal_0917. We have heterologously expressed the gene and produced recombinant Pcal_0917 in Escherichia coli. Biochemical characteristics of the recombinant enzyme resembled to that of Type I α-glucosidases, instead of Type II. Recombinant Pcal_0917 existed in a tetrameric form in solution and displayed highest activity at 95 °C and pH 6.0, independent of any metal ions. A short heat-treatment at 90 °C resulted in a 35 % increase in enzyme activity. A slight structural shift was observed by CD spectrometry at this temperature. Half-life of the enzyme was >7 h at 90 °C. Pcal_0917 exhibited apparent V_max values of 1190 ± 5 and 3.9 ± 0.1 U/mg against p-nitrophenyl α-D-glucopyranoside and maltose, respectively. To the best of our knowledge, Pcal_0917 displayed the highest ever reported p-nitrophenyl α-D-glucopyranosidase activity among the characterized counterparts. Moreover, Pcal_0917 displayed transglycosylation activity in addition to α-glucosidase activity. Furthermore, in combination with α-amylase, Pcal_0917 was capable of producing glucose syrup from starch with >40 % glucose content. These properties make Pcal_0917 a potential candidate for starch hydrolyzing industry.

Valorization of Biomasses from Energy Crops for the Discovery of Novel Thermophilic Glycoside Hydrolases through Metagenomic Analysis

The increasing interest for environmentally friendly technologies is driving the transition from fossil-based economy to bioeconomy. A key enabler for circular bioeconomy is to valorize renewable biomasses as feedstock to extract high value-added chemicals. Within this transition the discovery and the use of robust biocatalysts to replace toxic chemical catalysts play a significant role as technology drivers. To meet both the demands, we performed microbial enrichments on two energy crops, used as low-cost feed for extremophilic consortia. A culture-dependent approach coupled to metagenomic analysis led to the discovery of more than 300 glycoside hydrolases and to characterize a new α-glucosidase from an unknown hyperthermophilic archaeon. Aglu1 demonstrated to be the most active archaeal GH31 on 4Np-α-Glc and it showed unexpected specificity vs. kojibiose, revealing to be a promising candidate for biotechnological applications such as the liquefaction/saccharification of starch.

Discovery of a Kojibiose Hydrolase by Analysis of Specificity-Determining Correlated Positions in Glycoside Hydrolase Family 65

The Glycoside Hydrolase Family 65 (GH65) is an enzyme family of inverting α-glucoside phosphorylases and hydrolases that currently contains 10 characterized enzyme specificities. However, its sequence diversity has never been studied in detail. Here, an in-silico analysis of correlated mutations was performed, revealing specificity-determining positions that facilitate annotation of the family’s phylogenetic tree. By searching these positions for amino acid motifs that do not match those found in previously characterized enzymes from GH65, several clades that may harbor new functions could be identified. Three enzymes from across these regions were expressed in E. coli and their substrate profile was mapped. One of those enzymes, originating from the bacterium Mucilaginibacter mallensis, was found to hydrolyze kojibiose and α-1,2-oligoglucans with high specificity. We propose kojibiose glucohydrolase as the systematic name and kojibiose hydrolase or kojibiase as the short name for this new enzyme. This work illustrates a convenient strategy for mapping the natural diversity of enzyme families and smartly mining the ever-growing number of available sequences in the quest for novel specificities.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Broad substrate specificity of a hyperthermophilic α-glucosidase from Pyrobaculum arsenaticum

Pyrobaculum arsenaticum is a hyperthermophilic archaeon that thrives at 95°C. This strain encodes a putative GH31 intracellular α-glucosidase (Pars_2044, PyAG) in its genome. The recombinant PyAG (rPyAG) was optimally expressed in Escherichia coli at 37°C for 4 h after IPTG induction. The purified rPyAG is a homotetrameric α-glucosidase that exhibited highly thermostable properties. Maximum p-nitrophenyl-α-D-glucopyranoside (pNPG) hydrolysis activity was observed at 90°C and pH 5.0. The enzyme mainly recognized the non-reducing end of the substrate, releasing the glucose unit. rPyAG also had broad substrate specificity, cleaving maltose (α-1,4-linkage), kojibiose (α-1,2-linkage), and nigerose (α-1,3-linkage) with similar efficiency. Based on these results, rPyAG can be used to modify health-relevant sugar conjugates linked by α-1,2- or α-1,3-bonds.

