Phosphatidylcholine absence affects the secretion of lipodepsipeptide phytoxins in Pseudomonas syringae pv. syringae van Hall CFCC 1336

The effect of methylated phosphatidylethanolamine derivatives on the ionization properties of signaling phosphatidic acid

Phosphatidylethanolamine (PE) and Phosphatidylcholine (PC) are the most abundant glycerophospholipids in eukaryotic membranes. The differences in the physicochemical properties of their headgroups have contrasting modulatory effects on their interaction with intracellular macromolecules. As such, their overall impact on membrane structure and function differs significantly. Enzymatic methylation of PE's amine headgroup produces two methylated derivatives namely monomethyl PE (MMPE) and dimethyl PE (DMPE) which have physicochemical properties that generally range between that of PE and PC. Additionally, their influence on membrane properties differs from both PE and PC. Although variations in headgroup methylation have been reported to affect signaling pathways, the direct influence that these differences exert on the ionization properties of signaling phospholipids have not been investigated. Here, we briefly review membrane function and structure that are mediated by the differences in headgroup methylation between PE, MMPE, DMPE and PC. In addition, using ³¹P MAS NMR, we investigate the effect of these four phospholipids on the ionization properties of the ubiquitous signaling anionic lipid phosphatidic acid (PA). Our results show that PA's ionization properties are differentially affected by changes in phospholipid headgroup methylation. This could have important implications for PA-protein binding and hence physiological functions in cells where signaling events lead to changes in abundance of methylated PE derivatives in the membrane.

Promiscuous phospholipid biosynthesis enzymes in the plant pathogen Pseudomonas syringae

Bacterial membranes are primarily composed of phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL). In the canonical PE biosynthesis pathway, phosphatidylserine (PS) is decarboxylated by the Psd enzyme. CL formation typically depends on CL synthases (Cls) using two PG molecules as substrates. Only few bacteria produce phosphatidylcholine (PC), the hallmark of eukaryotic membranes. Most of these bacteria use phospholipid N-methyltransferases to successively methylate PE to PC and/or a PC synthase (Pcs) to catalyze the condensation of choline and CDP-diacylglycerol (CDP-DAG) to PC. In this study, we show that membranes of Pseudomonas species able to interact with eukaryotes contain PE, PG, CL and PC. More specifically, we report on PC formation and a poorly characterized CL biosynthetic pathway in the plant pathogen P. syringae pv. tomato. It encodes a Pcs enzyme responsible for choline-dependent PC biosynthesis. CL formation is catalyzed by a promiscuous phospholipase D (PLD)-type enzyme (PSPTO_0095) that we characterized in vivo and in vitro. Like typical bacterial CL biosynthesis enzymes, it uses PE and PG for CL production. This enzyme is also able to convert PE and glycerol to PG, which is then combined with another PE molecule to synthesize CL. In addition, the enzyme is capable of converting ethanolamine or methylated derivatives into the corresponding phospholipids such as PE both in P. syringae and in E. coli. It can also hydrolyze CDP-DAG to yield phosphatidic acid (PA). Our study adds an example of a promiscuous Cls enzyme able to synthesize a suite of products according to the available substrates.