A Review on the Various Sources of β-Galactosidase and Its Lactose Hydrolysis Property

Efficient Mutagenesis Strategy Based on Nonpolar Amino Acids Scanning for the Improvement of Transglycosylation Ability of β-Galactosidases

A commercial β-galactosidase from Aspergillus oryzae was genetically modified through semirational design to enhance its transglycosylation ability for galactooligosaccharides (GOSs) production. By disrupting hydrogen bonds, altering the hydrophobicity and enlarging the catalytic pocket, 12 single-point mutants and a combinatorial mutant (M3) with enhanced transgalactosylation abilities were obtained. Mutant M3 was successfully expressed in Aspergillus niger, and a β-galactosidase production of 228.2 U/mL was achieved. M3 efficiently catalyzed the synthesis of GOSs, with a high yield of 62.3% (w/w), which was comparable to that of the highest value for GOS production (63.3%, w/w) ever reported. Structural analysis revealed that weak enzyme-galactose interaction and high hydrophobicity of the catalytic pocket may contribute to the enhancement of transgalactosylation ability of AoBgal35A. Thus, a mutagenesis strategy named nonpolar amino acids scanning was constructed on the basis of adjusting enzyme-galactose interaction as well as the hydrophobicity of the catalytic pocket. To validate the strategy, 3 β-galactosidases were further modified and the GOS yields of 2 were improved by 30-40%. This study may provide an excellent catalyst for commercial GOS production as well as a rapid strategy for the modification of β-galactosidases.

Two novel β-galactosidases from Aeromonas caviae with potential industrial applications in milk and catalytic mechanism analysis using molecular docking

Lactose intolerance has been a significant global health concern, as it is caused by the absence of lactase, leading to the inability of the human body to absorb lactose. This study investigated two genes encoding maltose O-acetyltransferase with β-galactosidase activity from Aeromonas caviae to evaluate their potential application value for lactose degradation in bovine and human milk. The two novel β-galactosidases (AcGal25: 22.0 kDa and AcGal31: 21.3 kDa) were heterologously expressed and biochemically characterized. The optimal pH of both enzymes was 8.0, and the optimal temperature of AcGal25 and AcGal31 were 45 and 42 °C, respectively. Fe2+ and Mn2+ significantly promoted the activity of both enzymes. The two enzymes kept over 75 % activity after incubation for 30 days at 45 °C. HPLC results showed that lactose in bovine milk was completely hydrolyzed by AcGal31 when reacted for 6 h, and about 5 % lactose in human milk was left. The docking results showed that AcGal31 has a more vital lactose-binding ability than AcGal25. LYS129 and ARG165 are highly likely catalytic sites of AcGal31. AcGal31 demonstrated excellent commercial value in making lactose-free milk.

Computational pipeline for sustainable enzyme discovery through (re)use of metagenomic data

Enzymes derived from extremophilic organisms, also known as extremozymes, offer sustainable and efficient solutions for industrial applications. Valued for their resilience and low environmental impact, extremozymes have found use as catalysts in various processes, ranging from dairy production to pharmaceutical manufacturing. However, discovery of novel extremozymes is often hindered by challenges such as culturing difficulties, underrepresentation of extreme environments in reference databases, and limitations of traditional sequence-based screening methods. In this work, we present a computational pipeline designed to discover novel enzymes from metagenomic data derived from extreme environments. This pipeline represents a versatile and sustainable approach that promotes reuse and recycling of existing datasets and minimises the need for additional environmental sampling. In its core, the algorithm integrates both traditional bioinformatic techniques and recent advances in structural prediction, enabling rapid and accurate identification of enzymes. However, due to its design, the algorithm relies heavily on existing databases, which can limit its effectiveness in situations where reference data is scarce or when encountering novel protein families. As a proof-of-concept, we applied the pipeline to metagenomic data from deep-sea hydrothermal vents, with a focus on β-galactosidases. The pipeline identified 11 potential candidate proteins, out of which 10 showed in vitro activity. One of the selected enzymes, βGal_UW07, showed strong potential for industrial applications. The enzyme exhibited optimal activity at 70 °C and was exceptionally resistant to high pH and the presence of metal ions and reducing agents. Overall, our results indicate that the pipeline is highly accurate and can play a key role in sustainable bioprospecting, leveraging existing metagenomic datasets and minimising in situ interventions in pristine regions.

