Galactosidases

Anti-Pathogenic Functions of Non-Digestible Oligosaccharides In Vitro

Non-digestible oligosaccharides (NDOs), complex carbohydrates that resist hydrolysis by salivary and intestinal digestive enzymes, fulfill a diversity of important biological roles. A lot of NDOs are known for their prebiotic properties by stimulating beneficial bacteria in the intestinal microbiota. Human milk oligosaccharides (HMOs) represent the first prebiotics that humans encounter in life. Inspired by these HMO structures, chemically-produced NDO structures (e.g., galacto-oligosaccharides and chito-oligosaccharides) have been recognized as valuable food additives and exert promising health effects. Besides their apparent ability to stimulate beneficial microbial species, oligosaccharides have shown to be important inhibitors of the development of pathogenic infections. Depending on the type and structural characteristics, oligosaccharides can exert a number of anti-pathogenic effects. The most described effect is their ability to act as a decoy receptor, thereby inhibiting adhesion of pathogens. Other ways of pathogenic inhibition, such as interference with pathogenic cell membrane and biofilm integrity and DNA transcription, are less investigated, but could be equally impactful. In this review, a comprehensive overview of In vitro anti-pathogenic properties of different NDOs and associated pathways are discussed. A framework is created categorizing all anti-pathogenic effects and providing insight into structural necessities for an oligosaccharide to exert one of these effects.

Enzyme adsorption-induced activity changes: a quantitative study on TiO2 model agglomerates

Background

Activity retention upon enzyme adsorption on inorganic nanostructures depends on different system parameters such as structure and composition of the support, composition of the medium as well as enzyme loading. Qualitative and quantitative characterization work, which aims at an elucidation of the microscopic details governing enzymatic activity, requires well-defined model systems.

Results

Vapor phase-grown and thermally processed anatase TiO₂ nanoparticle powders were transformed into aqueous particle dispersions and characterized by dynamic light scattering and laser Doppler electrophoresis. Addition of β-galactosidase (β-gal) to these dispersions leads to complete enzyme adsorption and the generation of β-gal/TiO₂ heteroaggregates. For low enzyme loadings (~4% of the theoretical monolayer coverage) we observed a dramatic activity loss in enzymatic activity by a factor of 60–100 in comparison to that of the free enzyme in solution. Parallel ATR-IR-spectroscopic characterization of β-gal/TiO₂ heteroaggregates reveals an adsorption-induced decrease of the β-sheet content and the formation of random structures leading to the deterioration of the active site.

Conclusions

The study underlines that robust qualitative and quantitative statements about enzyme adsorption and activity retention require the use of model systems such as anatase TiO₂ nanoparticle agglomerates featuring well-defined structural and compositional properties.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-017-0283-4) contains supplementary material, which is available to authorized users.

Functional metagenomics reveals novel β-galactosidases not predictable from gene sequences

The techniques of metagenomics have allowed researchers to access the genomic potential of uncultivated microbes, but there remain significant barriers to determination of gene function based on DNA sequence alone. Functional metagenomics, in which DNA is cloned and expressed in surrogate hosts, can overcome these barriers, and make important contributions to the discovery of novel enzymes. In this study, a soil metagenomic library carried in an IncP cosmid was used for functional complementation for β-galactosidase activity in both Sinorhizobium meliloti (α-Proteobacteria) and Escherichia coli (γ-Proteobacteria) backgrounds. One β-galactosidase, encoded by six overlapping clones that were selected in both hosts, was identified as a member of glycoside hydrolase family 2. We could not identify ORFs obviously encoding possible β-galactosidases in 19 other sequenced clones that were only able to complement S. meliloti. Based on low sequence identity to other known glycoside hydrolases, yet not β-galactosidases, three of these ORFs were examined further. Biochemical analysis confirmed that all three encoded β-galactosidase activity. Lac36W_ORF11 and Lac161_ORF7 had conserved domains, but lacked similarities to known glycoside hydrolases. Lac161_ORF10 had neither conserved domains nor similarity to known glycoside hydrolases. Bioinformatic and structural modeling implied that Lac161_ORF10 protein represented a novel enzyme family with a five-bladed propeller glycoside hydrolase domain. By discovering founding members of three novel β-galactosidase families, we have reinforced the value of functional metagenomics for isolating novel genes that could not have been predicted from DNA sequence analysis alone.

