Phospholipase D-catalyzed synthesis of new phospholipids with polar head groups

Study on the mechanism of efficient extracellular expression of toxic streptomyces phospholipase D in Brevibacillus choshinensis under Mg2+ stress

Background

Phospholipase D (PLD) has significant advantages in the food and medicine industries due to its unique transphosphatidylation. However, the high heterologous expression of PLD is limited by its cytotoxicity. The present study sought to develop an efficient and extracellular expression system of PLD in the non-pathogenic Brevibacillus choshinensis (B. choshinensis).

Results

The extracellular PLD was effectively expressed by the strong promoter (P2) under Mg2+ stress, with the highest activity of 10 U/mL. The inductively coupled plasma–mass spectrometry (ICP-MS) results elucidated that the over-expression of PLD by P2 promoter without Mg2+ stress induced the ionic homeostasis perturbation caused by the highly enhanced Ca2+ influx, leading to cell injury or death. Under Mg2+ stress, Ca2+ influx was significantly inhibited, and the strengths of P2 promoter and HWP gene expression were weakened. The study results revealed that the mechanism of Mg2+ induced cell growth protection and PLD expression might be related to the lowered strength of PLD expression by P2 promoter repression to meet with the secretion efficiency of B. choshinensis, and the redistribution of intracellular ions accompanied by decreased Ca2+ influx.

Conclusions

The PLD production was highly improved under Mg2+ stress. By ICP-MS and qPCR analysis combined with other results, the mechanism of the efficient extracellular PLD expression under Mg2+ stress was demonstrated. The relatively low-speed PLD expression during cell growth alleviated cell growth inhibition and profoundly improved PLD production. These results provided a potential approach for the large-scale production of extracellular PLD and novel insights into PLD function.

Polar Head Modified Phospholipids by Phospholipase D-Catalyzed Transformations of Natural Phosphatidylcholine for Targeted Applications: An Overview

This review describes the use of phospholipase D (PLD) to perform the transphosphatidylation of the most common natural phospholipid (PL), phosphatidylcholine (PC) to obtain polar head modified phospholipids with real targeted applications. The introduction of different polar heads with distinctive physical and chemical properties such as charge, polarity and dimensions allows the obtainment of very different PLs, which can be exploited in very diverse fields of application. Moreover, the inclusions of a bioactive moiety in the PL polar head constitutes a powerful tool for the stabilization and administration of active ingredients. The use of this biocatalytic approach allows the preparation of compounds which cannot be easily obtained by classical chemical methods, by using mild and green reaction conditions. PLD is a very versatile enzyme, able to catalyze both the hydrolysis of PC to choline and phosphatidic acid (PA), and the transphosphatidylation reaction in the presence of an appropriate alcohol. The yield of production of the desired product and the ratio with the collateral PA formation is highly dependent on parameters such as the nature and concentration of the alcohol and the enzymatic source. The application of PLD catalyzed transformations for the production of a great number of PLs with important uses in medical, nutraceutical and cosmetic sectors will be discussed in this work.

Differences in the effect of phosphatidylinositol 4,5-bisphosphate on the hydrolytic and transphosphatidylation activities of membrane-bound phospholipase D from poppy seedlings

The hydrolytic activity of phospholipase D (PLD) yielding phosphatidic acid from phosphatidylcholine and other glycerophospholipids is known to be involved in many cellular processes. In contrast, it is not clear whether the competitive transphosphatidylation activity of PLD catalyzing the head group exchange of phospholipids has a natural function. In poppy seedlings (Papaver somniferum L.) where lipid metabolism and alkaloid synthesis are closely linked, five isoenzymes with different substrate and hydrolysis/transphosphatidylation selectivities have been detected hitherto. A membrane-bound PLD, found in microsomal fractions of poppy seedlings, is active at micromolar concentrations of Ca(2+) ions and needs phosphatidylinositol 4,5-bisphosphate (PIP2) as effector in the hydrolysis of phosphatidylcholine (PC). The optimum PIP2 concentration at 1.2 mol% of the concentration of the substrate PC indicates a specific activation effect. Transphosphatidylation with glycerol, ethanolamine, l-serine, or myo-inositol as acceptor alcohols is also activated by PIP2, however, with an optimum concentration at 0.6-0.9 mol%. In contrast to hydrolysis, a basic transphosphatidylation activity occurs even in the absence of PIP2, suggesting a different fine-tuning of the two competing reactions.

Substrate specificity in phospholipid transformations by plant phospholipase D isoenzymes

Phospholipase D (PLD) catalyzes the hydrolysis and transesterification of glycerophospholipids at the terminal phosphodiester bond. In many plants, several isoforms of PLD have been identified without knowing their functional differences. In this paper, the specificities of two PLD isoenzymes from white cabbage (Brassica oleracea var. capitata) and two ones from opium poppy (Papaver somniferum L.), which were recombinantly produced in Escherichia coli, were compared in the hydrolysis of phospholipids with different head groups and in the transphosphatidylation of phosphatiylcholine with several acceptor alcohols. In a biphasic reaction system, consisting of buffer and diethyl ether, the highly homologous isoenzymes are able to hydrolyze phosphatidylcholine, -glycerol, -ethanolamine, -inositol and - with one exception - also phosphatidylserine but with different individual reaction rates. In transphosphatidylation of phosphatidylcholine, they show significant differences in the rates of head group exchange but with the same trend in the preference of acceptor alcohols (ethanolamine>glycerol>>l-serine). For l- and d-serine a stereoselectivity of PLD was observed. The results suggest a physiological relevance of the different hydrolytic and transphosphatidylation activities in plant PLD isoenzymes.

Dose response effects of dermally applied diethanolamine on neurogenesis in fetal mouse hippocampus and potential exposure of humans

Diethanolamine (DEA) is a common ingredient of personal care products. Dermal administration of DEA diminishes hepatic stores of the essential nutrient choline and alters brain development. We previously reported that 80 mg/kg/day of DEA during pregnancy in mice reduced neurogenesis and increased apoptosis in the fetal hippocampus. This study was designed to establish the dose-response relationships for this effect of DEA. Timed-pregnant C57BL/6 mouse dams were dosed dermally from gestation day 7-17 with DEA at 0 (controls), 5, 40, 60, and 80 mg/kg body/day. Fetuses (embryonic day 17 [E17]) from dams treated dermally with 80 mg/kg body/day DEA had decreased neural progenitor cell mitosis at the ventricular surface of the ventricular zone (hippocampus, 54.1 +/- 5.5%; cortex, 58.9 +/- 6.8%; compared to controls; p < 0.01). Also, this dose of DEA to dams increased rates of apoptosis in E17 fetal hippocampus (to 177.2 +/- 21.5% of control; measured using activated caspase-3; p < 0.01). This dose of DEA resulted in accumulation of DEA and its metabolites in liver and in plasma. At doses of DEA less than 80 mg/kg body/day to dams, there were no differences between treated and control groups. In a small group of human subjects, dermal treatment for 1 month with a commercially available skin lotion containing 1.8 mg DEA per gram resulted in detectable plasma concentrations of DEA and dimethyldiethanolamine, but these were far below those concentrations associated with perturbed brain development in the mouse.