Expression, Purification, and Characterization of Phosphatidylserine Synthase from Escherichia coli K12 in Bacillus subtilis

Although phosphatidylserine synthase (PSS) from Escherichia coli is an ideal enzyme for phospholipid production, its application in the food industry has been limited because of the low PSS yield. In this study, the pss gene was cloned from E. coli K12 and expressed in Bacillus subtilis DB104, and the recombinant PSS was characterized subsequently. PSS was purified to 39.59-fold, and the highest activity was detected as 13.62 U/mg. The enzyme was found to be stable in a pH range of 6.5−9.5, with optimal pH values of 8.0 for hydrolysis and 7.0 for transphosphatidylation, respectively. The optimal temperature for PSS activity was 35 °C. The enzyme activity could be detected after 1 h of heating at 65 °C. Among the detected detergents and metal ions, Triton X-100, Ca2+, Mn2+, and Co2+ could improve PSS activity. The transformation of phosphatidylcholine to phosphatidylserine under PSS catalyzation was carried out in a biphasic system, which confirmed the actual catalyzing ability of the recombinant protein.