Environmental Topology and Water Availability Modulates the Catalytic Activity of β-Galactosidase Entrapped in a Nanosporous Silicate Matrix

In the present work we studied the catalytic activity of E. coli β-Gal confined in a nanoporous silicate matrix (E_β-Gal) at different times after the beginning of the sol-gel polymerization process. Enzyme kinetic experiments with two substrates (ONPG and PNPG) that differed in the rate-limiting steps of the reaction mechanism for their β-Gal-catalyzed hydrolysis, measurements of transverse relaxation times (T₂) of water protons through ¹H-NMR, and scanning electron microscopy analysis of the gel nanostructure, were performed. In conjunction, results provided evidence that water availability is crucial for the modulation observed in the catalytic activity of β-Gal as long as water participate in the rate limiting step of the reaction (only with ONPG). In this case, a biphasic rate vs. substrate concentration was obtained exhibiting one phase with catalytic rate constant (k_cA), similar to that observed in solution, and another phase with a higher and aging-dependent catalytic rate constant (k_cB). More structured water populations (lower T₂) correlates with higher catalytic rate constants (k_cB). The T₂-k_cB negative correlation observed along the aging of gels within the 15-days period assayed reinforces the coupling between water structure and the hydrolysis catalysis inside gels.

Formation of oligosaccharides during enzymatic lactose: Part I: State of art

Enzymatic lactose hydrolysis by beta-galactosidase (lactase) was investigated with respect to the formation of oligosaccharides. An analysis of the formation of oligosaccharides and their control is important in the development of technical applications for enzymatic lactose hydrolysis. The available literature data on transfer reactions of lactase were reviewed, compared, and presented in a concise tabular form. Mechanisms and possible ways of modelling enzymatic lactose hydrolysis, including formation of oligosaccharides, are presented.

Influence of water activity in the synthesis of galactooligosaccharides produced by a hyperthermophilic β-glycosidase in an organic medium

The present study evaluated the influence of water activity and lactose concentration on the synthesis of galactooligosaccharides (GOS), by means of a hyperthermophilic beta-glycosidase in an organic system. The production of GOS gradually grew as water activity increased in the reaction system; later, their synthesis decreased as water activity increased. The authors used the response surface methodology to study how different water activities and different concentrations of lactose influenced the synthesis of GOS and their length. In every case, the variable that proved to have the greatest effect on GOS synthesis was water activity. Maximum GOS3 synthesis was reached at a water activity interval of 0.44-0.57, with lactose concentrations of 0.06%-0.1%, while GOS4 and GOS5 maxima were reached at water activity intervals of 0.47-0.57 and 0.49-0.60, respectively. The research showed that higher water activity was required to synthesize GOS of greater length. Synthesis of GOS would then depend on the flexibility of the enzyme, which in turn would depend on water activity of the reaction system. This hypothesis was supported by experiments in which the reaction temperature was modified in order to change the flexibility of the enzyme, thus leading to longer GOS.

Thiooligosaccharides as tools for structural biology

Oligosaccharides in which at least one glycosidic oxygen atom is replaced with a sulfur atom can be routinely synthesized and act as competitive inhibitors of various glycoside hydrolases. Recent studies using both X-ray crystallography and other biophysical techniques provide structural insight into binding, recognition, and the catalytic mechanism of action of these enzymes.

