The substrate requirements of phospholipase D

Reactive Deep Eutectic Solvents (RDESs): A New Tool for Phospholipase D-Catalyzed Preparation of Phospholipids

The use of Reactive Deep Eutectic Solvents (RDESs) in the preparation of polar head modified phospholipids (PLs) with phospholipase D (PLD)-catalyzed biotransformations has been investigated. Natural phosphatidylcholine (PC) has been submitted to PLD-catalyzed transphosphatidylations using a new reaction medium composed by a mixture of RDES/buffer. Instead of exploiting deep eutectic solvents conventionally, just as the reaction media, these solvents have been designed here in order to contribute actively to the synthetic processes by participating as reagents. RDESs were prepared using choline chloride or trimethyl glycine as hydrogen-bond acceptors and glycerol or ethylene glycol, as hydrogen-bond donors as well as nucleophiles for choline substitution. Specifically designed RDES/buffer reaction media allowed the obtainment of PLs with optimized yields in the perspective of a sustainable process implementation.

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.

Valorization of Corn Seed Oil Acid Degumming Waste for Phospholipids Preparation by Phospholipase D-Mediated Processes

This work focused on the phospholipase D-mediated treatment of the waste residue coming from acid degumming, which constitutes the second part of the degumming step in the crude corn edible oil refining process. This industrial process produces a complex by-product (called gum), a mixture containing phospholipids (PLs) whose composition depends on the nature of the oil source. This residue is usually disposed of with the consequential costs and environmental concerns. An efficient multistep protocol of physical separations of the PL-rich fraction from waste gums has been set up, including centrifugation, precipitation and solvent partitioning. This waste stream, which is thoroughly characterized after the concentration process, constitutes a renewable feedstock for the production of value-added PLs with modified polar head-exploiting phospholipase D-mediated biotransformations, which have been successfully performed on this complex natural mixture. The valorization of these waste gums through the production of high value PLs for targeted applications paves the way to a new alternative approach for their disposal, which could be of great interest from a circular economy perspective.

Visualizing complexes of phospholipids with Streptomyces phospholipase D by automated docking

The automated docking program AutoDock was used to dock nine phosphatidic acids (PAs), six phosphatidylcholines, five phosphatidylethanolamines, four phosphatidylglycerols, one phosphatidylinositol and two phosphatidylserines, which have two identical saturated fatty acid residues with an even numbers of carbon atoms, onto the active site of Streptomyces sp. PMF phospholipase D (PLD). Two PAs with one double bond on the fatty acid chain linked to the C2 of the glycerol residue were also docked. In general, binding energies become progressively more negative as fatty acid residues become longer. When these residues are of sufficient length, one is coiled against a hydrophobic cliff in a well that also holds the glycerol and phosphate residues and the head group, while the other generally is bound by a hydrophobic surface outside the well. Phosphatidylcholines have the only head group that is firmly bound by the active site, giving a possible structural explanation for the low selectivity of Streptomyces PLD for other phospholipid substrates.

The reaction mechanism of phospholipase D from Streptomyces sp. strain PMF. Snapshots along the reaction pathway reveal a pentacoordinate reaction intermediate and an unexpected final product

Almost all enzyme-catalysed phosphohydrolytic or phosphoryl transfer reactions proceed through a five-coordinated phosphorus transition state. This is also true for the phospholipase D superfamily of enzymes, where the active site usually is made up of two identical sequence repeats of an HKD motif, positioned around an approximate 2-fold axis, where the histidine and lysine residues are essential for catalysis. An almost complete reaction pathway has been elucidated by a series of experiments where crystals of phospholipase D from Streptomyces sp. strain PMF (PLD(PMF)) were soaked for different times with (i) a soluble poor, short-chained phospholipid substrate and (ii) with a product. The various crystal structures were determined to a resolution of 1.35-1.75 A for the different time-steps. Both substrate and product-structures were determined in order to identify the different reaction states and to examine if the reaction actually terminated on formation of phosphatidic acid (the true product of phospholipase D action) or could proceed even further. The results presented support the theory that the phospholipase D superfamily shares a common reaction mechanism, although different family members have very different substrate preferences and perform different catalytic reactions. Results also show that the reaction proceeds via a phosphohistidine intermediate and provide unambiguous identification of a catalytic water molecule, ideally positioned for apical attack on the phosphorus and consistent with an associative in-line phosphoryl transfer reaction. In one of the experiments an apparent five-coordinate phosphorus transition state is observed.

Synthesis and antiproliferative activity of alkylphosphocholines

Alkylphosphocholines (APC) with one or more methylene groups in the alkyl chain replaced by oxygen atoms or carbonyl groups, or both have been assembled modularly using omega-diols as central building blocks. Out of 25 new compounds of this kind, 11 were evaluated for their antiproliferative activity on four cell lines and compared with miltefosine to evaluate their hemolytic activity (HA) and cytotoxicity on non-tumoral cells (MT2), used as markers of adverse effects. Compound 13 was more active on cancer cell lines than on non-tumoral cells and the data were similar for MTT and thymidine incorporation assays. It had less HA than miltefosine. Compound 13 could therefore be a candidate for the preparation of compounds with higher cytotoxicity on cancer cells and lower general toxicity.