C-terminal domains of β-galactosidase from Paenibacillus macquariensis modulate product distribution by altering substrate binding conformation

GH2 β-galactosidases synthesize galacto-oligosaccharides (GOS) with various degrees of polymerization and linkage types. For some GH2 multidomain β-galactosidases, catalytic efficiency and size of product oligosaccharides can be modified by truncating the C-terminal domains. Yet, the impact of C-terminal truncation on product linkage distribution remains unexplored, and the mechanisms behind this strategy are not entirely understood. Investigating how C-terminal truncation affects GOS synthesis is important for producing desired product structures. Herein, we expressed the GH2 β-galactosidase PmGal and analyzed the product distribution of both the wild-type enzyme and its C-terminally truncated forms. One of these variants showed enhanced specific activity and increased allolactose productivity. Through molecular dynamics analysis, we examined the functional roles of the C-terminal domains. Our findings reveal that truncation increases the flexibility of both the active-site loops in the catalytic domain and the surface loop in the C-terminal domain via dynamic allostery. The enhanced flexibility alters the relative positioning of the C-terminus and catalytic domain, and influences substrate binding conformation, resulting in a shift in product distribution. Overall, our study provides valuable insights into truncation strategies for controlling transgalactosylation efficiency and product distribution. It also enhances our understanding of the structural factors influencing β-galactosidase catalysis.

A near-infrared fluorescent probe toward β-Gal with dual-targeting potential of hepatocytes and lysosomes: Design, synthesis, and evaluation

In this work, a novel near-infrared fluorescent probe of benzopyranonitrile toward β-Gal was developed with high selectivity and low detection limits. DCM-Mor-Gal could effectively distinguish hepatocellular cells (HepG2) from SGC7901, HeLa, A549, and human normal liver cells (HL-7702) under the mediation of the galactose group, and effectively aggregate in the lysosomes under the acidity-alkalinity attraction, showing a notable dual-targeting potential of hepatocytes and lysosomes. The zebrafish experiments confirmed the utility of DCM-Mor-Gal in detecting β-Gal in vivo, which is expected to be an effective tool for the clinical detection of related diseases.

Metabolic profiling reveals distinctive ripening dynamics in ethylene-treated Musa balbisiana cv. 'Pisang Klutuk Wulung' compared to commercial Cavendish banana

As an important crop, bananas still encounter fruit quality and shelf-life problems that are affected by the ripening process. Improving postharvest technologies may effectively address these challenges, such as by studying the ripening mechanism of banana cultivars with a slow ripening process. A banana cultivar that exhibits this characteristic is Musa balbisiana cv. 'Pisang Klutuk Wulung' (BB Group) or Pisang Klutuk Wulung (PKW), which has a ripening duration of 14-28 days. However, the metabolomics study on the ripening mechanism of this banana is still limited. This study aimed to analyze metabolite changes in ethylene-treated Pisang Klutuk Wulung during ripening in comparison to commercial bananas (Cavendish). Both bananas were subjected to exogenous ethylene treatment and analyzed using gas chromatography-mass spectrometry to perform metabolite profiling throughout the ripening process. The principal component analysis showed sample separation based on the ripening stages and banana species in pulp and peel. Orthogonal projection to latent structure analysis suggested that metabolite changes accompanied the ripening stages. Potential metabolite markers that distinguished the ripening of PKW and Cavendish were found, such as quinic acid, inositol, and 2-aminoethanol. This study shows differences in metabolite profiles between these bananas, especially the metabolites involved in sugar metabolism, cell wall metabolism, stress response, and biosynthesis of aromatic compounds. This study provides novel insights into the metabolic changes occurring during PKW ripening, contributing to the improvement of banana postharvest strategies.

In-Gel Activity Assay for Glycosidases

Fluorogenic sugar derivatives are useful substrates for the detection of glycosidase activity within a native polyacrylamide gel. When an enzyme cleaves the glycosidic bond, a fluorescent compound is released at the protein's location, forming a band visible under UV light. This method can be used to identify proteins with glycosidase activity within a mixture, evaluate the effect of mutations on enzyme activity, and even provide information about the quaternary structure of a glycosidase. Here, we present a protocol for glycosidase zymography and demonstrate its utility as a tool to probe the active oligomeric form of a novel bacterial β-galactosidase.

