The Discoidin Domain of Bacillus circulans β-Galactosidase Plays an Essential Role in Repressing Galactooligosaccharide Production

Identification of α-L-fucosidase (ALFuc) of Blastocystis sp. subtypes ST1, ST2 and ST3

Blastocystis sp. is a common intestinal microorganism. The α-L-fucosidase (ALFuc) is an enzyme long associated with the colonization of the gut microbiota. However, this enzyme has not been experimentally identified in Blastocystis cultures. The objective of the present study was to identify ALFuc in supernatants of axenic cultures of Blastocystis subtype (ST)1 ATCC-50177 and ATCC-50610 and to compare predicted ALFuc proteins of alfuc genes in sequenced STs1–3 isolates in human Blastocystis carriers. Excretion/secretion (Es/p) and cell lysate proteins were obtained by processing Blastocystis ATCC cultures and submitting them to SDS–PAGE and immunoblotting. In addition, 18 fecal samples from symptomatic Blastocystis human carriers were analyzed by sequencing of amplification products for subtyping. A complete identification of the alfuc gene and phylogenetic analysis were performed. Immunoblotting showed that the amplified band corresponding to ALFuc (~51 kDa) was recognized only in the ES/p. Furthermore, prediction analysis of ALFuc 3D structures revealed that the domain α-L-fucosidase and the GH29 family's catalytic sites were conserved; interestingly, the galactose-binding domain was recognized only in ST1 and ST2. The phylogenetic inferences of ALFuc showed that STs1–3 were clearly identifiable and grouped into specific clusters. Our results show, for the first time through experimental data that ALFuc is a secretion product of Blastocystis sp., which could have a relevant role during intestinal colonization; however, further studies are required to clarify this condition. Furthermore, the alfuc gene is a promising candidate for a phylogenetic marker, as it shows a conserved classification with the SSU-rDNA gene.

High Galacto-Oligosaccharide Production and a Structural Model for Transgalactosylation of β-Galactosidase II from Bacillus circulans

The transgalactosylase activity of β-galactosidase produces galacto-oligosaccharides (GOSs) with prebiotic effects similar to those of major oligosaccharides in human milk. β-Galactosidases from Bacillus circulans ATCC 31382 are important enzymes in industrial-scale GOS production. Here, we show the high GOS yield of β-galactosidase II from B. circulans (β-Gal-II, Lactazyme-B), compared to other commercial enzymes. We also determine the crystal structure of the five conserved domains of β-Gal-II in an apo-form and complexed with galactose and an acceptor sugar, showing the heterogeneous mode of transgalactosylation by the enzyme. Truncation studies of the five conserved domains reveal that all five domains are essential for enzyme catalysis, while some truncated constructs were still expressed as soluble proteins. Structural comparison of β-Gal-II with other β-galactosidase homologues suggests that the GOS linkage preference of the enzyme might be quite different from other enzymes. The structural information on β-Gal-II might provide molecular insights into the transgalactosylation process of the β-galactosidases in GOS production.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Biochemical Characterization of the Functional Roles of Residues in the Active Site of the β-Galactosidase from Bacillus circulans ATCC 31382

The β-galactosidase enzyme from Bacillus circulans ATCC 31382 BgaD is widely used in the food industry to produce prebiotic galactooligosaccharides (GOS). Recently, the crystal structure of a C-terminally truncated version of the enzyme (BgaD-D) has been elucidated. The roles of active site amino acid residues in β-galactosidase enzyme reaction and product specificity have remained unknown. On the basis of a structural alignment of the β-galactosidase enzymes BgaD-D from B. circulans and BgaA from Streptococcus pneumoniae, and the complex of BgaA with LacNAc, we identified eight active site amino acid residues (Arg185, Asp481, Lys487, Tyr511, Trp570, Trp593, Glu601, and Phe616) in BgaD-D. This study reports an investigation of the functional roles of these residues, using site-directed mutagenesis, and a detailed biochemical characterization and product profile analysis of the mutants obtained. The data show that these residues are involved in binding and positioning of the substrate and thus determine the BgaD-D activity and product linkage specificity. This study provides detailed insights into the structure-function relationships of the B. circulans BgaD-D enzyme, especially regarding GOS product linkage specificity, allowing the rational mutation of β-galactosidase enzymes to produce specific mixtures of GOS structures.

Engineering of the Bacillus circulans β-Galactosidase Product Specificity

Microbial β-galactosidase enzymes are widely used as biocatalysts in industry to produce prebiotic galactooligosaccharides (GOS) from lactose. GOS mixtures are used as beneficial additives in infant formula to mimic the prebiotic effects of human milk oligosaccharides (hMOS). The structural variety in GOS mixtures is significantly lower than in hMOS. Since this structural complexity is considered as the basis for the multiple biological functions of hMOS, it is important to broaden the variety of GOS structures. In this study, residue R484 near +1 subsite of the C-terminally truncated β-galactosidase from Bacillus circulans (BgaD-D) was subjected to site saturation mutagenesis. Especially the R484S and R484H mutant enzymes displayed significantly altered enzyme specificity, leading to a new type of GOS mixture with altered structures and linkage types. The GOS mixtures produced by these mutant enzymes contained 14 structures that were not present in the wild-type enzyme GOS mixture; 10 of these are completely new structures. The GOS produced by these mutant enzymes contained a combination of (β1 → 3) and (β1 → 4) linkages, while the wild-type enzyme has a clear preference toward (β1 → 4) linkages. The yield of the trisaccharide β-d-Galp-(1 → 3)-β-d-Galp-(1 → 4)-d-Glcp produced by mutants R484S and R484H increased 50 times compared to that of the wild-type enzyme. These results indicate that residue R484 is crucial for the linkage specificity of BgaD-D. This is the first study showing that β-galactosidase enzyme engineering results in an altered GOS linkage specificity and product mixture. The more diverse GOS mixtures produced by these engineered enzymes may find industrial applications.

Variations in prebiotic oligosaccharide fermentation by intestinal lactic acid bacteria

Prebiotic oligosaccharides confer health benefits on the host by modulating the gut microbiota. Intestinal lactic acid bacteria (LAB) are potential targets of prebiotics; however, the metabolism of oligosaccharides by LAB has not been fully characterized. Here, we studied the metabolism of eight oligosaccharides by 19 strains of intestinal LAB. Among the eight oligosaccharides used, 1-kestose, lactosucrose and galactooligosaccharides (GOSs) led to the greatest increases in the numbers of the strains tested. However, mono- and disaccharides accounted for more than half of the GOSs used, and several strains only metabolized the mono- and di-saccharides in GOSs. End product profiles indicated that the amounts of lactate produced were generally consistent with the bacterial growth recorded. Oligosaccharide profiling revealed the interesting metabolic manner in Lactobacillus paracasei strains, which metabolized all oligosaccharides, but left sucrose when cultured with fructooligosaccharides. The present study clearly indicated that the prebiotic potential of each oligosaccharide differs.