Human milk oligosaccharides (HMOs) constitute a unique family of bioactive lactose-based molecules present in human breast milk. HMOs are of major importance for infant health and development but also virtually absent from bovine milk used for infant formula. Among the HMOs, the fucosylated species are the most abundant. Transfucosylation catalysed by retaining α-l-fucosidases is a new route for manufacturing biomimetic HMOs. Seven α-l-fucosidases from glycosyl hydrolase family 29 were expressed, characterized in terms of substrate specificity and thermal stability, and shown to be able to catalyse transfucosylation. The α-l-1,3/4-fucosidase CpAfc2 from Clostridium perfringens efficiently catalysed the formation of the more complex human milk oligosaccharide structure lacto-N-fucopentaose II (LNFP II) using 3-fucosyllactose as fucosyl donor and lacto-N-tetraose as acceptor with a 39% yield. α-l-Fucosidases FgFCO1 from Fusarium graminearum and Mfuc5 from a soil metagenome were able to catalyse transfucosylation of lactose using citrus xyloglucan as fucosyl donor. FgFCO1 catalysed formation of 2'-fucosyllactose, whereas Mfuc5 catalysis mainly produced an unidentified, non-HMO fucosyllactose, reaching molar yields based on the donor substrate of 14% and 18%, respectively.

BackgroundCarbohydrate-active enzymes are found in all organisms and participate in key biological processes. These enzymes are classified in 274 families in the CAZy database but the sequence diversity within each family makes it a major task to identify new family members and to provide basis for prediction of enzyme function. A fast and reliable method for de novo annotation of genes encoding carbohydrate-active enzymes is to identify conserved peptides in the curated enzyme families followed by matching of the conserved peptides to the sequence of interest as demonstrated for the glycosyl hydrolase and the lytic polysaccharide monooxygenase families. This approach not only assigns the enzymes to families but also provides functional prediction of the enzymes with high accuracy.ResultsWe identified conserved peptides for all enzyme families in the CAZy database with Peptide Pattern Recognition. The conserved peptides were matched to protein sequence for de novo annotation and functional prediction of carbohydrate-active enzymes with the Hotpep method. Annotation of protein sequences from 12 bacterial and 16 fungal genomes to families with Hotpep had an accuracy of 0.84 (measured as F1-score) compared to semiautomatic annotation by the CAZy database whereas the dbCAN HMM-based method had an accuracy of 0.77 with optimized parameters. Furthermore, Hotpep provided a functional prediction with 86% accuracy for the annotated genes. Hotpep is available as a stand-alone application for MS Windows.ConclusionsHotpep is a state-of-the-art method for automatic annotation and functional prediction of carbohydrate-active enzymes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-017-1625-9) contains supplementary material, which is available to authorized users.

This paper describes the discovery of novel α-L-fucosidases and evaluation of their potential to catalyse the transglycosylation reaction leading to production of fucosylated human milk oligosaccharides. Seven novel α-L-fucosidase-encoding genes were identified by functional screening of a soil-derived metagenome library and expressed in E. coli as recombinant 6xHis-tagged proteins. All seven fucosidases belong to glycosyl hydrolase family 29 (GH 29). Six of the seven α-L-fucosidases were substrate-inhibited, moderately thermostable and most hydrolytically active in the pH range 6–7, when tested with para-nitrophenyl-α-L-fucopyranoside (pNP-Fuc) as the substrate. In contrast, one fucosidase (Mfuc6) exhibited a high pH optimum and an unusual sigmoidal kinetics towards pNP-Fuc substrate. When tested for trans-fucosylation activity using pNP-Fuc as donor, most of the enzymes were able to transfer fucose to pNP-Fuc (self-condensation) or to lactose. With the α-L-fucosidase from Thermotoga maritima and the metagenome-derived Mfuc5, different fucosyllactose variants including the principal fucosylated HMO 2’-fucosyllactose were synthesised in yields of up to ~6.4%. Mfuc5 was able to release fucose from xyloglucan and could also use it as a fucosyl-donor for synthesis of fucosyllactose. This is the first study describing the use of glycosyl hydrolases for the synthesis of genuine fucosylated human milk oligosaccharides.

The ability to modulate gene expression is an important genetic tool in systems biology and biotechnology. Here, we demonstrate that a previously published easy and fast PCR-based method for modulating gene expression in lactic acid bacteria is also applicable to Corynebacterium glutamicum. We constructed constitutive promoter libraries based on various combinations of a previously reported C. glutamicum -10 consensus sequence (gngnTA(c/t)aaTgg) and the Escherichia coli -35 consensus, either with or without an AT-rich region upstream. A promoter library based on consensus sequences frequently found in low-GC Gram-positive microorganisms was also included. The strongest promoters were found in the library with a -35 region and a C. glutamicum -10 consensus, and this library also represents the largest activity span. Using the alternative -10 consensus TATAAT, which can be found in many other prokaryotes, resulted in a weaker but still useful promoter library. The upstream AT-rich region did not appear to affect promoter strength in C. glutamicum. In addition to the constitutive promoters, a synthetic inducible promoter library, based on the E. coli lac-promoter, was constructed by randomizing the 17-bp spacer between -35 and -10 consensus sequences and the sequences surrounding these. The inducible promoter library was shown to result in β-galactosidase activities ranging from 284 to 1,665 Miller units when induced by IPTG, and the induction fold ranged from 7-59. We find that the synthetic promoter library (SPL) technology is convenient for modulating gene expression in C. glutamicum and should have many future applications, within basic research as well as for optimizing industrial production organisms.

This paper describes the discovery and characterization of two novel β-N-acetylhexosaminidases HEX1 and HEX2, capable of catalyzing the synthesis of human milk oligosaccharides (HMO) backbone structures with fair yields using chitin oligomers as β-N-acetylglucosamine (GlcNAc) donor. The enzyme-encoding genes were identified by functional screening of a soil-derived metagenomic library. The β-N-acetylhexosaminidases were expressed in Escherichia coli with an N-terminal His6-tag and were purified by nickel affinity chromatography. The sequence similarities of the enzymes with their respective closest homologues are 59 % for HEX1 and 51 % for HEX2 on the protein level. Both β-N-acetylhexosaminidases are classified into glycosyl hydrolase family 20 (GH 20) are able to hydrolyze para-nitrophenyl-β-N-acetylglucosamine (pNP-GlcNAc) as well as para-nitrophenyl-β-N-acetylgalactosamine (pNP-GalNAc) and exhibit pH optima of 8 and 6 for HEX1 and HEX2, respectively. The enzymes are able to hydrolyze N-acetylchitooligosaccharides with a degree of polymerization of two, three, and four. The major findings were, that HEX1 and HEX2 catalyze trans-glycosylation reactions with lactose as acceptor, giving rise to the human milk oligosaccharide precursor lacto-N-triose II (LNT2) with yields of 2 and 8 % based on the donor substrate. In total, trans-glycosylation reactions were tested with the disaccharide acceptors β-lactose, sucrose, and maltose, as well as with the monosaccharides galactose and glucose resulting in the successful attachment of GlcNAc to the acceptor in all cases.