Multiple sugar binding sites in alpha-glucosidase

Inhibitory Activity and Mechanism Investigation of Hypericin as a Novel α-Glucosidase Inhibitor

α-glucosidase is a major enzyme that is involved in starch digestion and type 2 diabetes mellitus. In this study, the inhibition of hypericin by α-glucosidase and its mechanism were firstly investigated using enzyme kinetics analysis, real-time interaction analysis between hypericin and α-glucosidase by surface plasmon resonance (SPR), and molecular docking simulation. The results showed that hypericin was a high potential reversible and competitive α-glucosidase inhibitor, with a maximum half inhibitory concentration (IC₅₀) of 4.66 ± 0.27 mg/L. The binding affinities of hypericin with α-glucosidase were assessed using an SPR detection system, which indicated that these were strong and fast, with balances dissociation constant (KD) values of 6.56 × 10⁻⁵ M and exhibited a slow dissociation reaction. Analysis by molecular docking further revealed that hydrophobic forces are generated by interactions between hypericin and amino acid residues Arg-315 and Tyr-316. In addition, hydrogen bonding occurred between hypericin and α-glucosidase amino acid residues Lys-156, Ser-157, Gly-160, Ser-240, His-280, Asp-242, and Asp-307. The structure and micro-environment of α-glucosidase enzymes were altered, which led to a decrease in α-glucosidase activity. This research identified that hypericin, an anthracene ketone compound, could be a novel α-glucosidase inhibitor and further applied to the development of potential anti-diabetic drugs.

Di-butyltin(iv) complexes with azo-carboxylates: synthesis, characterization, crystal structures and their anti-diabetic assay

The results of the anti-diabetic test of the compounds against the alpha glucosidase enzyme showed that2exhibits promising activity.

Inhibitory mechanism of two allosteric inhibitors, oleanolic acid and ursolic acid on α-glucosidase

Glycemic control which can be efficaciously regulated by inhibiting α-glucosidase activity is an effective therapy for diabetes mellitus. This work is to investigate the kinetics and inhibition mechanism of oleanolic acid and ursolic acid on α-glucosidase. Oleanolic acid and ursolic acid exhibited potent inhibitory activities with IC50 values of (6.35±0.02)×10-6 and (1.69±0.03)×10-5molL-1 respectively in a reversible and non-competitive manner. Both of them binding to α-glucosidase induced the conformational change and intrinsic fluorescence quenching of α-glucosidase. The binding constants of oleanolic acid and ursolic acid with α-glucosidase at 298K were (2.04±0.02)×103 and (1.87±0.02)×103Lmol-1, respectively. Docking results showed that oleanolic acid and ursolic acid bound in different allosteric sites of cavity 2 and cavity 4 on α-glucosidase, respectively, which triggered allosteric regulation to perturb conformational dynamics of α-glucosidase, eventually leading to a decrease of catalytic activity of the enzyme. The substrate was not catalyzed by α-glucosidase to generate further products due to formation of a nonreactive ternary complex of oleanolic acid- or ursolic acid-α-glucosidase-substrate. The combination of oleanolic acid and ursolic acid displayed a significant synergistic inhibition on α-glucosidase.

Maltase protein of Ogataea (Hansenula) polymorpha is a counterpart to the resurrected ancestor protein ancMALS of yeast maltases and isomaltases

