Kinetic Modeling of Lactose Hydrolysis by a β-Galactosidase from Kluyveromices Fragilis

Galacto-Oligosaccharide (GOS) Synthesis during Enzymatic Lactose-Free Milk Production: State of the Art and Emerging Opportunities

Much attention has recently been paid to β-Galactosidases (β-D-galactoside galactohidrolase; EC 3.2.1.23), commonly known as lactases, due to the lactose intolerance of the human population and the importance of dairy products in the human diet. This enzyme, produced by microorganisms, is being used in the dairy industry for hydrolyzing the lactose found in milk to produce lactose-free milk (LFM). Conventionally, β-galactosidases catalyze the hydrolysis of lactose to produce glucose and galactose in LFM; however, they can also catalyze transgalactosylation reactions that produce a wide range of galactooligosaccharides (GOS), which are functional prebiotic molecules that confer health benefits to human health. In this field, different works aims to identify novel microbial sources of β-galactosidase for removing lactose from milk with the relative GOS production. Lactase extracted from thermophilic microorganisms seems to be more suitable for the transgalactosylation process at relatively high temperatures, as it inhibits microbial contamination. Different immobilization methods, such as adsorption, covalent attachment, chemical aggregation, entrapment and micro-encapsulation, have been used to synthesize lactose-derived oligosaccharides with immobilized β-galactosidases. In this mini-review, particular emphasis has been given to the immobilization techniques and bioreactor configurations developed for GOS synthesis in milk, in order to provide a more detailed overview of the biocatalytic production of milk oligosaccharides at industrial level.

Enzyme-catalyzed cascade reactions on multienzyme proteinosomes

In this research, to mimic the structures and the functionalities of the organelles in living cells multienzyme proteinosomes with β-galactosidase (β-gal), glucose oxidase (GOx) and horseradish peroxidase (HRP) on the surfaces are fabricated by hydrophobic-interaction induced self-assembly approach. To investigate the mechanism of the formation of proteinosomes, poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) and bovine serum albumin are employed in a model system and the study demonstrates that the hydrophobic interaction between the dehydrated polymer chains and the hydrophobic patches on the proteins plays a key role in the fabrication of the proteinosomes. Based on the model system, multienzyme proteinosomes with β-gal, GOx and HRP on the surfaces are fabricated through hydrophobic interaction between PDEGMA and enzyme molecules. Enzyme-catalyzed cascade reactions are performed on the surfaces of the proteinosomes, and the immobilized enzymes show higher bioactivities than the "free" enzymes, due to the direct transfer of the product as a substrate from one enzyme molecule to another. This research provides a unique method for the synthesis of multienzyme proteinosomes with improved bioactivities, and the biofunctional structures will find promising applications in medical and biological science.

Cloning, expression, and bioinformatics analysis and characterization of a β-galactosidase from Bacillus coagulans T242

The activities of β-galactosidases from bacteria and molds are affected by temperature, pH, and other factors in the processing of dairy products, limiting their application, so it is necessary to find alternative lactases. In this study, the β-galactosidase gene from Bacillus coagulans T242 was cloned, co-expressed with a molecular chaperone in Escherichia coli BL21, and subjected to bioinformatic and kinetic analyses and lactase characterization. The results show that the enzyme is a novel thermostable neutral lactase with optimum hydrolytic activity at pH 6.8 and 50°C. The thermal stability and increased lactose hydrolysis activity of β-galactosidase in the presence of Ca²⁺ indicated its potential application in the dairy industry.

Effective detection of biocatalysts with specified activity by using a hydrogel-based colourimetric assay - β-galactosidase case study

The main aim of this study was to prepare gelatine-based hydrogels containing entrapped substrate and to examine the applicability of these matrices for detection of enzymes with a specified catalytic activity. The general research concept assumed the use of a substrate that, in the presence of a particular enzyme, will quickly undergo conversion to a coloured product. ortho-Nitrophenyl-β-D-galactopyranoside (ONPG) was used as the immobilized substrate and β-galactosidase from Kluyveromyces lactis as the biocatalyst to be determined. Among other factors, the range of detectable concentrations of galactosidase, the operational pH range, the time necessary to achieve a visible response and the preferred storage conditions for the test were determined. As a result, an effective colourimetric test for β-galactosidase detection was obtained. Its main advantages include (i) the effective detection of the enzyme at concentrations greater than or equal to 0.6 mg.L-1, (ii) the ability to perform initial quantification of the enzyme on the basis of the intensity of the obtained colour (iii) applicability in a wide pH range (from 4.0 to 9.0), (iv) a relatively short response time (from 1 to a maximum of 30 minutes) and (v) stability in long-term storage at 4°C (90 days without loss of specific properties).

