Microbial Synthesis of Lacto-N-fucopentaose I with High Titer and Purity by Screening of Specific Glycosyltransferase and Elimination of Residual Lacto-N-triose II and Lacto-N-tetraose

Glycosyltransferases in human milk oligosaccharide synthesis: structural mechanisms and rational design

Human milk oligosaccharides (HMOs) play a pivotal role in infant health through their multifunctional bioactive properties. Recent advances in synthetic biology have revolutionized microbial platforms for HMO biosynthesis, with glycosyltransferases (GTs) emerging as indispensable biocatalytic tools that drive enzymatic lactose glycosylation to generate diversified oligosaccharides. This review systematically analyzes GT structural biology, elucidating conserved domains and catalytic mechanisms through crystallographic studies. We summarize contemporary optimization strategies for enhancing GT functionality, including solubility enhancement, catalytic efficiency improvement, and substrate specificity engineering via structure-guided rational design. Emerging deep learning algorithms demonstrate transformative potential in GT modifications and de novo design, providing innovative solutions to overcome bottlenecks in industrial-scale HMO synthesis. These approaches establish a framework for the precision engineering of carbohydrate-active enzymes.

Comprehensive review on human Milk oligosaccharides: Biosynthesis, structure, intestinal health benefits, immune regulation, neuromodulation mechanisms, and applications

This review provides a comprehensive analysis of the biosynthetic pathways of various oligosaccharides in Escherichia coli, structural characteristics, and bioactive mechanisms of human milk oligosaccharides (HMOs), with a particular emphasis on their roles in gut health, immune modulation, and neurodevelopment. HMOs primarily function as prebiotics, facilitating the growth of beneficial bacteria such as Bifidobacterium to maintain microbial homeostasis, with a discussion on the synergistic role of carbohydrate-binding modules (CBMs). In immune modulation, HMOs interact with lectins on immune and epithelial cells, influencing immune responses via pathways such as Toll-like receptors (TLRs). Additionally, HMOs have been linked to enhanced cognitive, motor, and language development in infants, influencing genes such as GABRB2, SLC1A7, GLRA4, and CHRM3. The review also examines commercially available HMO-containing products and highlights future research directions and potential applications in nutrition and healthcare.

Efficient Biosynthesis of Sialyllacto-N-tetraose a by a Metabolically Engineered Escherichia coli BL21(DE3) Strain

Recently, the construction of metabolically engineered strains for the microbial synthesis of human milk oligosaccharides (HMOs) has attracted increasing attention. However, fewer efforts were made in the in vivo biosynthesis of complex HMOs, especially sialylated complex HMOs. In this study, we engineered Escherichia coli BL21(DE3) to efficiently produce sialyllacto-N-tetraose a (LST-a) efficiently. Three sequential glycosylation steps were introduced to construct the LST-a pathway, catalyzed by β1,3-N-acetylglucosaminylation, β1,3-galactosylation, and α2,3-sialylation. Pathway genes for cytidine 5'-monophospho (CMP)-N-acetylneuraminic acid (Neu5Ac) were introduced to support the sialylation donor supply. Production of LST-a was improved by deleting competitive genes of CMP-Neu5Ac synthesis, screening a more efficient α2,3-sialyltransferase, and combinatorial optimization of pathway gene expression. LST-a was finally produced with the titer of 1.235 and 4.85 g/L by shake-flask and fed-batch cultivation, respectively, demonstrating the feasibility of efficient microbial production of complex sialylated HMOs.

Highly Efficient In Vivo Production of Sialyllacto-N-tetraose C via Screening of Beneficial β1,4-galactosyltransferase and α2,6-sialyltransferase

Biological production of human milk oligosaccharides (HMOs) using metabolically engineered strains is a research hotspot in food biotechnology, but less effort has been made on the biological production of sialylated complex HMOs. Sialyllacto-N-tetraose c is the only monosialylated complex HMO in the top 15 HMOs. In this study, the metabolic pathway of LST c was constructed in Escherichia coli BL21(DE3) by introducing three sequential glycosyltransferases: β1,3-N-acetylglucosaminyltransferase, β1,4-galactosyltransferase, and α2,6-sialyltransferase. The cytidine 5'-monophospho (CMP)-N-acetylneuraminic acid (Neu5Ac) pathway was enhanced to improve LST c production. The β1,4-galactosyltransferase from Helicobacter pylori J99 (HpGalT) and α2,6-sialyltransferase from Vespertiliibacter pulmonis (ED6ST) were screened as a pair of key glycosyltransferases for enhancing LST c production. The final engineered strain could produce 1.718 and 9.745 g/L LST c by shake-flask and fed-batch cultivation, respectively, indicating the feasibility of efficient biosynthesis of complex sialylated HMOs.

Engineering Escherichia coli for Highly Efficient Biosynthesis of Lacto-N-difucohexaose II through De Novo GDP-l-fucose Pathway

Lacto-N-difucohexaose II (LNDFH II) is a typical fucosylated human milk oligosaccharide and can be enzymatically produced from lacto-N-tetraose (LNT) by a specific α1,3/4-fucosyltransferase from Helicobacter pylori DMS 6709, referred to as FucT14. Previously, we constructed an engineered Escherichia coli BL21(DE3) with a single plasmid for highly efficient biosynthesis of LNT. In this study, two additional plasmids harboring the de novo GDP-L-fucose pathway module and FucT14, respectively, were further introduced to construct the strain for successful biosynthesis of LNDFH II. FucT14 was actively expressed, and the engineered strain produced LNDFH II as the major product, lacto-N-fucopentaose (LNFP) V as the minor product, and a trace amount of LNFP II and 3-fucosyllactose as very minor products. Additional expression of the α1,3-fucosyltransferase FutM1 from a Bacteroidaceae bacterium from the gut metagenome could obviously enhance the LNDFH II biosynthesis. After optimization of induction conditions, the maximum titer reached 3.011 g/L by shake-flask cultivation. During the fed-batch cultivation, LNDFH II was highly efficiently produced with the highest titer of 18.062 g/L and the productivity yield of 0.301 g/L·h.