| Summary: | To achieve efficient bio-production of phospholipase D (PLD), PLDs from different organisms were expressed in <i>E.</i><i>coli</i>. An efficient secretory expression system was thereby developed for PLD. First, PLDs from <i>Streptomyces</i> PMF and <i>Streptomyces racemochromogenes</i> were separately over-expressed in <i>E.</i><i>coli</i> to compare their transphosphatidylation activity based on the synthesis of phosphatidylserine (PS), and PLD<sub>PMF</sub> was determined to have higher activity. To further improve PLD<sub>PMF</sub> synthesis, a secretory expression system suitable for PLD<sub>PMF</sub> was constructed and optimized with different signal peptides. The highest secretory efficiency was observed when the PLD * (PLD<sub>PMF</sub> with the native signal peptide Nat removed) was expressed fused with the fusion signal peptide PelB-Nat in <i>E. coli</i>. The fermentation conditions were also investigated to increase the production of recombinant PLD and 10.5 U/mL PLD was ultimately obtained under the optimized conditions. For the application of recombinant PLD to PS synthesis, the PLD properties were characterized and 30.2 g/L of PS was produced after 24 h of bioconversion when 50 g/L phosphatidylcholine (PC) was added.
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