Synthesis of hexyl α-glucoside and α-polyglucosides by a novel Microbacterium isolate

Alkyl-glucosides and alkyl-polyglucosides are the new-generation biodegradable surfactants with good emulsifying and wetting properties. The α-forms of these glucosides occur in antibiotics and also stimulate nasal absorption of many drugs. In this paper, we report the synthesis of hexyl α-glucoside and α-polyglucosides using cell-bound α-glucosidase activity of a novel strain of Microbacterium paraoxydans. A number of cell-bound glycosyl hydrolase activities were detected in the isolate with the maximum hydrolytic activity of 180 IU g(-1) dry wt cells on p-nitrophenyl-α-D-glucopyranoside. In a micro-aqueous system, at a water activity of 0.69, 1.8 g l(-1) of hexyl α-glucoside (corresponding to about 25 % yield) was synthesized by whole cells with maltose and hexanol as substrates. The concentration was enhanced to 11 g l(-1) (~60 % yield) in a biphasic system at a water content of 60 %. (1)H and (13)C NMR spectra of the purified compound confirmed the synthesized product to be hexyl-α-D-glucopyranoside, while the presence of hexyl di- and tri-glucosides was confirmed by electrospray ionization mass spectrometry. The cell-driven synthesis makes this an extremely attractive alternative for synthesis of such compounds.

Identification and characterization of MalA in the maltose/maltodextrin operon of Sulfolobus acidocaldarius DSM639

A putative maltose/maltodextrin operon was found in the Sulfolobus acidocaldarius DSM639 genome. The gene cluster consisted of 7 genes (malA, trmB, amyA, malG, malF, malE, and malK). Here, we report the identification of MalA, which is responsible for the hydrolysis of maltose or maltodextrin to glucose in S. acidocaldarius. The transcription level of malA was increased 3-fold upon the addition of maltose or starch to the medium. Moreover, the α-glucosidase activity for maltose as a substrate in cell extracts of S. acidocaldarius DSM639 was also 11- and 10-fold higher during growth in YT medium (Brock's mineral salts, 0.1% [wt/vol] tryptone, and 0.005% [wt/vol] yeast extract) containing maltose or starch, respectively, than during growth on other sugars. The gene encoding MalA was cloned and expressed in S. acidocaldarius. The enzyme purified from the organism was a dodecamer in its active state and showed strong maltose-hydrolyzing activity at 100°C and pH 5.0. MalA was remarkably thermostable, with half-lives of 33.8 h, 10.6 h, and 1.8 h at 95°C, 100°C, and 105°C, respectively. Substrate specificity and kinetic studies of MalA with maltooligosaccharides indicated that MalA efficiently hydrolyzed maltose to maltopentaose, which is a typical characteristic of GH31-type α-glucosidases. However, glycogen or starch was not hydrolyzed. Reverse transcription-PCR, sugar uptake, and growth studies of the wild-type DSM639 and ΔmalEFG mutant on different sugars demonstrated that MalA located in the mal operon gene cluster is involved in maltose and starch metabolism in S. acidocaldarius.

Structural enzymology of Cellvibrio japonicus Agd31B protein reveals α-transglucosylase activity in glycoside hydrolase family 31

The metabolism of the storage polysaccharides glycogen and starch is of vital importance to organisms from all domains of life. In bacteria, utilization of these α-glucans requires the concerted action of a variety of enzymes, including glycoside hydrolases, glycoside phosphorylases, and transglycosylases. In particular, transglycosylases from glycoside hydrolase family 13 (GH13) and GH77 play well established roles in α-glucan side chain (de)branching, regulation of oligo- and polysaccharide chain length, and formation of cyclic dextrans. Here, we present the biochemical and tertiary structural characterization of a new type of bacterial 1,4-α-glucan 4-α-glucosyltransferase from GH31. Distinct from 1,4-α-glucan 6-α-glucosyltransferases (EC 2.4.1.24) and 4-α-glucanotransferases (EC 2.4.1.25), this enzyme strictly transferred one glucosyl residue from α(1→4)-glucans in disproportionation reactions. Substrate hydrolysis was undetectable for a series of malto-oligosaccharides except maltose for which transglycosylation nonetheless dominated across a range of substrate concentrations. Crystallographic analysis of the enzyme in free, acarbose-complexed, and trapped 5-fluoro-β-glucosyl-enzyme intermediate forms revealed extended substrate interactions across one negative and up to three positive subsites, thus providing structural rationalization for the unique, single monosaccharide transferase activity of the enzyme.

Biotechnological production of arbutins (α- and β-arbutins), skin-lightening agents, and their derivatives

Arbutins (α- and β-arbutins) are glycosylated hydroquinones that are commercially used in the cosmetic industry. These compounds have an inhibitory function against tyrosinase, a critical enzyme for generating pigments, which leads to the prevention of melanin formation, resulting in a whitening effect on the skin. Although β-arbutin is found in various plants including bearberry, wheat, and pear, α-arbutin and other arbutin derivatives are synthesized by chemical and enzymatic methods. This article presents a mini-review of recent studies on the production of α-arbutin and other α- and β-arbutin derivatives via enzymatic bioconversion methods. In addition, the structures of α- and β-arbutin derivatives and their biological activities are discussed. The catalytic characteristics of various enzymes used in the biosynthesis of arbutin derivatives are also reviewed.