Spatial organization of pathway enzymes via self-assembly to improve 2′-fucosyllactose biosynthesis in engineered Escherichia coli

As one of the most abundant components in human milk oligosaccharides, 2′-fucosyllactose (2′-FL) possesses versatile beneficial health effects. Although most studies focused on overexpressing or fine-tuning the expression of pathway enzymes and achieved a striking increase of 2′-FL production, directly facilitating the metabolic flux toward the key intermediate GDP-l -fucose seems to be ignored. Here, multienzyme complexes consisting of sequential pathway enzymes were constructed by using specific peptide interaction motifs in recombinant Escherichia coli to achieve a higher titer of 2′-FL. Specifically, we first fine-tuned the expression level of pathway enzymes and balanced the metabolic flux toward 2′-FL synthesis. Then, two key enzymes (GDP-mannose 4,6-dehydratase and GDP- l -fucose synthase) were self-assembled into enzyme complexes in vivo via a short peptide interaction pair RIAD–RIDD (RI anchoring disruptor–RI dimer D/D domains), resulting in noticeable improvement of 2′-FL production. Next, to further strengthen the metabolic flux toward 2′-FL, three pathway enzymes were further aggregated into multienzyme assemblies by using another orthogonal protein interaction motif (Spycatcher–SpyTag or PDZ–PDZlig). Intracellular multienzyme assemblies remarkably enlarged the flux toward 2′-FL biosynthesis and showed a 2.1-fold increase of 2′-FL production compared with a strain expressing free-floating and unassembled enzymes. The optimally engineered strain EZJ23 accumulated 4.8 g/L 2′-FL in shake flask fermentation and was capable of producing 25.1 g/L 2′-FL by fed-batch cultivation. This work provides novel approaches for further improvement and large-scale production of 2′-FL and demonstrates the effectiveness of spatial assembly of pathway enzymes to improve the production of valuable products in the engineered host strain.