3-fucosyllactose (3-FL) and 2'-fucosyllactose (2'-FL), are two important fucosylated oligosaccharides in human milk. Extensive studies on 2'-FL enabled its official approval for use in infant formula. However, development of 3-FL has been somewhat sluggish due to its low content in human milk and poor yield in enlarged production. Here, an α-1,3-fucosyltransferase mutant was introduced into an engineered Escherichia coli (E. coli) capable of producing GDP-L-fucose, leading to a promising 3-FL titer in a 5.0-L bioreactor. To increase the availability of cofactors (NADPH and GTP) for optimized 3-FL production, zwf, pntAB, and gsk genes were successively overexpressed, finally resulting in a higher 3-FL level with a titer of 35.72 g/L and a yield of 0.82 mol 3-FL/mol lactose. Unexpectedly, the deletion of pfkA gene led to a much lower performance of 3-FL production than the control strain. Still, our strategy achieved the highest 3-FL level in E. coli to date.

Among the human milk oligosaccharides (HMOs), one of the most abundant oligosaccharides and has great benefits for human health is 3′-sialyllactose (3′-SL). Given its important physiological functions and the lack of cost-effective production processes, we constructed an in vitro multi-enzymatic cofactor recycling system for the biosynthesis of 3′-SL from a low-cost substrate. First, we constructed the biosynthetic pathway and increased the solubility of cytidine monophosphate kinase (CMK) with chaperones. We subsequently identified that β-galactosidase (lacZ) affects the yield of 3′-SL, and hence with the lacZ gene knocked out, a 3.3-fold increase in the production of 3′-SL was observed. Further, temperature, pH, polyphosphate concentration, and concentration of divalent metal ions for 3′-SL production were optimized. Finally, an efficient biotransformation system was established under the optimized conditions. The maximum production of 3′-SL reached 38.7 mM, and a molar yield of 97.1% from N-acetylneuraminic acid (NeuAc, sialic acid, SA) was obtained. The results demonstrate that the multi-enzymatic cascade biosynthetic pathway with cofactor regeneration holds promise as an industrial strategy for producing 3′-SL.

Sialyllactose (SL) is one of the most important acidic oligosaccharides in human milk, which plays an important role in the health of infants. In this work, an efficient multi-enzyme cascade was developed in a single whole cell to produce 3′-SL. We constructed two compatible plasmids with double cloning sites to co-express four genes. Different combinations were assessed to verify the optimal catalytic ability. Then, the conversion temperature, pH, and stability under the optimal temperature and pH were investigated. Moreover, the optimal conversion conditions and surfactant concentration were determined. By using the optimal conditions (35 °C, pH 7.0, 20 mM polyphosphate, 10 mM cytidine monophosphate (CMP), 20 mM MgCl₂), 25 mL and 4 L conversion systems were carried out to produce 3′-SL. Similar results were obtained between different volume conversion reactions, which led the maximum production of 3′-SL to reach 53 mM from 54.2 mM of sialic acid (SA) in the 25 mL system and 52.8 mM of 3′-SL from 53.8 mM of SA in the 4 L system. These encouraging results demonstrate that the developed single whole-cell multi-enzyme system exhibits great potential and economic competitiveness for the manufacture of 3′-SL.

Fibrillar type III collagen, characterized by a distinct triple helix structure, is a critical structural component of the mammalian extracellular matrix (ECM). Its unique mechanical properties and biological functions make it a highly valuable biomaterial for medical applications. However, the limited availability of natural human type III collagen (hCOL3) and the defects of animal-derived sources necessitate sustainable alternatives. Here, we developed an integrated molecular engineering strategy for the efficient production of full-length recombinant human type III collagen (rhCOL3) in Komagataella phaffii . The N- and C-terminal propeptides of the rhCOL3α1 chain were rationally redesigned to preserve its intrinsic capability for triple helix formation. Synergistic co-expression of human P4Hαβ and Bacillus anthracis -derived BaP4H achieved a proline hydroxylation level of 52.88%, enabling the stable assembly of rhCOL3 procollagen homotrimers (> 300 kDa). Subsequent optimization, including high-copy-number strain screening, signal sequence substitution (with Ost1 identified as optimal), and co-expression of the molecular chaperones (e.g., BCY1 and ERO1), significantly enhanced productivity. The engineered strain achieved a rhCOL3 procollagen yield of 430 mg/L in a 5-L fed-batch bioreactor. The purified rhCOL3 exhibited a stable triple helix conformation, a melting temperature of 38.87 °C, and the ability to self-assemble into fibrils with a characteristic D-banding pattern. Biological assays confirmed that the rhCOL3 promotes cell proliferation, adhesion, and migration at levels comparable to those of natural collagen. This study establishes a promising platform for the industrial-scale production of bioactive, triple-helical human collagen. Key points: • Synergistic P4Hαβ and BaP4H co-expression achieves 52.88% Hyp level and Tm 38.87 °C. • Ost1 and Bcy1 co-expression elevated rhCOL3 yield to 430 mg/L in a 5-L bioreactor. • Purified rhCOL3 self-assembles into D-banded fibrils resembling native collagen.