Quantitative Assessment of the Chloroplast Lipidome

International audienceIn plants and algae, photosynthetic membranes have a unique lipid composition. They differ from all other cellular membranes by their very low amount of phospholipids, besides some phosphatidylglycerol (PG), and high proportion of glycolipids. These glycolipids are the uncharged galactolipids, i.e., monogalactosyldiacylglycerol and digalactosyldiacylglycerol (MGDG and DGDG), and an anionic sulfolipid, i.e., sulfoquinovosyldiacylglycerol (SQDG). In all photosynthetic membranes analyzed to date, from cyanobacteria to algae, protists, and plants, the lipid quartet constituted by MGDG, DGDG, SQDG, and PG has been highly conserved but the composition in fatty acids of these lipids can vary a lot from an organism to another. To better understand chloroplast biogenesis, it is therefore essential to know their lipid content. Establishing chloroplast lipidome requires first to purify chloroplast from plant or algae tissue. Here we describe the methods to extract lipids, quantify the lipids of the chloroplast, and qualify and quantify the different lipid classes that might be present in these fractions

Discovery of compounds blocking the proliferation of Toxoplasma gondii and Plasmodium falciparum in a chemical space based on piperidinyl-benzimidazolidinone analogs.

International audience: A piperidinyl-benzimidazolidinone scaffold has been found in the structure of different inhibitors of membrane glycerolipid metabolism, acting on enzymes manipulating diacylglycerol or phosphatidic acid. Screening a focus library of piperidinyl-benzimidazolidinone analogs might therefore identify compounds acting against infectious parasites. We first evaluated the in vitro effects of (S)-2-(dibenzylamino)-3-phenylpropyl 4-(1,2-dihydro-2-oxobenzo[d]imidazol-3-yl)piperidine-1-carboxylate (compound 1) on Toxoplasma gondii and Plasmodium falciparum. In T. gondii, motility and apical complex integrity appeared unaffected, whereas cell division was inhibited at concentrations of compound 1 in the micromolar range. In P. falciparum, proliferation of erythrocytic stages was inhibited, without any delayed death phenotype. We then explored a library of 250 analogs in two steps. We selected 114 compounds with an IC50 cutoff of 2 μM on at least one species and determined in vitro selectivity indexes (SI), based on toxicity against K-562 human cells. We identified compounds with high gains in IC50 (in the 100 nM range) and SI (up to 1,000-2,000). Isobole analyses of two of the most active compounds against P. falciparum indicated that their interaction with artemisin was additive. We propose structure activity relationship (SAR) models, which will be useful for the design of probes to identify the compounds' target(s), and optimizations for mono- or combined-therapeutic strategies