Rational Design of an α-1,3-Fucosyltransferase for the Biosynthesis of 3-Fucosyllactose in Bacillus subtilis ATCC 6051a via De Novo GDP-l-Fucose Pathway

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.

Multidimensional Engineering of Escherichia coli MG1655 for the Efficient Biosynthesis of Difucosyllactose

Difucosyllactose (DFL), a representative bisfucosylated oligosaccharide found in human milk, has garnered significant attention due to its immense health benefits. To date, several plasmid-based engineered strains have been established for DFL synthesis. However, these strains face challenges such as antibiotic dependence and plasmid instability, which limit their commercial application in the food industry. For this, plasmid-free Escherichia coli MG1655 strains were established by integrating multicopy numbers of SAMT and fut3Bc into the genome and overexpressing key genes involved in the GDP-l-fucose pathway. To enhance the catalytic efficiency, Fut3Bc was mutated based on AlphaFold 3, obtaining a beneficial mutant Fut3Bc (F24Y). The optimized plasmid-free strain, MGA2S-5, containing 2 copies of SAMT and 4 copies of fut3Bc (F24Y) in the genome was obtained. Eventually, strain MGA2S-5 synthesized 35.04 g/L DFL in a 7 L bioreactor by fed-batch cultivation, with no intermediate products remaining in the medium.

Multistrategy Optimization for High-Yield 3-Fucosyllactose Production in Escherichia coli BL21 Star (DE3)

3-Fucosyllactose (3-FL), an essential component of human milk oligosaccharides, is crucial for infant health. However, the extraction of 3-FL from milk presents a significant challenge. In this study, E. coli BL21 Star (DE3) was engineered for 3-FL biosynthesis, and the gene combinations and metabolic pathways were optimized to obtain a high-yield 3-FL production strain. First, the 3-FL production module was integrated into E. coli. Second, an efficient alpha-1,3-fucosyltransferase was screened. Then, different integration sites were used to optimize the precursor synthesis gene cluster and the transferase genes and to screen for transporter proteins and glycerol utilization genes that could enhance 3-FL production. The 3FL05-1 strain yielded a 3-FL titer of 11.26 g/L in shake flasks. Further amplification in a 5 L bioreactor resulted in a 3-FL titer of 60.24 g/L, which represents the highest reported titer to date.

Efficient fermentative production of lactodifucotetraose by controlling sequential glycosyltransferase reactions in Escherichia coli

Lactodifucotetraose (LDFT) is a human milk oligosaccharide (HMO) that might reduce inflammation in infants. In this study, we established a useful production process of LDFT by engineering two key enzymes, α1,2-fucosyltransferase (α1,2-FucT) and α1,3-fucosyltransferase (α1,3-FucT). First, we verified which of 2'-fucosyllactose (2'-FL) or 3-fucosyllactose (3-FL) (mostly unverified) was more useful. We searched for FucTs that functioned efficiently in vivo against the raw material lactose or the two intermediates 2'-FL or 3-FL by external substrate addition to culture medium. We found that α1,2- FucT (HMFT) from Helicobacter mustelae and the N-terminal truncated form of α1,3-FucT from Bacteroides fragilis (BfFucTΔN10) had high potential. 3-FL was not efficiently converted to LDFT, which might be attributed to the low reactivity of HMFT to 3-FL as well as the low uptake efficiency of 3-FL by LacY, as revealed by a growth test with exogenously added FL as the sole carbon source and heterologously expressed intracellular fucosidase. Furthermore, because 3-FL accumulation had a negative impact on cell growth, we avoided the route passing through 3-FL. By adjusting the copy numbers of HMFT and BffucTΔN10, we produced LDFT from lactose predominantly via 2'-FL. Finally, 17.5 g/L of LDFT (with 6.8 g/L 2'-FL and no 3-FL or residual lactose) accumulated in a 3-L fed-batch culture after 77 h. This study reports the detailed analysis of multiple pathways and shows the control of glycosyltransferases can improve the production efficiency of complex HMOs.

An overview of engineering microbial production of nicotinamide mononucleotide

As the human body gradually ages, the cellular level of NAD+ will decline, which has been found to be related to a variety of age-related diseases. As a precursor of NAD+, NMN is able to effectively promote the synthesis of NAD+ with no significant side effects. Microbial production of NMN holds the potential to lower the production cost and facilitate its wide application. In this review, based on the metabolic pathway of NAD+, we summarize recent advances of metabolic engineering strategies for NMN biosynthesis. An outlook for future optimization to improve NMN production is also discussed.

Recent advances of 3-fucosyllactose in health effects and production

Human milk oligosaccharides (HMOs) have been recognized as gold standard for infant development. 3-Fucosyllactose (3-FL), being one of the Generally Recognized as Safe HMOs, represents a core trisaccharide within the realm of HMOs; however, it has received comparatively less attention in contrast to extensively studied 2'-fucosyllactose. The objective of this review is to comprehensively summarize the health effects of 3-FL, including its impact on gut microbiota proliferation, antimicrobial effects, immune regulation, antiviral protection, and brain maturation. Additionally, the discussion also covers the commercial application and regulatory approval status of 3-FL. Lastly, an organized presentation of large-scale production methods for 3-FL aims to provide a comprehensive guide that highlights current strategies and challenges in optimization.

Combinatorial Optimization Strategies for 3-Fucosyllactose Hyperproduction in Escherichia coli

3-Fucosyllactose (3-FL), an important fucosylated human milk oligosaccharide in breast milk, offers numerous health benefits to infants. Previously, we metabolically engineered Escherichia coli BL21(DE3) for the in vivo biosynthesis of 3-FL. In this study, we initially optimized culture conditions to double 3-FL production. Competing pathway genes involved in in vivo guanosine 5'-diphosphate-fucose biosynthesis were subsequently inactivated to redirect fluxes toward 3-FL biosynthesis. Next, three promising transporters were evaluated using plasmid-based or chromosomally integrated expression to maximize extracellular 3-FL production. Additionally, through analysis of α1,3-fucosyltransferase (FutM2) structure, we identified Q126 residues as a highly mutable residue in the active site. After site-saturation mutation, the best-performing mutant, FutM2-Q126A, was obtained. Structural analysis and molecular dynamics simulations revealed that small residue replacement positively influenced helical structure generation. Finally, the best strain BD3-A produced 6.91 and 52.1 g/L of 3-FL in a shake-flask and fed-batch cultivations, respectively, highlighting its potential for large-scale industrial applications.

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.