Hydrolase and sialyltransferase activities of trypanosoma cruzi trans-sialidase towards NeuAc-alpha-2,3-gal-Gal-beta-O-PNP

NeuAc-alpha-2,3-Gal-beta-O-PNP has been synthesised and its ability to act as a substrate for the hydrolase and transferase activities of Trypanosoma cruzi trans-sialidase have been investigated. The turn-over of this compound shows marked differences from the behaviour of NeuAc-MU. In addition, distinct differences in the action of T. cruzi trans-sialidase and Clostridium perfringens neuraminidase on NeuAc-alpha-2,3-Gal-beta-O-PNP were apparent.

Effect of beta-galactosidase hydration on alcoholysis reaction in organic one-phase liquid systems

Alcoholysis reactions were performed in organic one-phase liquid systems with E. coli beta-galactosidase to produce heptyl-beta-galactoside from lactose and 1-heptanol. The reaction rate was highly dependent on the amount of water solubilized in the alcohol. A larger amount of water led to a system of two liquid phases in which the alcoholysis rate was 73% faster than in the one-phase system. No hydrolysis reaction of either lactose or product was observed in one-phase liquid systems up to 20 h, independent of the water content. Solubility of lactose in the organic phase increased with the water content in the system and the reaction followed the Michaelis-Menten model. Water activity was calculated for heptanol containing different amounts of water and the obtained values were used to estimate the hydration of beta-galactosidase from known models. Enzyme activity correlated with sorbed water, similar to the behavior reported for lysozyme in low water environments. It is concluded that water contribution to enzyme hydration dominates the rate of reaction compared to its effect on lactose solubilization.

Alcoholysis and reverse hydrolysis reactions in organic one-phase system with a hyperthermophilic beta-glycosidase

Alcoholysis and reverse hydrolysis reactions were performed enzymatically in one-phase water-saturated 1-heptanol systems. Lactose or glucose was used as substrate to produce heptyl-beta-galactoside and/or heptyl-beta-glucoside, respectively. When alcoholysis of lactose was performed at 37 degrees C with beta-galactosidase from Escherichia coli, the initial rate was 14 nmol/mL min, and the limiting factors were the poor solubility of the substrate in 1-heptanol and low thermal stability of the enzyme. When a hyperthermophilic beta-glycosidase was used at 90 degrees C, the rate was 3.14-fold higher; in this case a higher concentration of soluble lactose in the water-saturated heptanol was available to the enzyme due to the higher temperature. The hyperthermophilic beta-glycosidase was also able to use glucose and galactose as substrates to achieve the reverse hydrolysis reaction. As a consequence, when lactose was used as substrate, heptyl-beta-galactoside was formed by alcoholysis, while the released glucose moiety was used in a secondary reverse hydrolysis reaction to produce heptyl-beta-glucoside. Both reactions followed Michaelis-Menten kinetics behavior. Neither lactose nor heptyl glycosides were hydrolyzed by this enzyme in water-saturated heptanol. However, the conversion was limited by a strong product inhibition and the formation of oligosaccharides, especially at high substrate concentrations, reducing the final glycoside yield.

Separation and characterization of four enzyme forms of beta-galactosidase from Saccharomyces lactis

beta-Galactosidase from Saccharomyces lactis has been purified to serve as a model for the kinetic behavior of human lactase in adult lactase deficiency. Enzymes from both species are neutral and follow Michaelis-Menten kinetics. beta-Galactosidase of S. lactis is more readily available than the human lactase. An enzyme preparation from S. lactis (Maxilact 40,000), which is used commercially to hydrolyze lactose in milk, has been found to contain four isozymes of beta-galactosidase. Methods have been developed for the separation and purification of each of the four enzymes. The enzymes were found to differ in molecular mass, kinetic behavior, isoelectric point, response to pH, specific volume and sensitivity to metal ions. The four enzymes had apparent molecular masses of 630 kDa, 550 kDa, 41 kDa and 19 kDa. Their specificity constants (kcat/Km) were found to be 42.0, 355.2, 0.38 and 0.48 mM-1 s-1, respectively. The techniques of reiterated ultrafiltration used for the isolation of these isozymes may be applicable to other purification processes.

