High yield production of a soluble bifidobacterial β-galactosidase (BbgIV) in E. coli DH5α with improved catalytic efficiency for the synthesis of prebiotic galactooligosaccharides

Potential applications of recombinant bifidobacterial proteins in the food industry, biomedicine, process innovation and glycobiology

Bifidobacterial proteins have been widely studied to elucidate the metabolic mechanisms of diet adaptation and survival of Bifidobacteria, among others. The use of heterologous expression systems to obtain proteins in sufficient quantities to be characterized has been essential in these studies. L. lactis and the same Bifidobacterium as expression systems highlight ways to corroborate some of the functions attributed to these proteins. The most studied proteins are enzymes related to carbohydrate metabolism, particularly glycosidases, due to their potential application in the synthesis of neoglycoconjugates, prebiotic neooligosaccharides, and active metabolites as well as their high specificity and efficiency in processing glycoconjugates. In this review, we classified the recombinant bifidobacterial proteins reported to date whose characterization has demonstrated their usefulness or their ability to produce a product of commercial interest for the food industry, biomedicine, process innovation and glycobiology. Future directions for their study are also discussed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-021-00957-1.

Screening novel β-galactosidases from a sequence-based metagenome and characterization of an alkaline β-galactosidase for the enzymatic synthesis of galactooligosaccharides

βgalactosidases have wide industrial applications in lactose hydrolysis and transglycosylation reactions. Therefore, there is a need to mine novel and high-quality β-galactosidases with good tolerance and novel features from harsh environments and genomic databases. In this study, an Escherichia coli β-galactosidase-deficient host, ΔlacZ(DE3)pRARE, was constructed by the CRISPR-Cas9 system for screening active β-galactosidases. Of thirty selected β-galactosidases, twelve novel enzymes showed β-galactosidase activity, four of which were purified for further study. BGal_375 exhibited maximal activity at pH 8 and 50 °C. The concentrations of two types of galactooligosaccharides, tri- and tetra-saccharides, produced by BGal_375, reached 64.53 g/l and 8.32 g/l, respectively. BGal_375 displayed a K_m value of 1.65 mM and k_cat value of 53 s^-1 for p-nitrophenyl-β-d-galactopyranoside (pNPG). BGal_137, BGal_144-3, and BGal_145-2 showed promising hydrolytic activity for pNPG. BGal_137 is a homodimer while BGal_144-3, BGal_145-2, and BGal_375 were all monomeric. This study provided an efficient solution for the identification of new β-galactosidases from metagenomic data, and an alkaline β-galactosidase efficient for the synthesis of galactooligosaccharides was obtained, which is important for potential industrial applications.

Two β-galactosidases from the human isolate Bifidobacterium breve DSM 20213: molecular cloning and expression, biochemical characterization and synthesis of galacto-oligosaccharides

Two β-galactosidases, β-gal I and β-gal II, from Bifidobacterium breve DSM 20213, which was isolated from the intestine of an infant, were overexpressed in Escherichia coli with co-expression of the chaperones GroEL/GroES, purified to electrophoretic homogeneity and biochemically characterized. Both β-gal I and β-gal II belong to glycoside hydrolase family 2 and are homodimers with native molecular masses of 220 and 211 kDa, respectively. The optimum pH and temperature for hydrolysis of the two substrates o-nitrophenyl-β-D-galactopyranoside (oNPG) and lactose were determined at pH 7.0 and 50°C for β-gal I, and at pH 6.5 and 55°C for β-gal II, respectively. The kcat/Km values for oNPG and lactose hydrolysis are 722 and 7.4 mM-1s-1 for β-gal I, and 543 and 25 mM-1s-1 for β-gal II. Both β-gal I and β-gal II are only moderately inhibited by their reaction products D-galactose and D-glucose. Both enzymes were found to be very well suited for the production of galacto-oligosaccharides with total GOS yields of 33% and 44% of total sugars obtained with β-gal I and β-gal II, respectively. The predominant transgalactosylation products are β-D-Galp-(1→6)-D-Glc (allolactose) and β-D-Galp-(1→3)-D-Lac, accounting together for more than 75% and 65% of the GOS formed by transgalactosylation by β-gal I and β-gal II, respectively, indicating that both enzymes have a propensity to synthesize β-(1→6) and β-(1→3)-linked GOS. The resulting GOS mixtures contained relatively high fractions of allolactose, which results from the fact that glucose is a far better acceptor for galactosyl transfer than galactose and lactose, and intramolecular transgalactosylation contributes significantly to the formation of this disaccharide.