Optimization of nutritional components of medium by response surface methodology for enhanced production of lactase

Lactase has excellent applications in dairy industry and commercially this enzyme is produced from bacterial sources but not in high yields. In this work, the production of lactase was improved by designing of nutrient components in fermentation medium by one factor at a time. Lactose and yeast extract were selected as preferable carbon and nitrogen sources for lactase production with tryptophan and MgSO4 showing enhanced production. Statistical analysis proved to be a useful and powerful tool in developing optimum fermentation conditions. The individual and interactive role of lactose, yeast extract, magnesium sulfate, and tryptophan concentration on lactase production was examined by central composite design. Submerged fermentation with Bacillus subtilis strain VUVD001 produced lactase activity of 63.54 U/ml in optimized medium. The activity was threefold higher in comparison to an unoptimized medium. This result confirmed that the designed medium was useful for producing higher yields of lactase.

Ultrasonic Monitoring of Enzyme Catalysis; Enzyme Activity in Formulations for Lactose-Intolerant Infants

The paper introduces ultrasonic technology for real-time, nondestructive, precision monitoring of enzyme-catalyzed reactions in solutions and in complex opaque media. The capabilities of the technology are examined in a comprehensive analysis of the effects of a variety of diverse factors on the performance of enzyme β-galactosidase in formulations for reduction of levels of lactose in infant milks. These formulations are added to infant's milk bottles prior to feeding to overcome the frequently observed intolerance to lactose (a milk sugar), a serious issue in healthy development of infants. The results highlight important impediments in the development of these formulations and also illustrate the capability of the described ultrasonic tools in the assessment of the performance of enzymes in complex reaction media and in various environmental conditions.

Investigation of Film with β-Galactosidase Designed for Stabilization and Handling in Dry Configuration

Gelatin-based films with an immobilized enzyme designed for extending the stability of the protein in dry, non-powder configuration with precise dosing attributes were subjected to stress conditions of temperature and relative humidity. β-galactosidase was used as model functional protein. The film configuration preserved the activity of the enzyme under the different storage conditions investigated, which include room temperature under low (ambient) and high (75%) relative humidity, and 36 °C under low (oven) and high relative humidity conditions for a period of 46 days. The influence of the enzyme and plasticizer (glycerol) on the physical and mechanical properties of the films was investigated using DMA (dynamic mechanical analysis). Films containing 5% β-galactosisdase and glycerol concentrations of 14% or greater exhibited greater tensile strength, Young's modulus, and elongation at break than films with equal concentrations of plasticizer but devoid of any enzyme. The surface texture of the films was analyzed using scanning electron microscopy (SEM). β-galactosidase and glycerol have opposite effects on the surface morphology of the films. Increasing concentrations of the enzyme result in rougher film surface, whereas increasing the concentration of glycerol leads to films with denser and smoother surface. The results obtained suggest that the dry film configuration approach can help in facilitating the stabilization, handling, storage, and transportation of functional proteins in a cost effective manner.

Characterization of Sulfolobus solfataricus β-galactosidase mutant F441Y expressed in Pichia pastoris

BACKGROUND

β-Galactosidases are used to synthesize galactooligosaccharides (GOS). Since thermostable β-galactosidases have the advantages of high optimal temperature, thermostability as well as prevention of bacterial contamination in the production of GOS, they have received more attention in research. In this study a mutant of Sulfolobus solfataricus β-galactosidase, F441Y, was expressed in Pichia pastoris KM71.

