Difucosyllactose (DFL), a fucosylated human milk oligosaccharide, exhibits significant application potential in the food and pharmaceutical industries. However, the microbial production of DFL faces challenges such as the accumulation of the intermediate 2'-fucosyllactose (2'-FL) and the high costs associated with the use of antibiotics and inducers. In this study, we constructed a plasmid- and inducer-free Escherichia coli MG1655 strain to enhance the biosynthesis of DFL while minimizing 2'-FL accumulation. Initially, the de novo DFL biosynthetic pathway was established by introducing different α-1,3-fucosyltransferases (α-1,3-FucT) into a 2'-FL-producing strain. Combinatorial metabolic engineering strategies were then employed to improve DFL accumulation. Subsequently, guided by the in silico multienzyme assembling by reshaping space (iMARS) framework, a fusion enzyme, FucTaY218K-L60-FutC, was rationally designed to effectively alleviate 2'-FL accumulation. Furthermore, modulation of the hydrophobic microenvironment in the substrate-binding pocket of FucTaY218K yielded the beneficial mutant FucTaY218K/W31R. Finally, modifications to the lactose operon significantly improved strain growth while concurrently enhancing DFL production. The best-performing strain achieved a DFL titer of 74 g/L in a 5-L bioreactor, corresponding to a productivity of 0.96 g/L/h, representing the highest productivity reported to date. This study establishes a robust and environmentally friendly platform for the industrial-scale production of DFL and provides a strategy for the microbial synthesis of other high-value human milk oligosaccharides.
Zhiqiang Liu, Binglin Li, Jieying Deng et al.· ACS Synthetic Biology· 0 citations
Trehalose is a nonreducing disaccharide widely used for its biomolecule-protective properties. However, multienzyme cascade production remains limited by low enzyme expression and suboptimal catalytic performance. To address this, thermostable maltooligosyltrehalose synthase (TreY) and trehalohydrolase (TreZ) from Arthrobacter ramosus were individually expressed intracellularly in Bacillus subtilis, and the crude lysates were combined for trehalose biosynthesis, achieving 281.4 g/L trehalose and a yield of 0.7 g trehalose/g maltodextrin. Integrated computational screening identified MalQ-3 from Cyanobacterium stanieri as a suitable 4-α-glucanotransferase for soluble expression. Subsequent semirational engineering generated MalQ-3-M2 (S54P/V472F), with enhanced activity and stability associated with improved substrate-pocket dynamics, thereby facilitating glucan-chain rearrangement and short-chain reutilization. MalQ-3-M2 was separately expressed in B. subtilis and incorporated into the crude-lysate cascade, increasing the trehalose titer to 338 g/L and the yield to 0.85 g trehalose/g maltodextrin. Overall, this work establishes a scalable B. subtilis platform for efficient trehalose production.
Haidong Huang, Yangyang Li, Jin-Song Song et al.· Journal of Agricultural and...· 0 citations
The sustainable production of biomass-based microbial protein (MP) requires efficient microbial cell factories for accumulating cellular protein with high content, which is beneficial both for improving protein production and downstream cellular protein isolation and purification. To overcome the limited protein content of the Saccharomyces cerevisiae, we designed a systematic multilevel metabolic engineering strategy. Initially, single-gene edits based on predictions using the genome-scale model Yeast 9.0.2 and the OptForce algorithm failed to increase protein content due to precursor supply limitations. Enhancing genes in nitrogen metabolic (GDH1, GDH2, GLN1, GLT1) and central carbon (CIT1, IDH1) pathways were implemented to synergistically enhance ammonium assimilation. Subsequently, overexpression of valyl-tRNA synthetase (VAS1) alleviated the translational bottleneck, increasing cellular protein content to 52.3 g/100 g dry cell weight (DCW). The ribosomal synthesis pathway was further enhanced via ribosomal regulator IFH1 and ribosomal protein gene overexpression, with cellular protein content reaching 57.3 g/100 g DCW. Finally, diploidization and global transcriptional regulator SUT1 integration in strain D3 achieved a protein content of 66.5 g/100 g DCW in shake flask culture. Under controlled 5 L bioreactor conditions, its protein content further increased to a peak of 75.2 g/100 g DCW, representing a 50.3% increase over the parental strain Y1. This study developed a multilevel engineering strategy to enhance yeast protein production by optimizing precursor supply, translation machinery, and diploid construction. Using marker-free editing and endogenous gene regulation, it provides both improved protein content and key targets for breeding high-protein microbial strains.
Yang Liu, Caiyin Jin, Wentao Shen et al.· Bioresource Technology· 1 citation
Oxidosqualene cyclases (OSCs) catalyze the cyclization of 2,3-oxidosqualene into diverse triterpenoids, yet their intrinsically low catalytic efficiency restricts biosynthetic productivity. Here, we establish a mechanism-guided synergistic engineering strategy that extends beyond conventional active-site engineering by integrating distal substrate access regulation with catalytic microenvironment optimization to enhance the catalytic performance of CrAS from Catharanthus roseus. Structural modeling and mechanistic analyses revealed a conserved catalytic framework involving carbocation-mediated polycyclization and identified a surface-exposed constriction region that regulates substrate access. Guided by these insights, distal surface engineering of the constriction region was synergistically combined with active pocket optimization. The resulting combinatorial mutant, M3 (L323A/T327K/N565I), exhibited a 95.2% increase in catalytic efficiency and enhanced α-amyrin and β-amyrin by 53.2% and 49.7%, reaching 158 mg/L and 63 mg/L, respectively. Multi-scale analyses combining molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) calculations revealed that the enhanced catalytic performance is attributable to increased flexibility of the substrate access pathway, reinforced electrostatic and cation-π interactions, and reduced reaction energy barriers. Notably, distal mutation T327K improved substrate ingress through dynamic modulation of the protein surface, while N565I optimized the catalytic microenvironment by enhancing hydrophobic packing and stabilizing key intermediates. Overall, our findings establish a generalizable framework for engineering complex cyclases and provide a foundation for the sustainable microbial production of high-value triterpenoids.
Yangyang Li, K. Jin, Jiangong Lu et al.· Biotechnology and Bioenginee...· 0 citations