Gene Cloning of Streptomyces Phospholipase D P821 Suitable for Synthesis of Phosphatidylserine

A strain, P821, with phospholipase D activity was isolated from soil and identified as a Streptomyces species. The phospholipase D enzyme was purified from a culture broth of the isolated strain using ammonium sulfate precipitation and DEAE-Sepharose, phenyl-Sepharose, and Superose 12 HR column chromatographies. The purified enzyme exhibited an optimum temperature and pH of $55^{\circ}C$ and 6.0, respectively, in the hydrolysis of phosphatidylcholine and remained stable up to $60^{\circ}C$ within a pH range of 3.5-8.0. The enzyme also catalyzed a transphosphatidylation reaction to produce phosphatidylserine with phosphatidylcholine and serine substrates. The optimum conditions for the transphosphatidylation were $30^{\circ}C$ and pH 5.0, indicating quite different optimum conditions for the hydrolysis and transphosphatidylation reactions. The gene encoding the enzyme was cloned by Southern hybridization and colony hybridization using a DNA probe designed from the conserved regions of other known phospholipase D enzymes. The resulting amino acid sequence was most similar to that of the PLD enzyme from Streptomyces halstedii (89.5%). Therefore, the enzyme was confirmed to be a phospholipase D with potential use in the production of phosphatidylserine.