[The effect of a raffinose diet and cooked legumes on various processes in the large bowel in the rat]

Changes of pH, enzyme activity and microflora in the large bowel of the rat after feeding them various diets containing raffinose and leguminous seeds (soybean, peas and beans) have been studied. Feeding a 12% raffinose-containing diet as well as cooked leguminous seeds lowered pH. However, similar decrease of pH was observed after some other diets (for example, milk powder or raw pearl barley). Remarkable alpha-galactosidase activity in the large bowel of rats after legume diet has been observed whereas it was not noted in the small bowel. The source of alpha-galactosidase are probably bacteria of the large intestine content (Lactobacillus spp., Enterococcus, Escherichia coli). No relationship between the isolated microflora and kind of a diet was observed.

Conformations in solution of alpha,alpha-trehalose, alpha-D-glucopyranosyl alpha-D-mannopyranoside, and their 1-thioglycosyl analogs, and a tentative correlation of their behaviour with respect to the enzyme trehalase

The conformation in solution of alpha-D-glucopyranosyl alpha-D-glucopyranoside (alpha,alpha-trehalose, 1), alpha-D-glucopyranosyl alpha-D-mannopyranoside (3) and their corresponding 1-thioglycosyl analogs, alpha-D-glucopyranosyl 1-thio-alpha-D-glucopyranoside (1-thio-alpha,alpha-trehalose, 2) and alpha-D-glucopyranosyl 1-thio-alpha-D-mannopyranoside (4) were established from high-resolution 1H-NMR and 13C-NMR measurements. These experimental results are in good agreement with the conformations as inferred from hard-sphere calculations. The dihedral angles phi H and psi H are not significantly different for the O-glycosyl disaccharides 1 and 3 compared with their 1-thioglycosyl analogs 2 and 4; however, the internuclear H-1--H-1' and H-1--H-5' distances appear to be longer for 1-thiodisaccharides. This may account for the differences in affinities of cockchafer trehalase which have been observed. This enzyme exhibits less affinity for the competitive inhibitor alpha-D-glucopyranosyl 1-thio-alpha-D-mannopyranoside (4) than for its O-glycosyl analog 3 (Ki 0.055 mM versus 0.0057 mM). From the similarity in Ki between 1-thio-alpha, alpha-trehalose and alpha-D-glucopyranosyl 1-thio-alpha-D-mannopyranoside (0.050 mM versus 0.055 mM), it is possible to assume a similar decrease in the enzymic affinity between the natural substrate (1) and the corresponding 1-thioglycosyl inhibitor (2), which can together be ascribed to the aforementioned difference in the conformation of the molecules.

[Excretion of carbohydrates by rats fed legume seeds]

A study of sugars excretion in rats after feeding with diets containing various raffinose content (0, 4, 8 and 12%) and cooked leguminous seeds (soybean, peas and beans) has been performed. It was noted, that feeding with raffinose-containing diet has no effect on sugars level in urine during 10 days of experiment. Feeding with the diets containing 8 and 12% raffinose caused highly increased excretion of this sugar and its metabolites in faeces after first 24 h. After next few days of experiment in despite of high raffinose content in diets the level of raffinose excretion in the faeces came back to the initial one. In the case of leguminous seeds feeding of rats increased excretion of sugars in faeces was observed also after 20-24 h, and was maintained on the same level during 10 days of experiment. The ratio of excreted to consumed sugars was limited to 2-5% only. It is presumed that there were stachyose and verbascose metabolites, previously identified in leguminous seeds.

