Galacto-oligosaccharide hydrolysis by genetically-engineered alpha-galactosidase-producing Pseudomonas chlororaphis strains

Molecular advances in microbial α-galactosidases: challenges and prospects

α-Galactosidase (α-D-galactosidase galactohydrolase; EC 3.2.1.22), is an industrially important enzyme that hydrolyzes the galactose residues in galactooligosaccharides and polysaccharides. The industrial production of α-galactosidase is currently insufficient owing to the high production cost, low production efficiency and low enzyme activity. Recent years have witnessed an increase in the worldwide research on molecular techniques to improve the production efficiency of microbial α-galactosidases. Cloning and overexpression of the gene sequences coding for α-galactosidases can not only increase the enzyme yield but can confer industrially beneficial characteristics to the enzyme protein. This review focuses on the molecular advances in the overexpression of α-galactosidases in bacterial and yeast/fungal expression systems. Recombinant α-galactosidases have improved biochemical and hydrolytic properties compared to their native counterparts. Metabolic engineering of microorganisms to produce high yields of α-galactosidase can also assist in the production of value-added products. Developing new variants of α-galactosidases through directed evolution can yield enzymes with increased catalytic activity and altered regioselectivity. The bottlenecks in the recombinant production of α-galactosidases are also discussed. The knowledge about the hurdles in the overexpression of recombinant proteins illuminates the emerging possibilities of developing a successful microbial cell factory and widens the opportunities for the production of industrially beneficial α-galactosidases.

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.