RESULTS

The activity of the recombinant enzyme reached 204.9 U mL⁻¹ after induction by methanol in a 3 L bioreactor for 80 h. Purification using ion exchange and hydrophobic interaction chromatographies resulted in a substantially pure recombinant β-galactosidase that migrated with an apparent molecular weight of 56 kDa in an SDS-PAGE gel. The enzymatic properties were measured and the optimal pH was 5 and the optimal temperature was 85 °C. Using lactose as substrate, the K(m) and k(cat) values were found to be 26.3 mmol L⁻¹ and 160.1 min⁻¹ respectively. After optimizing the reaction conditions for GOS production, the yield of GOS produced by the recombinant enzyme at pH 6 and 75 °C with 700 g L⁻¹ lactose solution and an enzyme quantity of 9 U mL⁻¹ reached 61%.

CONCLUSION

The F441Y of β-galactosidase expressed in P. pastoris KM71 has potential application in the industrial preparation of GOS.

Purification and properties of a β-galactosidase with potential application as a digestive supplement

Functional-based screening of crude beta-galactosidase activities from 42 yeast strains resulted in the selection of a single enzyme of potential interest as a digestive supplement. beta-Galactosidase produced by Kluyveromyces marxianus DSM5418 was purified to homogeneity by a combination of gel filtration, ion-exchange, and hydroxylapatite chromatographies. The denatured (123 kDa) and native molecular masses (251 kDa) suggest that the enzyme is a homodimer. The optimum pH and temperature of the purified enzyme were 6.8 and 37 degrees C, respectively. The unpurified beta-galactosidase in particular displayed a high level of stability when exposed to simulated intestinal conditions in vitro for 4 h. Matrix-assisted laser desorption ionization mass sectrometry analysis revealed that the enzyme's trypsin-generated peptide mass fingerprint shares several peptide fragment hits with beta-galactosidases from Kluyveromyces lactis. This confirms the enzyme's identity and indicates that significant sequence homology exists between these enzymes.

Secretion and properties of a hybrid Kluyveromyces lactis-Aspergillus niger beta-galactosidase

BACKGROUND

The beta-galactosidase from Kluyveromyces lactis is a protein of outstanding biotechnological interest in the food industry and milk whey reutilization. However, due to its intracellular nature, its industrial production is limited by the high cost associated to extraction and downstream processing. The yeast-system is an attractive method for producing many heterologous proteins. The addition of a secretory signal in the recombinant protein is the method of choice to sort it out of the cell, although biotechnological success is not guaranteed. The cell wall acting as a molecular sieve to large molecules, culture conditions and structural determinants present in the protein, all have a decisive role in the overall process. Protein engineering, combining domains of related proteins, is an alternative to take into account when the task is difficult. In this work, we have constructed and analyzed two hybrid proteins from the beta-galactosidase of K. lactis, intracellular, and its Aspergillus niger homologue that is extracellular. In both, a heterologous signal peptide for secretion was also included at the N-terminus of the recombinant proteins. One of the hybrid proteins obtained has interesting properties for its biotechnological utilization.

RESULTS

The highest levels of intracellular and extracellular beta-galactosidase were obtained when the segment corresponding to the five domain of K. lactis beta-galactosidase was replaced by the corresponding five domain of the A. niger beta-galactosidase. Taking into account that this replacement may affect other parameters related to the activity or the stability of the hybrid protein, a thoroughly study was performed. Both pH (6.5) and temperature (40 degrees C) for optimum activity differ from values obtained with the native proteins. The stability was higher than the corresponding to the beta-galactosidase of K. lactis and, unlike this, the activity of the hybrid protein was increased by the presence of Ni2+. The affinity for synthetic (ONPG) or natural (lactose) substrates was higher in the hybrid than in the native K. lactis beta-galactosidase. Finally, a structural-model of the hybrid protein was obtained by homology modelling and the experimentally determined properties of the protein were discussed in relation to it.

CONCLUSION

A hybrid protein between K. lactis and A. niger beta-galactosidases was constructed that increases the yield of the protein released to the growth medium. Modifications introduced in the construction, besides to improve secretion, conferred to the protein biochemical characteristics of biotechnological interest.