The beta-glucosidase from Botryodiplodia theobromae. Mechanism of enzyme action

1. In the presence of a high concentration of p-nitrophenyl beta-D-glucopyranoside (donor) the rates of production of p-nitrophenol and a transglucosylation product (1-glyceryl beta-D-glucopyranoside) increased, whereas the rate of production of glucose decreased with increasing concentration of glycerol in reactions catalysed by the high-molecular-weight beta-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) obtained from culture filtrates of Botryodiplodia theobromae Pat. 2. When [donor] greater than Km the rate of production of p-nitrophenol was higher in the presence of glycerol than in its absence, whereas when [donor] less than Km the rate of production of p-nitrophenol was lower in the presence of glycerol than in its absence. 3. Glycerol increased both the Michaelis constant (Km) and maximum velocity (Vmax.), whereas dioxan increased Km but decreased Vmax. 4. Up to 1 mM-AgNO3 had no effect on enzyme activity. 5. A 2H-solvent-isotope-effect [Vmax. (H2O)/V max. (2H2O)] value of 1.40 +/- 0.05 was found at pH (or p2H) 5.8 6. alpha-2H-kinetic isotope-effect (kappa H/kappa 2H) values of 1.03 +/- 0.01 and 1.05 +/- 0.01 were found in the absence and presence of glycerol respectively. 7. Although maltose was a non-competitive inhibitor of beta-glucosidase activity, the ratio of velocity in the presence of glycerol to that in its absence increased, after an initial decline, with increasing concentration of maltose. 8. These results are discussed in terms of a mechanism involving a solvent-separated glucosyl cation-carboxylate ion-pair, which has greater affinity for alcoholic glucosyl acceptors, and an intimate ion-pair, which has greater affinity for water as a glucosyl acceptor and which could collapse reversibly and rapidly into a preponderance of an unreactive covalent glucosyl-enzyme.

Lag in adaptation to lactose as a probe to the timing of permease incorporation into the cell membrane

If bacteria are incapable of forming and incorporating proteins into the cytoplasmic membranes in all phases of the cell cycle, then not all cells from an asynchronous culture should be capable of growth when switched to a new carbon and energy source whose metabolism requires new membrane function. The transfer of an inducible culture to low lactose provides such a situation since the cells cannot grow unless galactoside permease can function to concentrate the lactose internally. From such experiments, it was concluded that the Y gene product of the lac operon is synthesized, incorporated, and can start functioning in active transport, at any time throughout the bulk of the cell cycle. Not only were the lags before growth re-ensued much shorter than would be expected if the membrane transport capability could only be developed in a small portion of the cycle, but brief pulses of a gratuitous inducer shortened the lags much further. Three types of Escherichia coli ML 30 culture were studied: cells that had exhausted the limiting glucose; cells taken directly from glucose-limited chemostats; and a washed suspension of highly catabolite repressed cells from cultures grown in high levels of glucose and gluconate. The growth studies reported here were performed on-line with a minicomputer. They represent at least an order of magnitude increase in accuracy in estimating growth parameters over previous instrumentation.

The beta-galactosidase-catalysed hydrolyses of beta-d-galactopyranosyl pyridium salts. Rate-limiting generation of an enzyme-bound galactopyranosyl cation in a process dependent only on aglycone acidity

1. beta-d-Galactopyranosyl pyridinium salts are well-behaved substrates for the beta-galactosidase of Escherichia coli, catalysis occurring by the interaction of the salt itself with the normal active site of the protein. 2. logk(cat.) values for seven such salts show a linear relationship (correlation coefficient=-0.997) with the pK(a) of the parent pyridine. 3. The beta-d-galactopyranosyl derivatives of pyridine and 4-bromoisoquinoline exhibit alpha-deuterium kinetic isotope effects of 1.136+/-0.040 and 1.187+/-0.046 on their enzymic hydrolysis, indicating formation of a galactopyranosyl cation in the rate-limiting step. 4. This behaviour of the pyridinium salts contrasts with the behaviour of aryl galactosides and this contrast can be accommodated by the beta-galactosidase mechanism of Sinnott & Souchard (1973). 5. The alpha-deuterium kinetic isotope effect for the hydrolysis of beta-d-galactopyranosyl azide is 1.098+/-0.033; comparison of the k(cat.) value of the azide with that of a pyridinium salt of the same aglycone pK(a) enables a maximum factor of 70 to be ascribed to the acceleration of the departure of azide by intracomplex general acid catalysis. 6. The possibility of the rate-limiting process in the glycosidase-catalysed hydrolysis of aryl glycosides being a conformation change is considered for a number of glycosidases where correlations of k(cat.) with aglycone acidity, reported in the literature, have been unsuccessful.