Modular and Fast Assembly of Self-Immobilizing Fluorogenic Probes for β-Galactosidase Detection

β-Galactosidase (β-gal) has emerged as a pivotal biomarker in primary ovarian cancer. Despite the existence of numerous fluorescent probes for β-gal activity detection, quinone methide-based immobilizing probes were shown to avoid rapid diffusion of the activated fluorophore and improve the resolution. However, the synthesis of these fluorophores, particularly near-infrared fluorophores, still exhibits lower efficiency. In this study, we introduce modular and rapidly assembled self-immobilizing fluorogenic probes, capitalizing on the proximity labeling properties of quinone methide (QM). Compared to conventional fluorescent probes, these new probes not only exhibit a fluorogenic response but also achieve permanent retention, demonstrating improved detection sensitivity, particularly after cell fixation and in vivo animal model studies. This straightforward synthesis approach holds promise for broader applications in detecting other analytes.

Inhibitory Effects on RNA Binding and RNase H Induction Activity of Prodrug-Type Oligodeoxynucleotides Modified with a Galactosylated Self-Immolative Linker Cleavable by β-Galactosidase

Prodrug-type oligonucleotides (prodrug-ONs) are a class of oligonucleotide designed for activation under specific intracellular conditions or external stimuli. Prodrug-ONs can be activated in the target tissues or cells, thereby reducing the risk of adverse effects. In this study, we synthesized prodrug-type oligodeoxynucleotides activated by β-galactosidase, an enzyme that is overexpressed in cancer and senescent cells. These oligodeoxynucleotides (ODNs) contain a modified thymidine conjugated with galactose via a self-immolative linker at the O4-position. UV-melting analysis revealed that the modifications decreased the melting temperature (Tm) compared with that of the unmodified ODN when hybridized with complementary RNA. Furthermore, cleavage of the glycosidic bond by β-galactosidase resulted in the spontaneous removal of the linker from the nucleobase moiety, generating unmodified ODNs. Additionally, the introduction of multiple modified thymidines into ODNs completely inhibited the RNase H-mediated cleavage of complementary RNA. These findings suggest the possibility of developing prodrug-ONs, which are specifically activated in cancer cells or senescent cells with high β-galactosidase expression.

An activatable fluorescence probe for rapid detection and in situ imaging of β-galactosidase activity in cabbage roots under heavy metal stress

β-Galactosidase (β-gal), an enzyme related to cell wall degradation, plays an important role in regulating cell wall metabolism and reconstruction. However, activatable fluorescence probes for the detection and imaging of β-gal fluctuations in plants have been less exploited. Herein, we report an activatable fluorescent probe based on intramolecular charge transfer (ICT), benzothiazole coumarin-bearing β-galactoside (BC-βgal), to achieve distinct in situ imaging of β-gal in plant cells. It exhibits high sensitivity and selectivity to β-gal with a fast response (8 min). BC-βgal can be used to efficiently detect the alternations of intracellular β-gal levels in cabbage root cells with considerable imaging integrity and imaging contrast. Significantly, BC-βgal can assess β-gal activity in cabbage roots under heavy metal stress (Cd2+, Cu2+, and Pb2+), revealing that β-gal activity is negatively correlated with the severity of heavy metal stress. Our work thus facilitates the study of β-gal biological mechanisms.

A novel NIR fluorescent probe for enhanced β-galactosidase detection and tumor imaging in ovarian cancer models

The advancement of biological imaging techniques critically depends on the development of novel near-infrared (NIR) fluorescent probes. In this study, we introduce a designed NIR fluorescent probe, NRO-βgal, which exhibits a unique off-on response mechanism to β-galactosidase (β-gal). Emitting a fluorescence peak at a wavelength of 670 nm, NRO-βgal showcases a significant Stokes shift of 85 nm, which is indicative of its efficient energy transfer and minimized background interference. The probe achieves a remarkably low in vitro detection limit of 0.2 U/L and demonstrates a rapid response within 10 min, thereby underscoring its exceptional sensitivity, selectivity, and operational swiftness. Such superior analytical performance broadens the horizon for its application in intricate biological imaging studies. To validate the practical utility of NRO-βgal in bio-imaging, we employed ovarian cancer cell and mouse models, where the probe's efficacy in accurately delineating tumor cells was examined. The results affirm NRO-βgal's capability to provide sharp, high-contrast images of tumor regions, thereby significantly enhancing the precision of surgical tumor resection. Furthermore, the probe's potential for real-time monitoring of enzymatic activity in living tissues underscores its utility as a powerful tool for diagnostics in oncology and beyond.

