Phospholipase D engineering for improving the biocatalytic synthesis of phosphatidylserine.

Phosphatidylserine is widely used in food, health, chemical and pharmaceutical industries. The phospholipase D-mediated green synthesis of phosphatidylserine has attracted substantial attention in recent years. In this study, the phospholipase D was heterologously expressed in Bacillus subtilis, Pichia pastoris, and Corynebacterium glutamicum, respectively. The highest activity of phospholipase D was observed in C. glutamicum, which was 0.25 U/mL higher than these in B. subtilis (0.14 U/mL) and P. pastoris (0.22 U/mL). System engineering of three potential factors, including (1) signal peptides, (2) ribosome binding site, and (3) promoters, was attempted to improve the expression level of phospholipase D in C. glutamicum. The maximum phospholipase D activity reached 1.9 U/mL, which was 7.6-fold higher than that of the initial level. The enzyme displayed favorable transphosphatidylation activity and it could efficiently catalyze the substrates L-serine and soybean lecithin for synthesis of phosphatidylserine after optimizing the conversion reactions in detail. Under the optimum conditions (trichloromethane/enzyme solution 4:2, 8 mg/mL soybean lecithin, 40 mg/mL L-serine, and 15 mM CaCl2, with shaking under 40 °C for 10 h), the reaction process showed 48.6% of conversion rate and 1.94 g/L of accumulated phosphatidylserine concentration. The results highlight the use of heterologous expression, system engineering, and process optimization strategies to adapt a promising phospholipase D for efficient phosphatidylserine production in synthetic application.