Alpha-glactosidase activity of lactobacilli

alpha-Galactosidase (EC 3.2.1.22) activity was observed in cell-free extracts of Lactobacillus fermenti, L. brevis, L. buchneri, L. cellobiosis, and L. salivarius subsp. salivarius. The cultural conditions under which the enzyme activity was detected suggest that the enzyme is constitutive and present in the soluble fraction in the cell. The enzyme preparations readily hydrolyzed melibiose and other oligosaccharides containing alpha(1 --> 6) linked galactose. Although the cell-free extracts of L. fermenti and L. brevis are negative for beta-fructofuranosidase (EC 3.2.1.26), they hydrolyzed melibiose, stachyose, and raffinose in decreasing order of activity. The beta-fructofuranosidase-positive L. buchneri, L. cellobiosis, and L. salivarius preparations hydrolyzed melibiose, raffinose, and stachyose in decreasing rates of activity. The alpha-galactosidases from different lactobacilli showed optimum activity in pH range 5.2 to 5.9. L. fermenti and L. salivarius preparations exhibited maximum activity between 40 to 44 C and 48 to 51 C, respectively, whereas a 38 to 42 C range was observed for other lactobacilli. Cell-free extract of L. cellobiosis was studied for transgalactosylase activity. When incubated with melibiose, a new compound was detected and tentatively identified as manninotriose.

The effect of methanol and dioxan on the rates of the beta-galactosidase-catalysed hydrolyses of some beta-D-galactrophyranosides: rate-limiting degalactosylation. The ph-dependence of galactosylation and degalactosylation

1. The effect of methanol on the beta-galactosidase-catalysed hydrolysis of some nitrophenyl beta-d-galactopyranosides has been studied under steady-state conditions. 2. The initial fractional rate of increase of k(cat.) as a function of methanol concentration with 2,4- and 3,5-dinitrophenyl beta-d-galactopyranosides, but not with the other substrates studied, indicated that degalactosylation of the enzyme was rate-limiting. 3. The decrease in k(cat.) at high methanol concentrations for these substrates is considered to arise from causes other than galactosylation becoming rate-limiting. 4. Both galactosylation and degalactosylation of the enzyme require protonation of a group of pK(a) approx. 9.

The role of magnesium ions in beta-galactosidase hydrolyses. Studies on charge and shape of the beta-galactopyranosyl binding site

1. beta-d-Galactopyranosyl trimethylammonium bromide is a competitive inhibitor of beta-galactosidase, K(i)=1.4+/-0.2mm at 25 degrees C. 2. Tetramethylammonium bromide is not an inhibitor (K(i)>0.2m). 3. The kinetics of deactivation of Mg(2+)-saturated, and of inhibitor-and Mg(2+)-saturated, enzyme in 10mm-EDTA are similar. 4. The apparent K(i) for the glycosylammonium salt is approx. 2.2mm in the absence of Mg(2+). 5. It is therefore concluded that Mg(2+) and the inhibitor bind independently, and that the Mg(2+) does not act as an electrophilic catalyst. 6. Complexant fluorescence measurements indicate binding of 1 Mg(2+) ion per 135000-dalton protomer. 7. This stoicheiometry is confirmed by equilibrium dialysis. 8. 1,6-Anhydrogalactopyranose is neither a substrate (k(cat.)/K(m)< 3x10(-2)m(-1).S(-1)) nor an inhibitor (K(i)>0.2m). 9. Considerations of conformations available to the cationic inhibitor and to the anhydrogalactose indicate that the substrate is bound with the pyranose ring in a conformation not greatly different from the normal chair (C1) conformation.