Environmentally responsive changes in mucus indicators and microbiota of Chinese sturgeon Acipensersinensis

The impact of environmental factors on the health of the endangered Chinese sturgeon (Acipenser sinensis) and the potential hazards associated with sample collection for health monitoring pose urgent need to its conservation. In this study, Chinese sturgeons were selected from indoor and outdoor environments to evaluate metabolic and tissue damage indicators, along with a non-specific immune enzyme in fish mucus. Additionally, the microbiota of both water bodies and fish mucus were determined using 16S rRNA high-throughput sequencing. The correlation between the indicators and the microbiota was investigated, along with the measurement of multiple environmental factors. The results revealed significantly higher levels of two metabolic indicators, total protein (TP) and cortisol (COR) in indoor fish mucus compared to outdoor fish mucus (p < 0.05). The activities of acid phosphatase (ACP), alkaline phosphatase (ALP), creatine kinase (CK), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) were significantly higher in indoor fish, serving as indicators of tissue damage (p < 0.05). The activity of lysozyme (LZM) was significantly lower in indoor fish (p < 0.01). Biomarker analysis at the phylum and genus levels in outdoor samples revealed that microorganisms were primarily related to the catabolism of organic nutrients. In indoor environments, microorganisms displayed a broader spectrum of functions, including ecological niche establishment, host colonization, potential pathogenicity, and antagonism of pathogens. KEGG functional enrichment corroborated these findings. Dissolved oxygen (DO), electrical conductivity (EC), ammonia nitrogen (NH3-N), turbidity (TU), and chemical oxygen demand (COD) exerted effects on outdoor microbiota. Temperature (TEMP), nitrate (NO3-), total phosphorus (TP), and total nitrogen (TN) influenced indoor microbiota. Changes in mucus indicators, microbial structure, and function in both environments were highly correlated with these factors. Our study provides novel insights into the health impacts of different environments on Chinese sturgeon using a non-invasive method.

The covalent immobilization of β-galactosidase from Aspergillus oryzae and alkaline protease from Bacillus licheniformis on amino-functionalized multi-walled carbon nanotubes in milk

This study aimed was to covalently immobilize β-galactosidase from Aspergillus oryzae and protease from Bacillus licheniformis on amino-functionalized multi-walled carbon nanotubes. In this study, a two-level factorial design was employed to investigate the impact of seven continuous variables (activation pH, glutaraldehyde molarity, activation time (0-8 h), buffer solution pH (8-0), buffer solution molarity, MWCNT-NH 2 -glutaraldehyde quantity, and stabilization time (0-180 h)) on the immobilization efficiency and enzymatic activity of protease and β-galactosidase. Furthermore, the effect of time on the percentage of enzymatic activity was examined during specific intervals (24, 48, 72, 96, and 120 h) of the immobilization process. The analysis of variance results for protease enzymatic activity revealed a notable influence of the seven variables on immobilization efficiency and enzymatic activity. Additionally, the findings indicate that activation time, buffer pH, MWCNT-NH 2 -glutaraldehyde quantity, and stabilization time significantly affect the activity of the protease enzyme. The interplay between buffer pH and stabilization time is also significant. Indeed, both activation time and the quantity of MWCNT-NH 2 -glutaraldehyde exert a reducing effect on enzyme activity. Notably, the influence of MWCNT-NH 2 -glutaraldehyde quantity is more significant (p < 0.05). In terms of beta-galactosidase enzymatic activity, the study results highlight that among the seven variables considered, only the glutaraldehyde molarity, activation time, and the interplay of activation time and the quantity of MWCNT-NH 2 -glutaraldehyde can exert a statistically significant positive impact on the enzyme's activity (p < 0.05). The combination of activation time and buffer solution molarity, as well as the interactive effect of buffer pH and MWCNT-NH2-glutaraldehyde, can lead to a significant improvement in the stabilization efficiency of the protease of carbon nanotubes. The analysis of variance results demonstrated that the efficiency of covalently immobilizing β-galactosidase from Aspergillus oryzae on amino-functionalized multi-walled carbon nanotubes is influenced by the molarity of glutaraldehyde, buffer pH, stabilization time, and the interplay of activation time + buffer pH, buffer pH + activation time, activation time + buffer molarity, and glutaraldehyde molarity + MWCNT-NH 2 -glutaraldehyde (p < 0.05). Through the optimization and selection of optimal formulations, the obtained results indicate enzyme activities and stabilization efficiencies of 64.09 % ± 72.63 % and 65.96 % ± 71.77 % for protease and beta-galactosidase, respectively. Moreover, increasing the enzyme stabilization time resulted in a reduction of enzyme activity. Furthermore, an increase in pH, temperature, and the duration of milk storage passing through the enzyme-immobilized carbon nanotubes led to a decrease in enzyme stabilization efficiency, and lactose hydrolysis declined progressively over 8-h. Hence, the covalent immobilization of β-galactosidase from Aspergillus oryzae and protease from Bacillus licheniformis onto amino-functionalized multi-walled carbon nanotubes is anticipated to be achievable for milk applications.