Saccharomyces cerevisiae maltases use maltose, maltulose, turanose and maltotriose as substrates, isomaltases use isomaltose, α‐methylglucoside and palatinose and both use sucrose. These enzymes are hypothesized to have evolved from a promiscuous α‐glucosidase ancMALS through duplication and mutation of the genes. We studied substrate specificity of the maltase protein MAL1 from an earlier diverged yeast, Ogataea polymorpha (Op), in the light of this hypothesis. MAL1 has extended substrate specificity and its properties are strikingly similar to those of resurrected ancMALS. Moreover, amino acids considered to determine selective substrate binding are highly conserved between Op MAL1 and ancMALS. Op MAL1 represents an α‐glucosidase in which both maltase and isomaltase activities are well optimized in a single enzyme. Substitution of Thr200 (corresponds to Val216 in S. cerevisiae isomaltase IMA1) with Val in MAL1 drastically reduced the hydrolysis of maltose‐like substrates (α‐1,4‐glucosides), confirming the requirement of Thr at the respective position for this function. Differential scanning fluorimetry (DSF) of the catalytically inactive mutant Asp199Ala of MAL1 in the presence of its substrates and selected monosaccharides suggested that the substrate‐binding pocket of MAL1 has three subsites (–1, +1 and +2) and that binding is strongest at the –1 subsite. The DSF assay results were in good accordance with affinity (K_m) and inhibition (K_i) data of the enzyme for tested substrates, indicating the power of the method to predict substrate binding. Deletion of either the maltase (MAL1) or α‐glucoside permease (MAL2) gene in Op abolished the growth of yeast on MAL1 substrates, confirming the requirement of both proteins for usage of these sugars. © 2016 The Authors. Yeast published by John Wiley & Sons, Ltd.

Synthesis, characterization and anti-diabetic assay of diorganotin(iv) azo-carboxylates: crystal structure and topological studies of azo-dicarboxylic acid ligand and its cyclic tetranuclear dimethyltin(iv) complex

Two novel cyclic tetranuclear and a cyclic dimeric diorganotin(iv) azo-dicarboxylates have been reported. The complexes exhibited effective anti-diabetic activity.

A novel sucrose hydrolase from the bombycoid silkworms Bombyx mori, Trilocha varians, and Samia cynthia ricini with a substrate specificity for sucrose

Although membrane-associated sucrase activity has been detected in the midgut of various lepidopteran species, it has not yet been identified and characterized at the molecular level. In the present study, we identified a novel sucrose hydrolase (SUH) gene from the following three bombycoid silkworms: Bombyx mori, Trilocha varians, and Samia cynthia ricini and named them BmSuh, TvSuh, and ScSuh, respectively. The EST dataset showed that BmSuh is one of the major glycoside hydrolase genes in the larval midgut of B. mori. These genes were almost exclusively expressed in the larval midgut in all three species, mainly at the feeding stage. SUHs are classified into the glycoside hydrolase family 13 and show significant homology to insect maltases. Enzymatic assays revealed that recombinant SUHs were distinct from conventional maltases and exhibited substrate specificity for sucrose. The recombinant BmSUH was less sensitive to sugar-mimic alkaloids than TvSUH and ScSUH, which may explain the reason why the sucrase activity in the B. mori midgut was less affected by the sugar-mimic alkaloids derived from mulberry.

The specificity of α-glucosidase from Saccharomyces cerevisiae differs depending on the type of reaction: hydrolysis versus transglucosylation

Our investigation of the catalytic properties of Saccharomyces cerevisiae α-glucosidase (AGL) using hydroxybenzyl alcohol (HBA) isomers as transglucosylation substrates and their glucosides in hydrolytic reactions demonstrated interesting findings pertaining to the aglycon specificity of this important enzyme. AGL specificity increased from the para(p)- to the ortho(o)-HBA isomer in transglucosylation, whereas such AGL aglycon specificity was not seen in hydrolysis, thus indicating that the second step of the reaction (i.e., binding of the glucosyl acceptor) is rate-determining. To study the influence of substitution pattern on AGL kinetics, we compared AGL specificity, inferred from kinetic constants, for HBA isomers and other aglycon substrates. The demonstrated inhibitory effects of HBA isomers and their corresponding glucosides on AGL-catalyzed hydrolysis of p-nitrophenyl α-glucoside (PNPG) suggest that HBA glucosides act as competitive, whereas HBA isomers are noncompetitive, inhibitors. As such, we postulate that aromatic moieties cannot bind to an active site unless an enzyme-glucosyl complex has already formed, but they can interact with other regions of the enzyme molecule resulting in inhibition.

