Microbial phospholipase D: Identification, modification and application

Phospholipids (PLs) are major components of biological membranes in all living organisms and have been widely applied in the food, pharmaceutical and cosmetic industries for their numerous nutritional and bioactive functions. Traditionally, PLs have been extracted from egg yolk and soybean using organic solvents; however, the high cost of purification poses a limitation for their further application. Recently, growing attention has been paid to the biological production of PS using phospholipase D (PLD, EC 3.1.4.4). PLD, belonging to PLD superfamily, can catalyze both the hydrolysis of phosphatidylcholine (PC) to phosphatidic acid (PA) and the transphosphatidylation of PC to PL when an appropriate acceptor alcohol is provided. Transphosphatidylation plays a critical role in preparation of functional PLs. To date, approximate 9 genera of microorganisms have been identified and used to prepare PLD. The overall crystal structure PLD and a two-step reaction mechanism have been proposed. In addition, examples of successful modification of PLD such as altering substrate specificity, enhancing thermostability and improving activity have been discussed. In the future, research aimed at searching for novel PLDs with a higher transphosphatidylation activity, determining the crystal structure of more PLDs, and improving the catalytic performance of PLDs through a rational design for the production of PLs should be conducted. Last but not least, more novel and biodegradable solvents for the production of PLD are essential for their further application in daily use.