Enzyme stability in polymer hydrogel-enzyme hybrid nanocarrier containing phosphorylcholine group

Enzymes are biological catalysts with good biocompatibility and high efficiency and have been widely used in many fields, such as wastewater treatment, biosensors, and the medical industry. However, their inherently low stability under conditions of practical use limits further applications. Zwitterionic polymers possessing a pair of oppositely charged groups in their repeating units can increase protein stability because of their good biocompatibility and high water content. In this study, zwitterionic copolymer nanogels comprising poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-methacrylic acid-N-hydroxy succinimide ester (MNHS)) (PMS) were synthesized via reversible addition-fragmentation chain-transfer polymerization (RAFT). β-Galactosidase (β-gal) was post-modified within zwitterionic polymer nanogels with a covalently-bound spacer and the activity was compared with that of directly immobilized β-gal and free β-gal. Compared with direct immobilization, covalent immobilization with a spacer could reduce the structural change of β-gal, as confirmed by the circular dichroism spectra. Although the activity of β-gal decreased after immobilization, the hybrids of the β-gal immobilized nanogels, termed hybrid nanogel-enzymes, demonstrated superior stability compared to the free enzymes. The hybrid nanogel-enzymes maintained their function against inactivation by organic solvents and proteinases owing to their high water content, anti-biofouling properties, and limited mass transfer. They can also withstand protein aggregation at high temperatures and maintain their activity. Compared to direct immobilization, immobilization with a spacer resulted in a dramatic increase in the enzyme activity and a slight decrease in the stability. These results indicate that polymer nanogels containing phosphorylcholine units are promising materials for enzyme immobilization, expanding the scope of enzyme applications.

Identification and characterization of emGalaseE, a β-1,4 galactosidase from Elizabethkingia meningoseptica, and its application on living cell surface

The biological function of terminal galactose on glycoprotein is an open field of research. Although progress had being made on enzymes that can remove the terminal galactose on glycoproteins, there is a lack of report on galactosidases that can work directly on living cells. In this study, a unique beta 1,4 galactosidase was isolated from Elizabethkingia meningoseptica (Em). It exhibited favorable stability at various temperatures (4-37 °C) and pH (5-8) levels and can remove β-1, 4 linked galactoses directly from glycoproteins. Using Alanine scanning, we found that two acidic residues (Glu-468, and Glu-531) in the predicted active pocket are critical for galactosidase activity. In addition, we also demonstrated that it could cleave galactose residues present on living cell surface. As this enzyme has a potential application for living cell glycan editing, we named it emGalaseE or glycan-editing galactosidase I (csgeGalaseI). In summary, our findings lay the groundwork for further investigation by presenting a simple and effective approach for the removal of galactose moieties from cell surface.