Crystal Structure of α-Galactosidase from Thermus thermophilus: Insight into Hexamer Assembly and Substrate Specificity

Production, purification, characterization, and applications of -galactosidase from Bacillus flexus JS27 isolated from Manikaran hot springs

α-Galactosidase hydrolyzes the α-1,6-linkage present at the non-reducing end of the sugars and results in the release of galactosyl residue from oligosaccharides like melibiose, raffinose, stachyose, etc. In the present study we report, α-galactosidase from Bacillus flexus isolated from Manikaran hot springs (India). Maximum enzyme production was obtained in guar gum and soybean meal after 72 h at 150 rpm. While, the temperature/pH of production was optimized at 50 °C and 7.0, respectively. Isoenzymes (α-gal I and II) were obtained and characterized based on temperature/pH optima along with their stability profile. JS27 α-Gal II was purified with a final purification fold of 11.54. Native and SDS-PAGE were used to determine the molecular weight of the enzyme as 86 and 41 kDa, respectively, indicating its homodimeric form. JS27 α-Gal II showed optimum enzyme activity at 55 °C and pH 7 (10 min). The enzyme displayed K_m value of 2.3809 mM and V_max of 2.0 × 10⁴ µmol/min/ml with pNPG as substrate. JS27 α-Gal II demonstrated substrate hydrolysis and simultaneous formation of transgalactosylation products (α-GOS) with numerous substrates (sugar/sugar alcohols, oligosaccharides, and complex carbohydrates) which were verified by TLC and HPLC analysis. α-GOS are significant functional food ingredients and can be explored as prebiotics.

Microbial α-galactosidases: Efficient biocatalysts for bioprocess technology

Galactomannans, abundantly present in plant biomass, can be used as renewable fermentation feedstock for biorefineries working for the production of bioethanol and other value-added products. The complete and efficient bioconversion of biomass to fermentable sugars for the generation of biofuels and other value-added products require the concerted action of accessory enzymes like α-galactosidases, which can work in cohesion with other carbohydrases in an enzyme cocktail. In the paper industry, α-galactosidases enhance the bleaching effect of endo-β-1,4-mannanases on softwood kraft pulp. Microbial α-galactosidases also find applications in the treatment of legume foods, recovery of sucrose from sugar beet syrup, improving the rheological properties of galactomannans, and synthesis of α-galactooligosaccharides to be used as functional food ingredients. Owing to their industrial applications, there is a surge in the research focused on α-galactosidases. The current review illustrates the diverse industrial applications of microbial α-galactosidases and their challenges and prospects.

Directed evolution of feruloyl esterase from Lactobacillus acidophilus and its application for ferulic acid production

Producing ferulic acid (FA) from the natural substrate with feruloyl esterase is promising in industries, screening and engineering new enzymes with high efficiency to increase the FA yield is of great concern. Here, the feruloyl esterase of Lactobacillus acidophilus (FAELac) was heterologous expressed and the FAELac with different oligomerization states was separated. Interestingly, the activity of dimer was 37-fold higher than high-polymer. To further enhance the efficiency of FAELac, eight mutants were generated based on the simulated structure, of which Q198A, Q134T enhanced the catalytic efficiency by 5.4- and 4.3-fold in comparison with the wild type. Moreover, higher yields of FA (2.21, 6.60, and 1.67 mg/g substrate, respectively) were released by the mutants from de-starched wheat bran, insoluble wheat arabinoxylan, and steam-exploded corn stover. These results indicated that improving the purification process, engineering new FAELac and substrates bias studies hold great potential for increasing FA production yield.

Engineering a Trypsin-Resistant Thermophilic α-Galactosidase to Enhance Pepsin Resistance, Acidic Tolerance, Catalytic Performance, and Potential in the Food and Feed Industry

α-Galactosidase has potential applications, and attempts to improve proteolytic resistance of enzymes have important values. We use a novel strategy for genetic manipulation of a pepsin-sensitive region specific for a pepsin-sensitive but trypsin-resistant high-temperature-active Gal27B from Neosartorya fischeri to screen mutants with enhanced pepsin resistance. All enzymes were produced in Pichia pastoris to identify the roles of loop 4 (Gal27B-A23) and its key residue at position 156 (Gly156Arg/Pro/His) in pepsin resistance. Gal27B-A23 and Gly156Arg/Pro/His elevated pepsin resistance, thermostability, stability at low pH, activity toward raffinose (5.3-6.9-fold) and stachyose (about 1.3-fold), and catalytic efficiencies (up to 4.9-fold). Replacing the pepsin cleavage site Glu155 with Gly improved pepsin resistance but had no effect on pepsin resistance when Arg/Pro/His was at position 156. Thus, pepsin resistance could appear to occur through steric hindrance between the residue at the altered site and neighboring pepsin active site. In the presence of pepsin or trypsin, all mutations increased the ability of Gal27B to hydrolyze galactosaccharides in soybean flour (up to 9.6- and 4.3-fold, respectively) and promoted apparent metabolizable energy and nutrient digestibility in soybean meal for broilers (1.3-1.8-fold). The high activity and tolerance to heat, low pH, and protease benefit food and feed industry in a cost-effective way.