An Improved Neutral a-Glucosidase Assay for Assessment of Epididymal Function-Validation and Comparison to the WHO Method

Neutral α-glucosidase (NAG) activity in human seminal plasma is an important indicator for epididymis functionality. In the present study, the classic World Health Organization (WHO) method has been adapted to enhance assay robustness. Changes include modified enzyme reaction buffer composition and usage of an alternative enzyme inhibitor for background correction (glucose instead of castanospermine). Both methods have been tested in parallel on 144 semen samples, obtained from 94 patients/donors and 50 vasectomized men (negative control), respectively. Passing-Bablok regression analysis demonstrated equal assay performance. In terms of assay validation, analytical specificity, detection limit, measuring range, precision, and cut-off values have been calculated. These data confirm that the adapted method is a reliable, improved tool for NAG analysis in human semen.

Comparison of inhibitory activities and mechanisms of five mulberry plant bioactive components against α-glucosidase

The α-glucosidase inhibitory effects of five bioactive components, namely 1-deoxynojirimycin, cyanidin-3-glucoside, cyanidin-3-rutinoside, resveratrol and oxyresveratrol contained in mulberry (Morus, Moraceae) plants have been compared. Spectroscopy methods were employed to compare their α-glucosidase inhibitory mechanisms. The results revealed that 1-deoxynojirimycin (competitive), resveratrol and oxyresveratrol (noncompetitive) were stronger inhibitors than acarbose, while cyanidin-3-glucoside and cyanidin-3-rutinoside (mix competitive and noncompetitive) showed modest activities. 1-Deoxynojirimycin, resveratrol and oxyresveratrol could quench the fluorescence spectra statically by forming stable complexes, while the quenching of cyanidin-3-rutinoside and cyanidin-3-glucoside belonged to dynamic quenching by the collision of molecules. The interactions between ligands and α-glucosidase were mainly driven by hydrophobic force, or hydrogen bonding consequently induced conformational changes and reduced surface hydrophobicity. Docking results suggested that they could bind to α-glucosidase at different sites. This work provides useful information for the understanding of the ligands-α-glucosidase interactions and identifies oxyresveratrol as a potent α-glucosidase inhibitor.

Specificity of maltase to maltose in three different directions of reaction: hydrolytic, vanillyl alcohol glucoside and vanillyl alcohol isomaltoside synthesis

Vanillyl alcohol glucoside is very attractive molecule due to its very powerful physiological activity. In this article, a detailed kinetic study of transglucosylation of vanillyl alcohol was performed. It was demonstrated that this reaction is very efficient (selectivity factor is 149) and occurred by a ping-pong mechanism with inhibition by glucose acceptor. At low concentration of vanillyl alcohol one additional transglucosylation product was detected. Its structure was determined to be α-isomaltoside of vanillyl alcohol, indicating that vanillyl alcohol glucoside is a product of the first transglucosylation reaction and a substrate for second, so the whole reaction mechanism was proposed. It was demonstrated that the rate of isomaltoside synthesis is two orders of magnitude smaller than glucoside synthesis, and that maltase has interestingly high K(m) value to maltose when vanillyl alcohol glucoside is second transglucosylation substrate.

Berberine acutely inhibits the digestion of maltose in the intestine

ETHNOPHARMACOLOGICAL RELEVANCE

The Chinese Goldthread Rhizome has been used in the Traditional Chinese Medicine as an important ingredient of many formulas for the treatment of diabetes mellitus. Berberine, the main effective composition of Chinese Goldthread Rhizome, is also effective in treating diabetes in today's clinical practice of Traditional Chinese Medicine.

AIM OF THE STUDY

To evaluate the hypoglycemic activity of berberine which treats acutely on the postprandial blood glucose, and to explore the mechanism of this activity.

MATERIALS AND METHODS

1. One-dose preprandial intragastric administrations of berberine were given to normal animals (dogs and rats), and the postprandial blood glucose concentration curves were measured. Serum insulin enzyme linked immunosorbent assay (ELISA) was only performed in rats. 2. The euglycemic clamp test was performed to evaluate the effect of one-dose berberine intragastric administration on the blood glucose transformation and utilization rate in rats. 3. In the Caco-2 cell monolayer test, the changes of glucose concentration on the apical and basolateral sides were measured when the maltose solution containing berberine was added to the apical side. 4. The inhibition ratio of berberine against α-glucosidase was measured in vitro. 5. The effect of berberine on the fluorescence emission spectrums of α-glucosidase was studied.

RESULTS

One-dose preprandial intragastric administration of berberine delayed the rise of post-maltose blood glucose, did not affect postprandial blood glucose after glucose meal, and did not affect the insulin level in normal rats; reduced post-maltose blood glucose in normal dogs. 2. The result of euglycemic clamp test showed that one-dose intragastric administration of berberine had no effect on the blood glucose transformation and utilization rate in rats. 3. Berberine added to the maltose solution on the apical side of Caco-2 cell monolayer reduced the glucose concentration on the apical side. Glucose in basolateral side of all groups cannot be detected. 4. Berberine inhibited the activity of α-glucosidase in vitro. 5. Berberine significantly and concentration dependently quenched the fluorescence emission spectrum of α-glucosidase.

CONCLUSION

Our findings suggest an additional mechanism of the hypoglycemic activity of berberine by demonstrating its ability to acutely inhibit the α-glucosidase, and support the traditional use of berberine and Chinese Goldthread Rhizome for the treatment of diabetes mellitus.

Attachment ofMAL32-encoded maltase on the outside of yeast cells improves maltotriose utilization

The fermentation of maltotriose, the second most abundant fermentable sugar in wort, is often incomplete during high-gravity brewing. Poor maltotriose consumption is due to environmental stress conditions during high-gravity fermentation and especially to a low uptake of this sugar by some industrial strains. In this study we investigated whether the use of strains with an alpha-glucosidase attached to the outside of the cell might be a possible way to reduce residual maltotriose. To this end, the N-terminal leader sequence of Kre1 and the carboxy-terminal anchoring domain of either Cwp2 or Flo1 were used to target maltase encoded by MAL32 to the cell surface. We showed that Mal32 displayed on the cell surface of Saccharomyces cerevisiae laboratory strains was capable of hydrolysis of alpha-1,4-linkages, and that it increased the ability of a strain lacking a functional maltose permease to grow on maltotriose. Moreover, the enzyme was also expressed and found to be active in an industrial strain. These data show that expressing a suitable maltase on the cell surface might provide a means of modifying yeast for more complete maltotriose utilization in brewing and other fermentation applications.

Solvent isotope effects on alpha-glucosidase

The solvent kinetic isotope effects (SKIE) on the yeast alpha-glucosidase-catalyzed hydrolysis of p-nitrophenyl and methyl-d-glucopyranoside were measured at 25 degrees C. With p-nitrophenyl-D-glucopyranoside (pNPG), the dependence of k(cat)/K(m) on pH (pD) revealed an unusually large (for glycohydrolases) solvent isotope effect on the pL-independent second-order rate constant, (DOD)(k(cat)/K(m)), of 1.9 (+/-0.3). The two pK(a)s characterizing the pH profile were increased in D(2)O. The shift in pK(a2) of 0.6 units is typical of acids of comparable acidity (pK(a)=6.5), but the increase in pK(a1) (=5.7) of 0.1 unit in going from H(2)O to D(2)O is unusually small. The initial velocities show substrate inhibition (K(is)/K(m) approximately 200) with a small solvent isotope effect on the inhibition constant [(DOD)K(is)=1.1 (+/-0.2)]. The solvent equilibrium isotope effects on the K(is) for the competitive inhibitors D-glucose and alpha-methyl D-glucoside are somewhat higher [(DOD)K(i)=1.5 (+/-0.1)]. Methyl glucoside is much less reactive than pNPG, with k(cat) 230 times lower and k(cat)/K(m) 5 x 10(4) times lower. The solvent isotope effect on k(cat) for this substrate [=1.11 (+/-0. 02)] is lower than that for pNPG [=1.67 (+/-0.07)], consistent with more extensive proton transfer in the transition state for the deglucosylation step than for the glucosylation step.